Metabolic adrenergic changes during submaximal exercise and in the recovery period in man J. M. PEQUIGNOT, L. PEYRIN, M. H. MAYET, AND R. FLANDROIS Laboratoire de Physiologic, Centre National de la Recherche Scientifique and Faculte’ de Mkdecine Grange-Blanche, Universite’ Claude Bernard, 69373 Lyon Ce’dex 2, France
PEQUIGNOT, J.M.,L. PEYRIN, M.H. MAYET,AND R. FLANMetabolic adrenergic changes during submaximal exercise and in the recovery period in man. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47(4): 701-705,1979.-The urinary excretion of dihydroxyphenylalanine (DOPA), catecholamines (CA) [ dopamine (DA), norepinephrine (NE), and epinephrine (E)], their 3-0-methylated derivatives [3-O-methyldopamine (3-MT), normetanephrine (NMN), and metanephrine (MN)], and their deaminated metabolites [dihydroxyphenylacetic acid (DOPAC) and vanilmandelic acid (VMA)] was studied in six healthy men, at rest, during short-term (15 min) or exhaustive submaximal exercise, and in the 2-h postexercise recovery period. During short-term exercise only NE and VMA excretions increased, whereas in postexercise period only DA output was enhanced. Exhaustive muscular work induced a rise in NE and E excretion during the test, and an increase in DA, NE, and NMN urinary levels during postexercise recovery, while the output of deaminated metabolites was unaltered. It is concluded that both release and synthesis of CA are stimulated by submaximal exercise, which induces, in addition to NE, a specific release of DA. A possible role of NE in lipid mobilization during recovery from exhaustive muscular work is evoked. The origin and role of released DA are also discussed. DROIS.
urinary catecholamines; postexercise recovery
dopamine;
adrenergic
metabolites;
MATERIALSANDMETHODS
Subjects
that the sympathoadrenal system is stimulated by muscular work, as shown by the enhanced levels of catecholamines (CA) in plasma and urine (6, 9, 12, 13, 23). Little attention has been paid to urinary excretion of CA metabolites during exercise (6, 13). Nevertheless, interesting knowledge about the functional activity of the adrenergic system may be drawn from study of the adrenergic urinary pattern, including CA, their precursors, and their metabolites (27). It is well known that body CA may be classified in two distinct pools, functional and tissue, with different metabolic pathways. It is now accepted that urinary CA and methoxyamines are related to the release activity of the adrenergic system (from the functional pool), whereas deaminated metabolites [dihydroxyphenyl acetic acid (DOPAC) and vanilmandelic acid (VMA)] are rather concerned with sympathetic and chromaffin intratissue events, including synthesis and storage of the CA tissue pool (17). In addition to norepinephrine (NE) and epinephrine (E), dopamine (DA) is normally present in urine and THERE IS EVIDENCE
0161-7567/79/0000-0000$01.‘25
plasma. Although DA is the immediate precursor in the synthesis of NE and E, both its origin and role remain to be discovered. Peripheral dopaminergic neurons have been described in sympathetic ganglia (15). Recently Snider et al. (29) have postulated that some noradrenergic fibers may release DA as neurotransmitter in stress circumstances. Moreover dopaminergic receptors are present in many peripheral tissues (30). Thus, it seems to be of interest to define the pattern of urinary DA excretion during heavy muscular work. The present study has been designed to determine the influence on the adrenergic and dopaminergic metabolism of submaximal exercise preformed either for 15 min or until exhaustion. To this end, we have studied the urinary excretion of the three CA (DA, NE, and E) and dihydroxyphenylalanine (DOPA), and their main metabolites, methyoxyamines [3-0-methyldopamine (3-MT), normetanephrine (NMN), and metanephrine (MN)] and deaminated metabolites, DOPAC and VMA, during the exercise period and in the postexercise recovery.
Copyright
0 1979 the American
Physiological
Six healthy male subjects voluntarily participated in the experiment. Their age, height, weight, and maximal oxygen uptake determined directly by gaseous exchange method averaged (mean t SE) 33 t 4 yr, 175 t 4 cm, 65 t 2kg, and 48.0 t 1.6 ml. kg-’ amin-‘, respectively. Experimental
Procedures
For exercise, the subjects pedaled a Monark cycle ergometer at a work load individually calculated to approximate 80% of their maximal oxygen uptake (VO, max). The trials were conducted around 2 P.M., at least 2 h after a light meal; the test was performed either for 15 min or until exhaustion (45-60 min). Except for exercise time, subjects were at rest in sitting or standing positions, and were advised to avoid strong mental activity; tobacco, coffee, and tea were not allowed. Moreover, to avoid emotional stress before the test, the subjects were progressively adapted by pedaling the bicycle ergometer on four separate occasions in the same conditions as those of the experiment. Urinary samples were collected during two consecutive 2-h periods before the ergometric work and subsequently Society
701
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702
PEQUIGNOT,
in two 2-h periods after the start of the exercise (Fig. 1). Each urine sample was acidified to pH 1 with 5 N HCl and stored at -25OC until analysis. Analytical
Procedures
For all the metabolites studied, analysis was performed on the total (free + conjugated) urinary content, except for VMA, which was studied in the free form. Hydrolysis was effected by boiling urinary samples at pH 1 for 10 min for DA, NE, E, DOPA, and DOPAC, and for 30 min for methoxyamines (3-MT, NMN, and MN). Determination of CA, DOPA, and DOPAC. To determine the CA (DA, NE, and E), DOPA, and DOPAC content in the 2Oml hydrolyzed urine sample the compounds were extracted by a double-step chromatographic procedure, involving purification on aluminum oxide and further separation on an Amberlite CG 50-NHJ+ column (5). In the eluates DA, NE, E, DOPA, and DOPAC were assayed according to the automated procedures developed in our laboratory: DA (1, 5), NE and E (24), DOPA (2), and DOPAC (25). Determination of methoxyamines. Methoxyamines (3MT, NMN, and MN) were extracted from 10 ml hydrolyzed urine by a double-step chromatographic procedure involving purification on Dowex 50 WXZ-H+ column and separation of the three above amines on Amberlite CG 50-NH4+ (3). In the final eluates, 3-MT, NMN, and MN were estimated by automated fluorimetric methods previously developed (1). Determination of VMA. Urinary VMA was extracted by means of ethyl acetate and analyzed by paper chromatography as described in a previous report (25). Determination of creatinine. Creatinine was determined according to the method of Paget et al. (22). Calculations Urinary excretion of CA or metabolites was expressed as ng or pg/mg of creatinine. The excretion rate of creatinine was unaffected by exercise whatever the duration might be (1,168 t 84 pgernin-’ at rest, 1,117 t 175 r_lg min-’ during short-term exercise, and 1,125 t 125 pg. min-’ during exhaustive exercise). Data were analyzed using a t test for paired observations and statistical significance was selected at P < 0.05. l
submaximal exercise
12
1 first urine collection I pre
FIG.
2 P.M.
second I urine collection
I
_ exercise periods
1. Schedule
representing
MAYET,
AND
FLANDROIS
RESULTS
Excretion of all compounds showed no change in the two successive urinary samples studied during the control preexercise periods. Thekefore, the exercise and postexercise data were compared to the mean control value of both preexercise periods. Fifteen-Minute
Exercise
Bouts
During the exercise period the sum of E, NE, and their metabolites (NE + NMN + E + VMA) increased 77% above control levels (ZCA in Table l), while the sum of DA metabolites (ZDA in Table 1) was unchanged. Urinary NE and VMA excretions were enhanced above baseline values by 49 and 83%, respectively (Figs. 2 and 3). No change in the urinary amounts of other metabolites was detectable. During the postexercise period the sums of amines and of methoxyamines @Met) remained elevated (Table 1) but urinary NE and VMA levels returned to base line and the output of E was significantly diminished (Figs. 2 and 3). In contrast, the sum DA + 3-MT was increased 63% (Table 1) and the urinary excretion of DA was enhanced 41% compared to resting levels (Fig. 2). Exhaustive
Exercise
Bouts
During the exercise period exhaustive muscular work resulted in much higher urinary excretion of NE (+ 112%) and E (+ 71%) (Fig. 2). A concomitant rise in the sum of methoxyamines (3 MT + NMN + MN) was noticed (+ 31% above preexercise levels) (ZMet in Table 2). Also the sum of amines (DA + NE + E) (Table 2) and the urinary output of DA (Fig. 2) tended to increase by 70 and 57%, respectively, but not significantly (P < 0.10). Surprisingly the concentration of each acid metabolite (DOPAC and VMA) in urine remained unchanged during prolonged exercise (Fig. 3). The urinary metabolic pattern of CA was strikingly altered during the postexercise period, as shown in Table 2 and Fig. 2 (compare to control). Both the sums of amines and of methoxyamines remained as elevated as during the exercise period (Table 2). Among these compounds, DA, NE, and MN concentrations remained at their exercise levels (Fig. 2), while 3 MT and NMN output was even more enhanced 82 and 45%, respectively, above basal rate (P < 0.10 and P < 0.05, respectively). DISCUSSION
1
10A.M.
PEYRIN,
6 P.M.
1 third urine collection
1 fourth urine collect I
I I exercise period general
I ion
1 postSexercise period
outline
of the study.
I
A constant fraction of CA secretion is found in urine, together with metabolites their excretion is apparent in a short delay after the release. From the results obtained by Goodall and Alton (7) after intravenous infusion of E, it may be assumed that 15-25% of the released amine appears in the urine 1 h after the adrenergic stimulation. On this basis, 2-h urinary collection periods were chosen to study the effects of submaximal exercise. Among urinary metabolites, CA and the corresponding 3-0-methylated derivatives are considered a satisfactory index of sympathoadrenal release activity; furthermore, because about 90% of the E originates from the adrenal
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METABOLIC
ADRENERGIC
1. Metabolic
TABLE
CHANGES
adrenergic
AND
EXERCISE
changes
induced
Control Camines CMet Cacids CCA CDA ZCA/ZDA DA + 3-MT NE + NMN E+MN CMet/Camines
1,198 432 8,200 4,584 5,297 0.902 1,155 310 164 0.398
703 by submaximal Exercise
t 305 t 52 t 1,500 t 889 -+ 961 k 0.182 t 314 t, 27 k 28 sfr 0.048
1,690 543 11,300 8,092 5,475 2.036 1,631 365 216 0.414
t t t t t t t t k t
short-term
exercise
A from Control
556 99 1,600 1,624 1,292 0.640 589 40 61 0.125
492 111 3,100 3,508 178 1.134 476 55 52 0.016
in healthy
Postexercise
t 307 t59 k 1,700 t 1,640* t 1,106 AI 0.701 t 329 t 27 t, 47 k 0.127
1,635 555 8,300 5,903 4,675 1.365 1,657 346 187 0.347
-+ k t t t t t t t t
men
Recovery
A from Control
258 82 900 1,011 495 0.294 295 45 34 0.042
438 123 100 1,319 622 0.463 502 36 23 0.051
t 206* t 38* t 1,300 t 1,211 zk 616 t 0.418 t 194* t 35 & 20 f: 0.059
Values are means t SE of urinary excretion of adrenergic and dopaminergic metabolites in ng/mg creatinine. Camines = DA + NE + E; CMet = 3-MT + NMN + MN; Cacids = DOPAC + VMA; CCA = NE + NMN + E + MN + VMA; CDA = DA + 3-MT + DOPAC. A, deviation from base-line values. See text for meanings of abbreviations. * Significantly different from zero, P c 0.05 (t test for paired observations; n = 6).
al .-‘c 320
.-
4J
; 240
0
PRE - EXERCISE
m
EXERCISE
m
POST-EXERCISE
NMN
c
1T
MN
DA. 10-l
depleted of striatal DA by locally injected 6-hydroxydopamine (6-OHDA) (26). DA has been found in the adrenal medullary secretion of some species (4% of total CA in the adrenal blood of sheep (16)). If this assumption may be extrapolated to man the DA amounts released from this source would be negligible compared to the high urinary excretion of DA in the basal state and, a fortiori, under adrenergic stimulation. DA is also associated with NE in most-sympathetic fibers and has been found at high levels in several tissues (lungs, bronchi, intestine, and carotid bodies) and in the small intensely fluorescent (SIF) cells of sympathetic ganglia (see for review Ref. 27). The relative contribution of these DA peripheral stores to urinary excretion is unknown; however, the SIF cells may represent interesting sources in this respect, since they are located inside the sympathetic ganglion very close to blood capillary vessels and they are able to release DA under preganglionic nerve stimulation (15). On the other hand, according to Snider et al.
)rg / mg creat
FIG. 2. Mean tSE urinary excretions of dihydroxyphenylalanine (DOPA), dopamine (DA), 3-o-methyldopamine (3-MT), norepinephrine (NE), normetanephrine (NMN) , epinephrine (E), and metanephrine (MN) in 6 men. Determinations were made on samples collected I) before exercise bouts (for each experiment, control value resulted from two successive urinary 2-h collections (preexercise periods: cZear bars)), 2) during a 2-h interval including a submaximal exercise (pedaling at a work load corresponding to 80% of maximal aerobic power) (exercise period: crosshatched bars), and 3) during a consecutive 2-h interval (postexercise period: stippled bars). Upper panel: short-term exercise bouts (15 min). Lowerpanel: exhaustive exercise bouts (45-60 min). See Fig. 1 for additional information. Significant differences from preexercise values indicated by *P < 0.05 (t test for paired observations;
n = 6).
medulla and 90% of the NE is furnished by sympathetic nerve endings (31), the estimation of E + MN and NE + NMN urine levels provides convenient parameters to analyze the relative activity of the glandular and neuronal adrenergic compartments (17). The origin of DA and 3-MT is unclear. Although very large amounts of DA are present in central dopaminergic neurons, it is very unlikely that urinary DA in man has a central origin, because we have not been able to demonstrate any change in DA excretion in rats unilaterally
inine
1-1
PRE-EXERCISE
LTq
EXERCISE
m
POST-EXERCISE
vMA short -term exefc ise 10 8
+
exhaustive lxercise
T
DOPAC short-term exercise
exhaustive exercise
6 4 2
FIG. 3. Mean tSE urinary excretions of vanilmandelic acid (VMA) and dihydroxyphenylacetic acid (DOPAC) in 6 men. Determinations were made on samples collected I) before the exercise bouts (for each experiment, the control value resulted from two successive urinary 2-h collections (preexercise periods: cZear bars)), 2) during a 2-h interval including a submaximal short-term, 15 min, or exhaustive, 45-60 min, exercise (pedaling at a work load corresponding to 80% of maximal aerobic power) (exercise period: cross-hatched bars), and 3) during a consecutive 2-h interval (postexercise period: stippled bars). See Fig. 1 for additional information. Significant differences from preexercise values indicated by *P < 0.05 (t test for paired observations; n = 6).
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704
PEQUIGNOT,
TABLE
2. Metabolic
adrenergic
changes induced
Exercise
Control Camines CMet Cacids CCA CDA XA/XDA DA + 3-MT NE + NMN E+MN XMet/Xamines Values Table 1.
1,066 361 10,900 6,185 6,133 1.195 960 274 96 0.536
t t t t t t t, t -+ t,
by submaximal
373 94 1,300 1,280 1,015 0.322 415 63 18 0.189
are means t, SE of urinary excretion * Significantly different from zero,
1,711 474 10,500 5,662 7,117 0.765 1,641 377 167 0.345
t 405 t 114 t, 1,800 t 1,398 -+ 929 t 0.133 k 391 t, 58 t 55 t 0.084
exhaustive A from Control 644 113 380 523 984 0.430 681 103 71 0.191
PEYRIN,
MAYET,
AND
exercise in healthy
men
Postexercise
t 355 t 35* -+ 1,360 t 606 t, 1,034 t, 0.223 t 430 t 38* t38 t 0.226
of adrenergic and dopaminergic metabolites in ng/mg P < 0.05 (t test for paired observations; n = 6).
(29), under severe stress some noradrenergic neurons might become partially dopaminergic, due to the relatively limited capacity of the cell to synthesize NE from DA, and might thus release DA. With regard to deaminated CA metabolites present in urine, there is evidence that they are related to intraneuronal or intrachromaffin metabolism by monoamine oxidase, and may reflect intense synthesis activity overpassing storage capacities (14, 17). VMA is formed both in the adrenal gland and in sympathetic neurons from E and/or NE. DOPAC is an important metabolite of DA (25), but no precise informati0.n about its topographic origin is available. In the present investigation, it appears that exhaustive submaximal exercise (80% VOW max) alters markedly the urinary metabolic pattern of CA, both during and after the test, while smaller changes are induced by short-term submaximal work. In accordance with previous studies (12, 13), we observed during the 15min exercise bouts, an increase in NE excretion (Fig. 2), which certainly originated from sympathetic nerve endings. Under the same conditions, we previously observed a rise in plasma E in addition to NE (23), whereas in the present study urinary excretion of E failed to increase (Fig. 2). As the absolute increase of E is generally smaller than that of NE (23), measurements in a 2-h urine collection may not detect short changes in the plasma concentrations of E. Moreover, the enhanced urinary VMA level (Fig. 3) seems to indicate that the synthesis of CA was stimulated by shortterm submaximal exercise. This is in line with the finding that in rats moderate exercise prolonged for 2.5 h led to an activation of CA synthesis in adrenals and heart (18). The exhaustive exercise has acute effects on the urinary metabolic pattern of NE and E. The increased excretion of these amines (Fig. 2) was not due to changes in the catechol-O-methyltransferase activity because the ratio of methoxyamines to amines remained unchanged (Table 2). Contrary to observations of the 15min test, VMA excretion during the exhaustive exercise period was unaltered (Fig. 3). This unchanged VMA excretion, together with the active release of CA may indicate that, in the exhaustive conditions, the strong stimulation of CA secretion surpasses the capacities of intraneuronal storage of newly synthetized CA. In other words, both release and synthesis processes are stimulated by exercise, but CA are released as soon as they are formed.
1,571 558 11,400 7,632 6,015 1.341 1,562 420 147 0.371
t & I!I t t t k t, t t
FLANDROIS
Recovery
A ‘from Control
415 182 2,400 2,965 566 0.517 439 106 47 0.071
505 197 540 1,447 119 0.145 602 146 51 0.165
creatinine.
Abbreviations
t 87* t 99 -+ 1,800 zk 2,051 t 882 t 0.51 t 109* t 59* t29 t 0.193
as indicated
in
There is evidence to suggest that CA are important the energy substrate mobilization factors in controlling from endogenous stores during exercise. Indeed P-adrenergic blockade by propranolol is able to inhibit totally the exercise-induced lipolysis, partially the glycogenolysis in dogs, (11) and alter the working capacity (20). Furthermore, we have found that, in man, the exerciseinduced release of CA (NE and E) was enhanced by fasting and was significantly correlated to the blood levels of energy substrates (glucose, lactate, and glycerol) (Pequignot, Peyrin, and Peres, unpublished observation). In the-present-study, another striking effect of submaximal exhaustive work was the sustained elevated excretion of NE and its metabolite NMN during the postexercise recovery (Fig. 2, Table 2), demonstrating a prolonged system. Hagenfeldt and activation of the adrenergic Wahren (8) have reported th .at the fre le fatty acid release into plasma is raised during recovery from exercise. Accordingly, it can also be reasonably assumed from the present results that in the period following the prolonged muscular work the increased sympathetic activity would control lipid mobilization. Thus, because the muscle pool of triglycerides is mobilized during the muscular work (lo), NE would possibly contribute to the restoration of the lipidic muscular stores after the exhaustive test. Naftchi et al. (19) noted a concomitant release of DA and NE in quadriplegic subjects during hypertensive stress. In the present study the submaximal exercise was able to induce a large release of DA in the postexercise period in addition to NE in healthy men. This was shown by the rise in urinary excretion of DA (Fig. 2) and by the increased sum DA + 3-MT (Tables 1 and 2). DA is generally considered as a precursor for NE in the peripheral adrenergic system. However, the concomitant increase in DA and NE in this study does not seem to result from exhaustion of NE endogenous stores leading to DA accumulation, as the release of NA remained at a very high level during and after the exhaustive exercise (Fig. 2). Thus, there is evidence that the release of DA is specific; however, its origin cannot be assessed. The role of DA in the working performance and in the postexercise recovery is less clear than that of other CA. DA, like NE, is able to exert metabolic effects on carbohydrate and lipid stores (21). In the cardiovascular field, DA is a less hypertensive agent than NE but exhibits a particular vasodilating action on the splanchnic, renal, and coronary vascular bed (28). On the other hand, in sympathetic
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METABOLIC
ADRENERGIC
CHANGES
AND
705
EXERCISE
ganglia, it has been shown that DA from SIF cells is able neurons and to to depress the activity of sympathetic inhibit NE release (15). In agreement with this knowledge, and with the fact that DA release was especially evident in the recovery period after short-term as well as after exhaustive exercise (Fig. 2)) the role of the increased release of DA o bserved in our study might be to enhance the metabolic effects of other CA or, conversely, to regulate NE release to reduce the neuromediator losses. Alternatively, both types of action might occur simultaneously, but it cannot be decided which of these mechanisms would be predominant. In conclusion, the submaximal exercise was able to induce changes in urinary metabolic pattern of CA, indicating increased synthesis and release of these neuro-
hormones. After exhaustion, the secretion of NE was prolonged during the postexercise recovery; there was a concomitant increase in urinary DA excretion suggesting a specific release of this amine. NE and E may be designed to mobilize energy substrates, and possibly to contribute to the replenishment of muscular stores, but the role of DA is less understood. DA might act, as does NE, as a metabolic agent, or as a ganglionic neuromediator to prevent excessive NE release. We greatly appreciated the skillful Jacqueline Pequignot and Miss Colette Recherche Scientifique technicians. Received
23 March
1979; accepted
in final
technical assistance of Mrs. Gonnet, Centre National de la
form
16 May
1979.
REFERENCES 1. COTTET-EMARD, J. M. Etude du Mktabolisme des Cate’choZamines dans les urines de Rat. Aspects Technologiques et Dikte’tiques (thkse de doctorat). Lyon: Universitk Claude Bernard, 1978, p. 165. 2. COTTET-EMARD, J. M., AND L. PEYRIN. An improved fluorimetric method for assay of DOPA in urine and tissues and its use for determination of urinary DOPA, at endogenous level, in different species. J. Neural Transm. 41: 145-173, 1977. 3. DALMAZ, Y., AND L. PEYRIN. Specific ion-exchange chromatography and fluorimetric assay for urinary 3-0-methyldopamine. J. Chromatogr. 116: 379-394, 1976. 4. DALMAZ, Y,, AND L. PEYRIN. Occurrence of dopamine in the chromaffln tissue of a cartilaginous selachian fish: Scyliorhinus canicula. Comp. Biochem. Physiol. 59: 135-143, 1978. 5. DALMAZ, Y., AND L. PEYRIN. Rapid procedure for chromatographic isolation of DOPA, DOPAC, epinephrine, norepinephrine and dopamine from a single urinary sample at endogenous levels. J. Chromatogr. 145: 1 l-27, 1978. 6. DE SCHAEPDRYVER, A., AND M. HEBBELINCK. Ergometric exercise and urinary excretion of noradrenaline, adrenaline, dopamine, homovanillic and vanilmandelic acid. In: Biochemistry of Exercise, Medicine and Sport, edited by J. R. Poortmans. New York: Karger, 1969, p. 202-204. 7. GOODALL, MC C., AND H. ALTON. Urinary excretion of adrenaline metabolites in man during intervals of 2 minutes, 5 minutes and 10 minutes after intravenous injection of adrenaline. Biochem. Pharmacol. 14: 1595-1604, 1965. 8. HAGENFELDT, L., AND J. WAHREN. Turnover of free fatty acids during recovery from exercise. J. AppZ. Physiol. 39: 247-250, 1975. 9. HAGGENDAL, J., AND B. WERDINIUS. Dopamine in human urine during muscular work. Acta Physiol. &and. 66: 223-225, 1966. 10. HAVEL, R., B. PERNOW, AND J. NORMAN. Uptake and release of free fatty acids and other metabolites in the legs of exercising man. J. Appl. PhysioZ. 23: 90-99, 1967. 11. ISSEKUTZ, B., JR. Role of beta-adrenergic receptors in mobilization of energy sources in exercising dogs. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 44: 869-876, 1978. 12. JUCHMES, J., A. M. CESSION-FOSSION, AND M. FRANKIGNOUL. Comportement du systhme orthosympathique au tours de l’exercice musculaire chez l’homme. BUZZ. Sot. R. Sci. Lie’ge 7-8: 353-444, 1972. 13. KLEPPING, J., J. P. DIDIER, AND A. ESCOUSSE. Essai d’&aluation de la capacitb d’adaptation i l’effort par determination de l’hlimination urinaire des cat&holamines et de l’acide vanilmandblique. Rev. Suisse Med. Sport 14: 266-278, 1966. 14. KOPIN, I. J. Metabolic degradation of catecholamines. The relative importance of different pathways under physiological conditions and after administration of drugs. In: CatechoZamines, edited by H. Blaschko and E. Muscholl. Berlin: Springer, 1972, p. 270-282. 15. LIBET, B., AND T. TOSAKA. Dopamine as a synaptic transmitter and modulator in sympathetic ganglia: a different mode of synaptic action. Proc. Nat. Acad. Sci. USA 67: 667-673, 1970.
16. LISHAJKO, F. Dopamine secretion from the isolated perfused sheep adrenal. Acta Physiol. Stand. 79: 405-410, 1970. 17. MAAS, J. W., AND D. H. LANDIS. The metabolism of circulating norepinephrine by human subjects. J. PharmacoZ. Exp. Ther. 177: 600-612, 1971. 18. MATLINA, E. S. Main phases of catecholamine metabolism under stress. In: Catecholamines and Stress, edited by E. Usdin, R. Kvetpansky, and I. J. Kopin. New York: Pergamon, 1976, p. 353365. 19. NAFTCHI, N. E., G. F. WOOTEN, E. W. LOWMAN, AND J. AXELROD. Relationship between serum dopamine-/?-hydroxylase activity, catecholamine metabolism, and hemodynamic changes during paroxysmal hypertension in quadriplegia. Circ. Res. 35: 850-861, 1974. 20. NAZAR, K., Z. BRZEZINSKA, AND W. KOWALSKI. Mechanism of impaired capacity from prolonged muscular work following betaadrenergic blockade in dogs. Pfluegers Arch. 336: 72-78, 1972. 21. NEUVONEN, P. J., AND E. WESTERMANN. Studies on some metabolic effects of DOPA and dopamine in the rat. Naunyn Schmiedebergs Arch. Pharmacol. 284: 115-131, 1974. 22. PAGET, M., M. GONTIER, AND J. LIEFOOGHE. Recherches sur le dosage de la crbatinine urinaire. Ann. BioZ. CZin. 13: 535-553, 1955. 23. PEQUIGNOT, J. M., L. PEYRIN, R. FAVIER, AND R. FLANDROIS. Rkponse adrknergique & l’exercice musculaire intense chez le sujet skdentaire en fonction de l’bmotivitk et de l’entrainement. Eur. J. Appl. Physiol. Occup. Physiol. 40: 117-135, 1979. 24. PEYRIN, L., AND J. M. COTTET-EMARD. Automated specific fluorimetric methods for epinephrine and norepinephrine assay in a single biological extract. AnaZ. Biochem. 56: 515-531, 1973. 25. PEYRIN, L., J. M. COTTET-EMARD, AND B. CLAUSTRE. Improved automated procedure for urinary 3,4-dihydroxyphenylacetic acid (DOPAC) assay at nanomolar amounts. Biochem. Med. 19: 31% 343, 1978. 26. PEYRIN, L., J. M. COTTET-EMARD, F. JAVOY, Y. AGID, A. HERBET, AND J. GLOWINSKI. Long-term effects of unilateral 6-hydroxydopamine destruction of the dopaminergic nigrostriatal pathway on the urinary excretion of catecholamines (dopamine, norepinephrine, epinephrine) and their metabolites in the rat. Brain Res. 143: 567-572, 1978. 27. PEYRIN, L., AND Y. DALMAZ. La s&r&ion et l’inactivation pkriphbriques des cat&holamines (adrknaline, noradrbnaline, dopamine). J. PhysioZ. Paris 70: 353-433, 1975. 28. ROSENBLUM, R. Physiologic basis for the therapeutic use of catecholamines. Am. Heart J. 87: 527-530, 1974. 29. SNIDER, S. R., C. MILLER, A. L. N. PRASAD, V. JACKSON, AND S. FAHN. Is dopamine a neurohormone of the adrenal medulla? Naunyn Schmiedebergs Arch. Pharmacol. 297: 17-22, 1977. 30. THORNER, M. Dopamine is an important neurotransmitter in the autonomic nervous system. Lancet 1: 662-665, 1975. 31. VENDSALU, A. Studies on adrenaline and noradrenaline in human plasma. Acta Physiol. Stand. Suppl. 173: 57-68, 1960.
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PEQUIGNOT, J.M.,L. PEYRIN, M.H. MAYET,AND R. FLANMetabolic adrenergic changes during submaximal exercise and in the recovery period in man. J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 47(4): 701-705,1979.-The urinary excretion of dihydroxyphenylalanine (DOPA), catecholamines (CA) [ dopamine (DA), norepinephrine (NE), and epinephrine (E)], their 3-0-methylated derivatives [3-O-methyldopamine (3-MT), normetanephrine (NMN), and metanephrine (MN)], and their deaminated metabolites [dihydroxyphenylacetic acid (DOPAC) and vanilmandelic acid (VMA)] was studied in six healthy men, at rest, during short-term (15 min) or exhaustive submaximal exercise, and in the 2-h postexercise recovery period. During short-term exercise only NE and VMA excretions increased, whereas in postexercise period only DA output was enhanced. Exhaustive muscular work induced a rise in NE and E excretion during the test, and an increase in DA, NE, and NMN urinary levels during postexercise recovery, while the output of deaminated metabolites was unaltered. It is concluded that both release and synthesis of CA are stimulated by submaximal exercise, which induces, in addition to NE, a specific release of DA. A possible role of NE in lipid mobilization during recovery from exhaustive muscular work is evoked. The origin and role of released DA are also discussed. DROIS.
urinary catecholamines; postexercise recovery
dopamine;
adrenergic
metabolites;
MATERIALSANDMETHODS
Subjects
that the sympathoadrenal system is stimulated by muscular work, as shown by the enhanced levels of catecholamines (CA) in plasma and urine (6, 9, 12, 13, 23). Little attention has been paid to urinary excretion of CA metabolites during exercise (6, 13). Nevertheless, interesting knowledge about the functional activity of the adrenergic system may be drawn from study of the adrenergic urinary pattern, including CA, their precursors, and their metabolites (27). It is well known that body CA may be classified in two distinct pools, functional and tissue, with different metabolic pathways. It is now accepted that urinary CA and methoxyamines are related to the release activity of the adrenergic system (from the functional pool), whereas deaminated metabolites [dihydroxyphenyl acetic acid (DOPAC) and vanilmandelic acid (VMA)] are rather concerned with sympathetic and chromaffin intratissue events, including synthesis and storage of the CA tissue pool (17). In addition to norepinephrine (NE) and epinephrine (E), dopamine (DA) is normally present in urine and THERE IS EVIDENCE
0161-7567/79/0000-0000$01.‘25
plasma. Although DA is the immediate precursor in the synthesis of NE and E, both its origin and role remain to be discovered. Peripheral dopaminergic neurons have been described in sympathetic ganglia (15). Recently Snider et al. (29) have postulated that some noradrenergic fibers may release DA as neurotransmitter in stress circumstances. Moreover dopaminergic receptors are present in many peripheral tissues (30). Thus, it seems to be of interest to define the pattern of urinary DA excretion during heavy muscular work. The present study has been designed to determine the influence on the adrenergic and dopaminergic metabolism of submaximal exercise preformed either for 15 min or until exhaustion. To this end, we have studied the urinary excretion of the three CA (DA, NE, and E) and dihydroxyphenylalanine (DOPA), and their main metabolites, methyoxyamines [3-0-methyldopamine (3-MT), normetanephrine (NMN), and metanephrine (MN)] and deaminated metabolites, DOPAC and VMA, during the exercise period and in the postexercise recovery.
Copyright
0 1979 the American
Physiological
Six healthy male subjects voluntarily participated in the experiment. Their age, height, weight, and maximal oxygen uptake determined directly by gaseous exchange method averaged (mean t SE) 33 t 4 yr, 175 t 4 cm, 65 t 2kg, and 48.0 t 1.6 ml. kg-’ amin-‘, respectively. Experimental
Procedures
For exercise, the subjects pedaled a Monark cycle ergometer at a work load individually calculated to approximate 80% of their maximal oxygen uptake (VO, max). The trials were conducted around 2 P.M., at least 2 h after a light meal; the test was performed either for 15 min or until exhaustion (45-60 min). Except for exercise time, subjects were at rest in sitting or standing positions, and were advised to avoid strong mental activity; tobacco, coffee, and tea were not allowed. Moreover, to avoid emotional stress before the test, the subjects were progressively adapted by pedaling the bicycle ergometer on four separate occasions in the same conditions as those of the experiment. Urinary samples were collected during two consecutive 2-h periods before the ergometric work and subsequently Society
701
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702
PEQUIGNOT,
in two 2-h periods after the start of the exercise (Fig. 1). Each urine sample was acidified to pH 1 with 5 N HCl and stored at -25OC until analysis. Analytical
Procedures
For all the metabolites studied, analysis was performed on the total (free + conjugated) urinary content, except for VMA, which was studied in the free form. Hydrolysis was effected by boiling urinary samples at pH 1 for 10 min for DA, NE, E, DOPA, and DOPAC, and for 30 min for methoxyamines (3-MT, NMN, and MN). Determination of CA, DOPA, and DOPAC. To determine the CA (DA, NE, and E), DOPA, and DOPAC content in the 2Oml hydrolyzed urine sample the compounds were extracted by a double-step chromatographic procedure, involving purification on aluminum oxide and further separation on an Amberlite CG 50-NHJ+ column (5). In the eluates DA, NE, E, DOPA, and DOPAC were assayed according to the automated procedures developed in our laboratory: DA (1, 5), NE and E (24), DOPA (2), and DOPAC (25). Determination of methoxyamines. Methoxyamines (3MT, NMN, and MN) were extracted from 10 ml hydrolyzed urine by a double-step chromatographic procedure involving purification on Dowex 50 WXZ-H+ column and separation of the three above amines on Amberlite CG 50-NH4+ (3). In the final eluates, 3-MT, NMN, and MN were estimated by automated fluorimetric methods previously developed (1). Determination of VMA. Urinary VMA was extracted by means of ethyl acetate and analyzed by paper chromatography as described in a previous report (25). Determination of creatinine. Creatinine was determined according to the method of Paget et al. (22). Calculations Urinary excretion of CA or metabolites was expressed as ng or pg/mg of creatinine. The excretion rate of creatinine was unaffected by exercise whatever the duration might be (1,168 t 84 pgernin-’ at rest, 1,117 t 175 r_lg min-’ during short-term exercise, and 1,125 t 125 pg. min-’ during exhaustive exercise). Data were analyzed using a t test for paired observations and statistical significance was selected at P < 0.05. l
submaximal exercise
12
1 first urine collection I pre
FIG.
2 P.M.
second I urine collection
I
_ exercise periods
1. Schedule
representing
MAYET,
AND
FLANDROIS
RESULTS
Excretion of all compounds showed no change in the two successive urinary samples studied during the control preexercise periods. Thekefore, the exercise and postexercise data were compared to the mean control value of both preexercise periods. Fifteen-Minute
Exercise
Bouts
During the exercise period the sum of E, NE, and their metabolites (NE + NMN + E + VMA) increased 77% above control levels (ZCA in Table l), while the sum of DA metabolites (ZDA in Table 1) was unchanged. Urinary NE and VMA excretions were enhanced above baseline values by 49 and 83%, respectively (Figs. 2 and 3). No change in the urinary amounts of other metabolites was detectable. During the postexercise period the sums of amines and of methoxyamines @Met) remained elevated (Table 1) but urinary NE and VMA levels returned to base line and the output of E was significantly diminished (Figs. 2 and 3). In contrast, the sum DA + 3-MT was increased 63% (Table 1) and the urinary excretion of DA was enhanced 41% compared to resting levels (Fig. 2). Exhaustive
Exercise
Bouts
During the exercise period exhaustive muscular work resulted in much higher urinary excretion of NE (+ 112%) and E (+ 71%) (Fig. 2). A concomitant rise in the sum of methoxyamines (3 MT + NMN + MN) was noticed (+ 31% above preexercise levels) (ZMet in Table 2). Also the sum of amines (DA + NE + E) (Table 2) and the urinary output of DA (Fig. 2) tended to increase by 70 and 57%, respectively, but not significantly (P < 0.10). Surprisingly the concentration of each acid metabolite (DOPAC and VMA) in urine remained unchanged during prolonged exercise (Fig. 3). The urinary metabolic pattern of CA was strikingly altered during the postexercise period, as shown in Table 2 and Fig. 2 (compare to control). Both the sums of amines and of methoxyamines remained as elevated as during the exercise period (Table 2). Among these compounds, DA, NE, and MN concentrations remained at their exercise levels (Fig. 2), while 3 MT and NMN output was even more enhanced 82 and 45%, respectively, above basal rate (P < 0.10 and P < 0.05, respectively). DISCUSSION
1
10A.M.
PEYRIN,
6 P.M.
1 third urine collection
1 fourth urine collect I
I I exercise period general
I ion
1 postSexercise period
outline
of the study.
I
A constant fraction of CA secretion is found in urine, together with metabolites their excretion is apparent in a short delay after the release. From the results obtained by Goodall and Alton (7) after intravenous infusion of E, it may be assumed that 15-25% of the released amine appears in the urine 1 h after the adrenergic stimulation. On this basis, 2-h urinary collection periods were chosen to study the effects of submaximal exercise. Among urinary metabolites, CA and the corresponding 3-0-methylated derivatives are considered a satisfactory index of sympathoadrenal release activity; furthermore, because about 90% of the E originates from the adrenal
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METABOLIC
ADRENERGIC
1. Metabolic
TABLE
CHANGES
adrenergic
AND
EXERCISE
changes
induced
Control Camines CMet Cacids CCA CDA ZCA/ZDA DA + 3-MT NE + NMN E+MN CMet/Camines
1,198 432 8,200 4,584 5,297 0.902 1,155 310 164 0.398
703 by submaximal Exercise
t 305 t 52 t 1,500 t 889 -+ 961 k 0.182 t 314 t, 27 k 28 sfr 0.048
1,690 543 11,300 8,092 5,475 2.036 1,631 365 216 0.414
t t t t t t t t k t
short-term
exercise
A from Control
556 99 1,600 1,624 1,292 0.640 589 40 61 0.125
492 111 3,100 3,508 178 1.134 476 55 52 0.016
in healthy
Postexercise
t 307 t59 k 1,700 t 1,640* t 1,106 AI 0.701 t 329 t 27 t, 47 k 0.127
1,635 555 8,300 5,903 4,675 1.365 1,657 346 187 0.347
-+ k t t t t t t t t
men
Recovery
A from Control
258 82 900 1,011 495 0.294 295 45 34 0.042
438 123 100 1,319 622 0.463 502 36 23 0.051
t 206* t 38* t 1,300 t 1,211 zk 616 t 0.418 t 194* t 35 & 20 f: 0.059
Values are means t SE of urinary excretion of adrenergic and dopaminergic metabolites in ng/mg creatinine. Camines = DA + NE + E; CMet = 3-MT + NMN + MN; Cacids = DOPAC + VMA; CCA = NE + NMN + E + MN + VMA; CDA = DA + 3-MT + DOPAC. A, deviation from base-line values. See text for meanings of abbreviations. * Significantly different from zero, P c 0.05 (t test for paired observations; n = 6).
al .-‘c 320
.-
4J
; 240
0
PRE - EXERCISE
m
EXERCISE
m
POST-EXERCISE
NMN
c
1T
MN
DA. 10-l
depleted of striatal DA by locally injected 6-hydroxydopamine (6-OHDA) (26). DA has been found in the adrenal medullary secretion of some species (4% of total CA in the adrenal blood of sheep (16)). If this assumption may be extrapolated to man the DA amounts released from this source would be negligible compared to the high urinary excretion of DA in the basal state and, a fortiori, under adrenergic stimulation. DA is also associated with NE in most-sympathetic fibers and has been found at high levels in several tissues (lungs, bronchi, intestine, and carotid bodies) and in the small intensely fluorescent (SIF) cells of sympathetic ganglia (see for review Ref. 27). The relative contribution of these DA peripheral stores to urinary excretion is unknown; however, the SIF cells may represent interesting sources in this respect, since they are located inside the sympathetic ganglion very close to blood capillary vessels and they are able to release DA under preganglionic nerve stimulation (15). On the other hand, according to Snider et al.
)rg / mg creat
FIG. 2. Mean tSE urinary excretions of dihydroxyphenylalanine (DOPA), dopamine (DA), 3-o-methyldopamine (3-MT), norepinephrine (NE), normetanephrine (NMN) , epinephrine (E), and metanephrine (MN) in 6 men. Determinations were made on samples collected I) before exercise bouts (for each experiment, control value resulted from two successive urinary 2-h collections (preexercise periods: cZear bars)), 2) during a 2-h interval including a submaximal exercise (pedaling at a work load corresponding to 80% of maximal aerobic power) (exercise period: crosshatched bars), and 3) during a consecutive 2-h interval (postexercise period: stippled bars). Upper panel: short-term exercise bouts (15 min). Lowerpanel: exhaustive exercise bouts (45-60 min). See Fig. 1 for additional information. Significant differences from preexercise values indicated by *P < 0.05 (t test for paired observations;
n = 6).
medulla and 90% of the NE is furnished by sympathetic nerve endings (31), the estimation of E + MN and NE + NMN urine levels provides convenient parameters to analyze the relative activity of the glandular and neuronal adrenergic compartments (17). The origin of DA and 3-MT is unclear. Although very large amounts of DA are present in central dopaminergic neurons, it is very unlikely that urinary DA in man has a central origin, because we have not been able to demonstrate any change in DA excretion in rats unilaterally
inine
1-1
PRE-EXERCISE
LTq
EXERCISE
m
POST-EXERCISE
vMA short -term exefc ise 10 8
+
exhaustive lxercise
T
DOPAC short-term exercise
exhaustive exercise
6 4 2
FIG. 3. Mean tSE urinary excretions of vanilmandelic acid (VMA) and dihydroxyphenylacetic acid (DOPAC) in 6 men. Determinations were made on samples collected I) before the exercise bouts (for each experiment, the control value resulted from two successive urinary 2-h collections (preexercise periods: cZear bars)), 2) during a 2-h interval including a submaximal short-term, 15 min, or exhaustive, 45-60 min, exercise (pedaling at a work load corresponding to 80% of maximal aerobic power) (exercise period: cross-hatched bars), and 3) during a consecutive 2-h interval (postexercise period: stippled bars). See Fig. 1 for additional information. Significant differences from preexercise values indicated by *P < 0.05 (t test for paired observations; n = 6).
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704
PEQUIGNOT,
TABLE
2. Metabolic
adrenergic
changes induced
Exercise
Control Camines CMet Cacids CCA CDA XA/XDA DA + 3-MT NE + NMN E+MN XMet/Xamines Values Table 1.
1,066 361 10,900 6,185 6,133 1.195 960 274 96 0.536
t t t t t t t, t -+ t,
by submaximal
373 94 1,300 1,280 1,015 0.322 415 63 18 0.189
are means t, SE of urinary excretion * Significantly different from zero,
1,711 474 10,500 5,662 7,117 0.765 1,641 377 167 0.345
t 405 t 114 t, 1,800 t 1,398 -+ 929 t 0.133 k 391 t, 58 t 55 t 0.084
exhaustive A from Control 644 113 380 523 984 0.430 681 103 71 0.191
PEYRIN,
MAYET,
AND
exercise in healthy
men
Postexercise
t 355 t 35* -+ 1,360 t 606 t, 1,034 t, 0.223 t 430 t 38* t38 t 0.226
of adrenergic and dopaminergic metabolites in ng/mg P < 0.05 (t test for paired observations; n = 6).
(29), under severe stress some noradrenergic neurons might become partially dopaminergic, due to the relatively limited capacity of the cell to synthesize NE from DA, and might thus release DA. With regard to deaminated CA metabolites present in urine, there is evidence that they are related to intraneuronal or intrachromaffin metabolism by monoamine oxidase, and may reflect intense synthesis activity overpassing storage capacities (14, 17). VMA is formed both in the adrenal gland and in sympathetic neurons from E and/or NE. DOPAC is an important metabolite of DA (25), but no precise informati0.n about its topographic origin is available. In the present investigation, it appears that exhaustive submaximal exercise (80% VOW max) alters markedly the urinary metabolic pattern of CA, both during and after the test, while smaller changes are induced by short-term submaximal work. In accordance with previous studies (12, 13), we observed during the 15min exercise bouts, an increase in NE excretion (Fig. 2), which certainly originated from sympathetic nerve endings. Under the same conditions, we previously observed a rise in plasma E in addition to NE (23), whereas in the present study urinary excretion of E failed to increase (Fig. 2). As the absolute increase of E is generally smaller than that of NE (23), measurements in a 2-h urine collection may not detect short changes in the plasma concentrations of E. Moreover, the enhanced urinary VMA level (Fig. 3) seems to indicate that the synthesis of CA was stimulated by shortterm submaximal exercise. This is in line with the finding that in rats moderate exercise prolonged for 2.5 h led to an activation of CA synthesis in adrenals and heart (18). The exhaustive exercise has acute effects on the urinary metabolic pattern of NE and E. The increased excretion of these amines (Fig. 2) was not due to changes in the catechol-O-methyltransferase activity because the ratio of methoxyamines to amines remained unchanged (Table 2). Contrary to observations of the 15min test, VMA excretion during the exhaustive exercise period was unaltered (Fig. 3). This unchanged VMA excretion, together with the active release of CA may indicate that, in the exhaustive conditions, the strong stimulation of CA secretion surpasses the capacities of intraneuronal storage of newly synthetized CA. In other words, both release and synthesis processes are stimulated by exercise, but CA are released as soon as they are formed.
1,571 558 11,400 7,632 6,015 1.341 1,562 420 147 0.371
t & I!I t t t k t, t t
FLANDROIS
Recovery
A ‘from Control
415 182 2,400 2,965 566 0.517 439 106 47 0.071
505 197 540 1,447 119 0.145 602 146 51 0.165
creatinine.
Abbreviations
t 87* t 99 -+ 1,800 zk 2,051 t 882 t 0.51 t 109* t 59* t29 t 0.193
as indicated
in
There is evidence to suggest that CA are important the energy substrate mobilization factors in controlling from endogenous stores during exercise. Indeed P-adrenergic blockade by propranolol is able to inhibit totally the exercise-induced lipolysis, partially the glycogenolysis in dogs, (11) and alter the working capacity (20). Furthermore, we have found that, in man, the exerciseinduced release of CA (NE and E) was enhanced by fasting and was significantly correlated to the blood levels of energy substrates (glucose, lactate, and glycerol) (Pequignot, Peyrin, and Peres, unpublished observation). In the-present-study, another striking effect of submaximal exhaustive work was the sustained elevated excretion of NE and its metabolite NMN during the postexercise recovery (Fig. 2, Table 2), demonstrating a prolonged system. Hagenfeldt and activation of the adrenergic Wahren (8) have reported th .at the fre le fatty acid release into plasma is raised during recovery from exercise. Accordingly, it can also be reasonably assumed from the present results that in the period following the prolonged muscular work the increased sympathetic activity would control lipid mobilization. Thus, because the muscle pool of triglycerides is mobilized during the muscular work (lo), NE would possibly contribute to the restoration of the lipidic muscular stores after the exhaustive test. Naftchi et al. (19) noted a concomitant release of DA and NE in quadriplegic subjects during hypertensive stress. In the present study the submaximal exercise was able to induce a large release of DA in the postexercise period in addition to NE in healthy men. This was shown by the rise in urinary excretion of DA (Fig. 2) and by the increased sum DA + 3-MT (Tables 1 and 2). DA is generally considered as a precursor for NE in the peripheral adrenergic system. However, the concomitant increase in DA and NE in this study does not seem to result from exhaustion of NE endogenous stores leading to DA accumulation, as the release of NA remained at a very high level during and after the exhaustive exercise (Fig. 2). Thus, there is evidence that the release of DA is specific; however, its origin cannot be assessed. The role of DA in the working performance and in the postexercise recovery is less clear than that of other CA. DA, like NE, is able to exert metabolic effects on carbohydrate and lipid stores (21). In the cardiovascular field, DA is a less hypertensive agent than NE but exhibits a particular vasodilating action on the splanchnic, renal, and coronary vascular bed (28). On the other hand, in sympathetic
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METABOLIC
ADRENERGIC
CHANGES
AND
705
EXERCISE
ganglia, it has been shown that DA from SIF cells is able neurons and to to depress the activity of sympathetic inhibit NE release (15). In agreement with this knowledge, and with the fact that DA release was especially evident in the recovery period after short-term as well as after exhaustive exercise (Fig. 2)) the role of the increased release of DA o bserved in our study might be to enhance the metabolic effects of other CA or, conversely, to regulate NE release to reduce the neuromediator losses. Alternatively, both types of action might occur simultaneously, but it cannot be decided which of these mechanisms would be predominant. In conclusion, the submaximal exercise was able to induce changes in urinary metabolic pattern of CA, indicating increased synthesis and release of these neuro-
hormones. After exhaustion, the secretion of NE was prolonged during the postexercise recovery; there was a concomitant increase in urinary DA excretion suggesting a specific release of this amine. NE and E may be designed to mobilize energy substrates, and possibly to contribute to the replenishment of muscular stores, but the role of DA is less understood. DA might act, as does NE, as a metabolic agent, or as a ganglionic neuromediator to prevent excessive NE release. We greatly appreciated the skillful Jacqueline Pequignot and Miss Colette Recherche Scientifique technicians. Received
23 March
1979; accepted
in final
technical assistance of Mrs. Gonnet, Centre National de la
form
16 May
1979.
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