Glucoregulatory and hormonal responses to repeated bouts of intense exercise in normal male subjects ERROL B. MARLISS, EMMANUEL SIMANTIRAKIS, PHILIP D. G. MILES, CAMERON PURDON, REJEANNE GOUGEON, CATHERINE J. FIELD, JEFFREY B. HALTER, AND MLADEN VRANIC McGill Nutrition and Food Science Centre, Royal Victoria Hospital, Montreal, Quebec H3A 1Al; Departments of Physiology and Medicine, University of Toronto, Toronto, Ontario M5S lA8, Canada; and Department of Internal Medicine and Institute of Gerontology, University of Michigan and Veterans Administration Medical Center, Ann Arbor, Michigan 48109

MARLISS, ERROL B., EMMANUEL SIMANTIRAKIS, PHILIP maximal oxygen consumption (VO, m,), our group (10, D.G. MILES,CAMERONPURDON,RI?JEANNEGOUGEON,CATH- 27, 33, and unpublished observations) and others (4, 13, ERINEJ. FIELD,JEFFREY B. HALTER,AND MLADEN~RANIC. 17) have shown that a period of hyperglycemia superGlucoregulatory and hormonal responses to repeated bouts of invenes immediately upon exhaustion after a single bout or tense exercise in normal male subjects. J. Appl. Physiol. 71(3): repeated bouts in rapid succession (22). This is accompa924-933,1991.-Glucose turnover and its regulation were studnied by considerable hyperinsulinemia that persists to ied during and after two identical bouts of intense exhaustive beyond 40 min in lean (17,24,27,33) subjects and is more exercise separated by 1 h to define differences in response. Six intense and prolonged in obese (20, 33) subjects. lean young postabsorptive male subjects exercised at -100% We recently showed, using a stepped tracer infusion maximal 0, uptake (3.7 t 0.3 l/min) for 13.0 t 0.7 min for the method (9, 25), that this postexercise hyperglycemia is first (EXl) and 13.2 t 0.8 min for the second (EX2) bout. Plasma glucose increased during EXl and peaked at 7.0 t 0.6 due to a considerably larger increase in glucose producmmol/l in early recovery but to 5.8 t 0.5 mmol/l (P < 0.05) tion (Ra) than of utilization (Rd) during exercise that after EX2, and both the hyperglycemic and the hyperinsulinalso persists into the early phase of recovery despite the emit responses were less after EX2 (P < 0.015, analysis of varirapid and large hyperinsulinemic response (24). This was ance). The hyperglycemia was due to lesser increments in glufollowed by a more prolonged period of Rd slightly excose utilization (Rd) (3-fold resting) than glucose production ceeding Ra as both approached preexercise values and (Ra) (7-fold) toward exhaustion and for 7 min of recovery. The accounted for the return to preexercise plasma glucose rise in Rd was more rapid (P < 0.05) and metabolic clearance concentrations. This has previously been reported for rate was greater during (P = 0.015) and from 9 to 60 min after steady-state 85% VO, maxexercise (4) and for a stepwise EX2, and Ra also remained higher during recovery (P < 0.05). increase in work load to 100 and 110% VO, m8x levels (17). Marked and similar increments in plasma norepinephrine (18fold) and epinephrine (I4-fold) occurred with both bouts. We postulated that this physiological response is approPlasma glucagon increments were small and not different. priate to repletion of the muscle glycogen mobilized durTherefore, I) more circulating glucose was used with EX2, 2) ing exercise but that sustained hyperglycemia in the presgreater metabolic clearance rate during and after EX2 suggests ence of hyperinsulinemia would imply relative muscle local muscle adaptations due to EXl, and 3) significant correlaunresponsiveness to the insulin. tions (P < 0.002) between plasma norepinephrine and Ra (r = This pattern of increase in Ra, as well as the period of 0.82) and Ra - Rd (r = 0.52) and between epinephrine and Ra Ra > Rd, corresponded in time to that of the responses of (r = 0.71) and Ra - Rd (r = 0.48) suggest a major regulatory plasma catecholamines, which we (24) and others (4,17) role for the catecholamine responses. glucose turnover;

insulin;

catecholamines;

glucagon

MAJOR DIFFERENCESEXIST in the control of glucoregulation in humans during exercise and postexercise recovery periods in relation to the intensity and duration of exercise (11, 30). With mild and moderate exercise in which glucose production is precisely matched to utilization (except for very prolonged exercise), no changes in plasma glucose concentration occur, and the suppressed plasma insulin concentrations promptly return to preexercise levels (11,29,34,35). Glucagon responses are modest but important because of the fall in insulin (11, 29, 30). In contrast, after intense exercise, e.g., >80% of 924

postulated as the prime mediators of these glucoregulatory responses. Furthermore we hypothesized that, given the glycogen depletion from the first exercise bout and the hormone-substrate milieu of the 1st h of recovery, a second bout of the same intensity should be associated with a different set of exercise and postexercise metabolic responses. These might include a greater requirement for blood-borne energy substrates during exercise and a greater supply for recovery period muscle glycogen repletion. The present study was designed to elucidate such responses.

MATERIALS AND METHODS Subjects and procedures. Six lean fit weight-stable healthy young male adult subjects participated in the

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1. Subject characteristics Le, Yr Height, m Weight, kg Body mass index, kg/m2 VO 2 max, llmin Study work load, W Plasma glucagon, rig/l* Plasma norepinephrine, nmol/l* Plasma epinephrine, pmol/l*

Values are means sured in overnight-fasted cise bout.

6 25.5k1.4 1.68_tO.O6 74.5t1.8 26.6k1.8 3.7t0.3 223t28 432232 1.37kO.13 193*29

t SE. VO, -, maximal 0, consumption. * Meastate, in seated position, before the first exer-

study. They were informed of the purpose of the study and the possible risks of the exercise, cannulations, blood sampling, and tritiated glucose administration. They gave consent as prescribed by the institutional Human Ethics Committee. The screening before the study included medical history, physical examination, hemogram, blood biochemistry, urinalysis, electrocardiogram, and chest roentgenogram. Their anthropometric and work load data are presented in Table 1. Their Vozrnax was determined during an incremental work load test on an electrically braked cycle ergometer (Quinton Instrument, Seattle, WA) during which resistance was increased by 100 kpm/min (100 kpm = 16.3 W) each minute until exhaustion. Breath-by-breath gas analyses were performed continuously with a cardiopulmonary exercise system (Medical Graphics, St. Paul, MN). During the incremental exercise test, the subjects breathed through a Hans Rudolph low-resistance valve with a dead space of 95 ml. Oxygen uptake (VO,, STPD), carbon dioxide output #CO,, STPD), ventilation (VE, I/ min BTPS), and respiratory exchange ratio (RER) were calculated and recorded at l-min intervals. The heart rate was displayed electrocardiographically. On a separate occasion 22 days after the VO, maxtest, each subject underwent a test without blood sampling at 50% for 30 s, followed by ~80% of the previously established maximum work load to determine that the time to exhaustion would be lo-15 min. The work load that achieved this end point was then used for the study involving glucose turnover measurements. The mean study work load was 223 t 28 W, an d w h ere VO, measurements were made (n = 3), by exhaustion the vo2 approached 100% of the previously determined maximum, because it tends to increase with time at high work loads, although resistance is constant. At 0800-0900 in the 12-h overnight-fasted (postabsorptive) state, the subjects presented themselves to the laboratory without having undergone significant exercise for the previous day. A 20-gauge Cathlon IV cannula (Critikon Canada, Markham, Ontario, Canada) was inserted into one antecubital vein for blood sampling and another into a forearm vein of the other arm for infusion. The subjects remained sitting with the catheters being kept patent by a slow infusion of 0.9% saline. After 20-30 min, a preinfusion blood sample was drawn, and the infusion of [3H]glucose (Amersham Canada, Oakville, Ontario, Canada) was begun. A priming bolus of 11 ml was followed bv a constant infusion at 0.109 ml/min of a solu-

925

EXERCISE

tion containing 2 &i/ml in 0.9% saline for 150 min. Blood was sampled at 90,100,110,120,130,140, and 150 min to ensure a steady state of enrichment of plasma [3H]glucose. The rate of infusion was doubled during exercise and then returned to the original rate at exhaustion, as reported elsewhere (24), a method that prevents the decline in tritiated glucose-specific activity during exercise. A sample was drawn at exhaustion, and this time was defined as time 0 of recovery, such that samples were drawn at 2,4, 6,8, 10, 15,20,30,40,50, and 60 min thereafter for glucose and radioactivity measurements. Then a second identical exercise bout was begun, again with doubling of tracer infusion rate and increased frequency of sampling up to 10 min of recovery; sampling continued until 60 min of recovery. Duration of the first exercise bout was 13.0 t 0.7 (SE) min and that of the second was 13.2 t 0.8 min. Sampling was less frequent for insulin, glucagon, catecholamines, and lactate and pyruvate measurements, as shown in Figs. l-7 and Table 2. Samples for glucose turnover measurements were placed into tubes that contained heparin and sodium fluoride and were processed as previously described (34). Heparinized plasma was collected with aprotinin (Trasy101,10,000 kallikrein inhibitor U/ml, FBA Pharmaceuticals, New York, NY) in a volume 1110th that of the added blood for subsequent insulin and glucagon assays. For catecholamine measurements, blood was added to EGTA- and reduced glutathione-containing tubes, and the plasma was immediately deproteinized with 2 mol/l perchloric acid and frozen at -7OOC until assay. One aliquot of whole blood was immediately deproteinized in an equal volume of cold 10% (wt/vol) perchloric acid and kept on ice until centrifuged at 4°C for later lactate and pyruvate assay. Except where otherwise specified, plasma or supernatants were kept at -2OOC until assay. Analytic methods. Plasma glucose was measured by the 2. Blood lactate and pyruvate during intense exercise and recovery TABLE

Lactate, mm01 11 First

Pyruvate, mmol/l exercise

Lactate/Pyruvate

bout

-10 min 0 min Exhaustion Recovery 4 min 10 min 20 min 40 min 60 min

0.71t0.07 0.78kO.09 13.2t1.13*

0.048&0.005 0.053t0.005 0.175t0.009*

14.8t0.45 14.6t0.37 77.2&9.6*

12.9t0.84* 10.6t2.36* 6.83&0.80* 3.25t0.38* 1.87t0.19*

0.297t0.046* 0.31 lt0.063* 0.299&0.062* 0.182&0.014* 0.129t0.012*

47.6t5.8” 38.5t4.7* 30.9&10.4* 17.6&1.09* 14.6t0.81

Exhaustion Recovery 4 min 10 min 20 min 40 min 60 min

12.6t0.84*

0.261&0.023*

49.5t4.7*

11.3t0.93* 7.98*0.59* 5.09t0.60* 2.38t0.20* 1.57t0.13

0.419t0.035* 0.392t0.035* 0.260&0.042* 0.138t0.028 0.082&0.016*

27.5t2.9* 20.6kl.O” 2l.lt2.5* 27.5k12.8 23.7t5.1

Second

exercise

bout

Values are means rfr SE; n = 6. * P c 0.01 vs. corresponding time 0 value for first exercise bout and 60-min value for second exercise bout. Statistics for comparisons of responses between bouts are given in the text.

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glucose oxidase method with the use of a Beckman Glucose Analyzer II (Beckman Instruments, Fullerton, CA). Blood lactate and pyruvate were measured by two-channel automated enzymatic microfluorimetric methods, enabling assay of replicate 5- or lo-p1 aliquots of the perchloric acid supernatants, and with the use of two Turner model 430 spectrofluorometers (Sequoia-Turner, Mountain View, CA) (21). Plasma insulin was determined by radioimmunoassay (RIA) with the use of an anti-beef insulin serum, purified human insulin standard (27.3 pU/ng), and 1251-labeled pork insulin (Novo Research Institute, Gentofte, Denmark); dextran-coated charcoal was used to separate free and bound hormone. Plasma glucagon was measured by RIA with the use of purified porcine glucagon standard, monoiodinated 1251-labeled pork glucagon (Novo Research Institute), antiserum 04A provided by Dr. R. H. Unger (Dallas, TX), and the same separation procedure. A blank without antibody was run with each sample to determine nonspecific binding. All assays performed on aprotinin-containing plasma were corrected for the plasma dilution introduced, by the concurrently obtained hematocrit. Plasma norepinephrine and epinephrine concentrations were measured with the use of a radioenzymatic technique (7). The sensitivity of this method is ~50 pmol/l. The intra- and interassay coefficients of variation for all assays were