00l3-7227/90/1273-1160$02.00/0 Endocrinology Copyright © 1990 by The Endocrine Society
Vol. 127, No. 3 Printed in U.S.A.
FATMA HREASH, LANNY C. KEIL, LANCE CHOU, AND IAN A. REID Department of Physiology (F.H., L.C., I.A.R.), University of California, San Francisco, San Francisco, CA 94143-0444; and Ames Research Center (L.C.K.), Moffett Field, CA 94035
ABSTRACT. Experiments were performed in conscious rabbits with sectioned aortic depressor nerves to determine whether there is an interaction between angiotensin II (Ang II) and the baroreceptor reflexes in the control of arginine vasopressin (AVP) secretion. Baroreceptor reflexes were activated by a 5- or 10-min period of bilateral carotid occlusion with or without background infusion of Ang II at 10 or 20 ng/kgmin. Carotid occlusion increased mean arterial pressure, right atrial pressure, and heart rate, but did not change plasma AVP (PAVP) concentration. Infusion of Ang II at 10 ng/kgmin increased PAVP from 4.0 ± 0.9 to 6.3 ± 1.8 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion produced the same cardiovascular changes as before Ang II, but still failed to increase PAVP.
I
N ADDITION to its well-established roles in the regulation of arterial pressure, aldosterone secretion, and renal function (1), angiotensin II (Ang II) has been implicated in the control of arginine vasopressin (AVP) secretion (2, 3). Several investigators have observed that systemic administration of Ang II can increase AVP release, although there is still debate concerning the sensitivity, magnitude, and physiological significance of this effect (2, 3). There are also questions concerning the mechanism by which Ang II increases AVP release. There is evidence for a direct action on the brain that is mediated via the subfornical organ or another circumventricular organ (2, 3). However, it is also possible that Ang II can increase AVP release by interacting with baroreceptor reflex mechanisms. This proposal is based on two sets of observations. First, it is known that both the low and high pressure baroreceptors play important roles in the control of AVP secretion (4). Second, there is considerable evidence that Ang II can interact with the baroreceptor reflexes to modulate the reflex control of heart rate (HR) Received January 5, 1990. Address all correspondence and requests for reprints to: Dr. Ian A. Reid, Department of Physiology, S-762, University of California, San Francisco, California 94143. * This research was supported by NIH Grant HL-29714.
Because increased atrial pressure can inhibit AVP secretion, the experiments were repeated in acutely vagotomized rabbits. Vagotomy increased heart rate but did not change mean arterial pressure or PAVP. Carotid occlusion after vagotomy increased PAVP from 2.2 ± 0.2 to 3.3 ± 0.5 pg/ml (P < 0.05). Ang II infusion again increased PAVP but did not enhance the AVP response to carotid occlusion (2.9 ± 0.4 to 3.9 ± 0.7 pg/ml). These results provide further evidence for a role of the carotid sinus baroreceptors and vagal afferents in the control of AVP secretion and demonstrate that Ang II stimulates AVP secretion in rabbits. However, they do not reveal any interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. {Endocrinology 127: 1160-1166, 1990)
and sympathetic nerve activity such that both are maintained at higher levels for any given level of arterial pressure (3, 5, 6). The aim of the present investigation was to determine whether there is an interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. This was accomplished by investigating the effect of bilateral carotid occlusion alone, and in combination with Ang II, on plasma AVP concentration in conscious, aortic depressor-nerve sectioned rabbits. Carotid occlusion was selected as a stimulus to AVP secretion because it has been reported to increase AVP secretion in rabbits in which the aortic depressor nerves have been sectioned (7). It was reasoned that if there is an interaction between Ang II and the baroreceptor reflexes, the combination of Ang II and carotid occlusion should produce an increase in AVP secretion that is greater than the sum of the responses to the two stimuli alone.
Materials and Methods The experiments were performed on male New Zealand White rabbits weighing 2.5 to 4.0 kg (Nitabel, Haywood, CA). Standard commercial diet (Purina Rabbit Chow, St. Louis, MO) and tap water were available ad libidum. The experiments were conducted in accordance with the University of California, San Francisco Committee on Animal Research. 1160
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
Effects of Carotid Occlusion and Angiotensin II on Vasopressin Secretion in Intact and Vagotomized Conscious Rabbits*
ANG II, BARORECEPTORS, AND AVP SECRETION Surgical procedures
Experimental protocols On the day of an experiment, rabbits were brought to the laboratory and loosely restrained in a covered stainless steel cage. Pulsatile arterial pressure, mean arterial pressure (MAP), HR, and, in some rabbits, RAP were recorded continuously throughout the experiment using Cobe transducers (Cobe Laboratories, Inc., Lakewood, CO) and a cardiovascular monitor. Cardiovascular data were simultaneously recorded on a Grass Polygraph (Grass Instruments, Quincy, MA) and digitized and stored on a PDP 11/23 Plus computer (DEC, Maynard, MA). Blood samples (vol, 2.0 ml) were collected via the femoral artery catheter and replaced with an equal vol of sterile isotonic saline. The samples were placed in chilled centrifuge tubes containing 0.2 ml 0.3 M EDTA and centrifuged at 4 C, and the plasma was frozen for the subsequent measurement of plasma AVP concentration by RIA (8). Before experiments were started, the rabbits were allowed at least 30 min for blood pressure and HR to stabilize. After control measurements had been made, both carotid arteries were occluded for 5 or 10 min by inflating the vascular occluders. This was followed by a 15-min recovery period during which blood pressure and HR returned to their preocclusion values. An infusion of Ang II (Peninsula Laboratories, Belmont, CA) (10 or 20 ng/kg-min) or saline was started, and 20 min later a second bilateral carotid occlusion was performed. Blood samples were collected at the end of each protocol period. The following groups of experiments were performed.
Exp 1. With vagus nerves intact, six rabbits underwent bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min). Six others underwent bilateral carotid occlusion (5 min) and saline infusion (0.0136 ml/min). Another six rabbits underwent bilateral carotid occlusion (5 min) and Ang II infusion (20 ng/ kg-min). The last group of six rabbits underwent bilateral carotid occlusion (10 min) and Ang II infusion (10 ng/kg-min). Exp 2. Acute vagal blockade with lidocaine was performed on six rabbits. After control measurements had been made, 3 ml 2% lidocaine were applied to the perivagal region. A blood sample was collected 5 min later, and after another 5 min, the effects of bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min) were tested. Sham vagal blockade was performed on three rabbits. This protocol was identical to that for acute vagal blockade just discussed except that 0.9% saline was administered instead of lidocaine. Two rabbits underwent surgical vagotomy and, six to 8 h later, the effects of bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min) were studied as described in Exp 1. Blood pressure and HR data are presented as computergenerated means. In general, data were averaged over a 2- to 10-min period. With carotid occlusion, data collected during the last 2 to 3 min of the occlusion period were averaged. All data are expressed as the mean ± SE. Statistical evaluation of the data was performed using one- or two-way analysis of variance for repeated measures and the Neuman-Keuls multiple-range test. Where appropriate, the paired t test was also used. Changes were considered to be statistically significant when P < 0.05.
Results Effects of carotid occlusion and Ang II in rabbits with intact vagi The effects of a 5-min period of bilateral carotid occlusion before and after infusion of Ang II at 10 ng/kg-min are summarized in Fig. 1. During the first carotid occlusion, MAP increased from 82.2 ± 6.4 to 133.1 ± 8.9 mm Hg (P < 0.05), and HR increased from 257 ± 11 to 300 ± 9 beats/min (bpm) (P < 0.05). Plasma AVP (PAVP) concentration did not change significantly (4.0 ± 1.0 to 3.9 ± 0.9 pg/ml). MAP and HR rapidly returned to their control values after release of the occlusion. Infusion of Ang II increased MAP from 82.7 ± 6.4 to 97.4 ± 7.4 mm Hg (P < 0.05) but did not change HR (262 ± 12 to 262 ± 13 bpm). PAVP increased from 4.0 ± 0.9 to 6.3 ± 1 . 8 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion caused a further increase in MAP to 146.4 ± 8.3 mm Hg (P < 0.05) and increased HR to 305 ± 9 bpm (P < 0.05). These changes in MAP and HR were almost identical to those produced by carotid occlusion before Ang II. Carotid occlusion during Ang II infusion did not cause any further change in PAVP (6.3 ± 1.8 to 6.1 ± 2.0 pg/ml). Infusion of the saline vehicle had no effect on MAP, HR, or PAVP, and did not alter the responses to carotid occlusion (Fig. 1).
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
The rabbits were premedicated with acepromazine maleate (Promace, Aveco Co., Fort Dodge, IA) (2 mg/kg im) and anesthetized with sodium pentobarbital (25 mg/kg iv). Under sterile conditions, a Tygon catheter (0.04 inch id) was inserted into a femoral artery for blood pressure recording and blood sampling. Two Tygon catheters (0.03 inch id) were inserted into the left jugular vein for iv infusions. In some animals, one of the jugular catheters was advanced into the right atrium for recording right atrial pressure (RAP). In all animals, both aortic depressor nerves were identified and sectioned at their junction with the vagal and superior laryngeal nerves. The carotid arteries were isolated, and an inflatable balloon vascular occluder (2 mm id, In Vivo Metric, Healdsburg, CA) was placed around each artery without interfering with blood flow. In six rabbits, another two vascular occluders with punctured balloons were placed around the carotid arteries and associated vagus nerves. These were used to produce acute, reversible vagal blockade by local application of lidocaine. The catheters and occluders were tunneled sc, exteriorized dorsally between the scapulae, and protected by a nylon jacket (Medical Arts, Los Angeles, CA). Catheters were flushed every other day with sterile isotonic saline and filled with heparinized saline. The rabbits were treated with penicillin (Penicillin G Procaine, Hanford Co., Syracuse, NY) (300,000 U/day im) for 2 days after surgery. They were allowed to recover for at least 2 days before experiments were begun. Two rabbits were subsequently anesthetized with Brevital sodium (5-10 mg/ kg iv), and both vagus nerves were sectioned in the cervical region caudal to the junction with the superior laryngeal nerves. These animals were studied 6-8 h later (see below).
1161
1162
ANG II, BARORECEPTORS, AND AVP SECRETION
Endo • 1990 Vol 127 • No 3
•
All
Saline
170 150 •
130 •
ARTERIAL PRESSURE (mmHg)
110
•
320
FIG. 1. Effects of bilateral carotid occlusion (BCO) (5 min) on MAP, HR, and PAVP concentration before and during infusion of Ang II (All) (10 ng/kg-min) or saline. Bars indicate the mean ± SE of observations made in six rabbits.
280 -
HEART RATE (bpm)
260 •
240 •
220
10.0
8.0
6.0
PLASMA AVP CONC. (pg/ml)
4.0
2.0
0.0
Control
BCO
Control
All
AII+BCO
TREATMENT
The effects of a 5-min period of carotid occlusion before and during infusion of Ang II at 20 ng/kg-min are summarized in Fig. 2. The effects of carotid occlusion before Ang II were almost identical to those shown in Fig. 1. Infusion of Ang II increased MAP from 84.5 ± 4.7 to 100.6 ± 6.4 mm Hg (P < 0.05), but did not change HR. PAVP increased from 3.1 ± 0.7 to 5.3 ± 1.0 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion again increased MAP and HR, but did not change PAVP. The effects of a 10-min period of carotid occlusion and infusion of Ang II at 10 ng/kg-min on MAP, HR, and RAP are shown in Fig. 3. Carotid occlusion caused increases in MAP and HR similar to those shown in Figs. 1 and 2, and increased RAP from -0.8 ± 1.2 to 1.7 ± 1.5 cm H2O (P < 0.05). Ang II increased MAP and PAVP (3.0 ± 0.3 to 3.5 ± 0.4 pg/ml, P < 0.05) but did not change HR or RAP. The hemodynamic responses to
carotid occlusion during Ang II infusion were similar to those before Ang II, and again PAVP did not change. Effects of uagotomy
A representative record showing the cardiovascular responses to bilateral carotid occlusion after vagal blockade with lidocaine is shown in Fig. 4. The effects of vagal blockade with lidocaine (n = 6) and surgical vagotomy (n = 2) were similar, and the data were combined into one group for analysis (Fig. 5). After vagotomy, HR increased from 272 ± 6 to 310 ± 14 bpm (P < 0.05). MAP tended to increase but not significantly (80.9 ± 2.1 to 88.7 ± 4.6 mm Hg). PAVP did not change significantly (1.9 ± 0.2 to 2.2 ± 0.2 pg/ml). Carotid occlusion after vagotomy increased MAP from 88.7 ± 4.6 to 120.3 ± 3.7 mm Hg (P < 0.05). There were small increases in HR in
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
MEAN
ANG II, BARORECEPTORS, AND AVP SECRETION
1163
120
MEAN ARTERIAL PRESSURE (mmHg)
100 •
320
100
80
320 r
r
300
HEART RATE (bpm)
HEART RATE (bpm)
280
260 •
260
PLASMA AVP CONC. (pg/ml)
RIGHT ATRIAL PRESSURE (cmH20)
Control
All
TREATMENT
FIG. 2. Effects of bilateral carotid occlusion (BCO) (5 min) on MAP, HR, and PAVP concentration before and during infusion of Ang II (All) at 20 ng/kgmin. Bars indicate the mean ±SE of observations made in six rabbits.
all animals; the overall change was from 310 ± 14 to 330 ± 16 bpm (P < 0.05). RAP increased from -1.3 ± 0.7 to 4.5 ± 0.7 cm H2O (P < 0.05). PAVP increased from 2.2 ± 0.2 to 3.3 ± 0.5 pg/ml (P < 0.05). Infusion of Ang II increased MAP and PAVP without changing HR or RAP. Carotid occlusion during Ang II infusion produced increases in MAP, HR, RAP, and PAVP that were not significantly different from those before Ang II. Sham vagotomy had no effect on any of the measured variables and did not alter the cardiovascular or AVP responses to carotid occlusion and Ang II (Fig. 5).
Discussion Bilateral carotid occlusion is a convenient and effective method of activating baroreceptor reflexes, particularly when the buffering effect of the aortic arch baroreceptors
-2
Control
BCO
Control
All
AII+BCO
TREATMENT
FIG. 3. Effects of bilateral carotid occlusion (BCO) (10 min) on MAP, HR, and RAP before and during infusion of Ang II (All) at 10 ng/kgmin. Bars indicate the mean ±SE of observations made in six rabbits.
is eliminated by sectioning the aortic depressor nerves (9, 10). In the present study, carotid occlusion produced marked increases in arterial pressure and HR similar to those observed in other studies (9, 10). On the other hand, carotid occlusion failed to increase PAVP concentration. The same result was obtained whether the period of carotid occlusion was 5 or 10 min. The failure of carotid occlusion to increase PAVP concentration was unexpected in view of the report by Courneya et al. (7) that reduced carotid sinus pressure increased PAVP concentration in aortic depressor nerve sectioned rabbits. The reason for the difference between the present results and those of Courneya et al. is not clear but is probably related to differences in experimental design. For example, in the study by Courneya et al. (7), the rabbits were anesthetized and had undergone acute surgery, whereas in the present study, the rabbits
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
MEAN ARTERIAL PRESSURE (mmHg)
1164
ANG II, BARORECEPTORS, AND AVP SECRETION
Endo • 1990 Vol 127 • No 3
200 Mean Arterial Pressure 100 (mm Hg) 0
FlG. 4. Representative record showing the cardiovascular responses to bilateral carotid occlusion after vagal blockade with lidocaine.
Arterial Pressure 100 (mm Hg)
Heart Rate (bpm)
0 400 300 200
Right Atrial Pressure (cm H2O)
•
*
%
-5
were conscious and had recovered from earlier surgery. In addition, the resting values for arterial pressure, RAP, and PAVP concentration in the rabbits studied by Courneya et al. were considerably higher than those in the present study. It is also worth pointing out that Courneya et al. reported that aortic nerve section did not alter the blood pressure responses to changes in carotid sinus pressure, a finding that disagrees with the results of Yamazaki and Sagawa (9). Infusion of Ang II at 10 and 20 ng/kg-min increased arterial pressure without changing HR and increased PAVP concentration by 50 to 100%. Carotid occlusion during Ang II infusion again failed to increase PAVP concentration. Thus, it was not possible to conclude from these experiments whether there is an interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. It was, however, clear that Ang II did not alter the blood pressure or HR responses to carotid occlusion, and this agrees with a previous report by Cowley et al. (11). This suggests that Ang II does not inhibit the baroreceptor reflexes as has been suggested by others (5, 12,13). Because it is known that increases in atrial pressure can inhibit AVP secretion via vagal afferents (4), and because RAP increased in the present study, additional studies were performed after bilateral vagotomy. Vagotomy was produced either by application of lidocaine to the vagi or by surgical vagotomy. Vagotomy increased HR in all rabbits, increased arterial pressure in some, and did not change PAVP concentration. The lack of an AVP response to vagotomy is consistent with previous reports (14, 15), although others have observed small
increases in PAVP levels after vagotomy (16-18). This suggests that there is little tonic inhibition of AVP secretion arising from the heart (although such an influence may have been masked, at least in some rabbits, by the increase in arterial pressure after vagotomy). After vagotomy, carotid occlusion significantly increased PAVP concentration. This differs from the results of Courneya et al. (7), but agrees with the results of other investigators (16, 18-20). The results indicate that the carotid sinus receptors do exert a tonic inhibitory effect on AVP release and suggest that the failure of carotid occlusion to increase AVP secretion in animals with intact vagi is due to the increase in atrial pressure. Infusion of Ang II after vagotomy produced cardiovascular and AVP responses similar to those in intact rabbits. The AVP response to carotid occlusion during Ang II infusion in the vagotomized rabbits was not significantly different from that before Ang II, i.e. Ang II did not enhance the AVP response to carotid occlusion. Thus, the results indicate that there is no significant interaction between Ang II and baroreceptor reflexes in the control of AVP secretion, at least under the conditions of the present experiments. In summary, these results demonstrate that in conscious aortic nerve-sectioned rabbits, carotid occlusion increases AVP secretion, but only if vagal influences are eliminated. Infusion of Ang II increases AVP secretion in the rabbit but does not modify the cardiovascular or AVP responses to carotid occlusion. These experiments therefore do not reveal any interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion in conscious rabbits. Thus, the increase in AVP
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
200
ANG II, BARORECEPTORS, AND AVP SECRETION
1165 I
I Sham IVagotomy
140 130
I
120
MEAN ARTERIAL PRESSURE (mmHg)
100 90 BO
FIG. 5. Effects of vagotomy and sham vagotomy on MAP, HR, PAVP concentration, and on the subsequent responses to bilateral carotid occlusion (BCO) (5 min) and Ang II infusion (10 ng/kgmin). Bars indicate the mean ±SE of observations made in eight rabbits. VAGX, After the first control period, rabbits were subjected to vagotomy (hatched bars) or sham vagotomy (open bars).
350
330
310
HEART RATE (bpm)
290 270
250
PLASMA AVP CONC. (pg/ml)
Control
VAGX
BCO
Control
All
AII+BCO
TREATMENT
secretion that occurs in hypotensive and hypovolemic states may be mediated in part by the baroreflexes and in part by Ang II, but does not depend on an interaction between these two control mechanisms.
References 1. Reid IA 1985 The renin-angiotensin system and body function. Arch Intern Med 145:1475 2. Reid IA 1984 Actions of angiotensin II on the brain: mechanisms and physiologic role. Am J Physiol 246:F533 3. Ferrario CM, Ueno Y, Diz DI, Barnes KL 1986 The renin-angiotensin system: physiological actions on the central nervous system. In: Zanchetti A, Tarazi RC (eds) Handbook of Hypertension: Pathophysiology of Hypertension—Regulatory Mechanisms. Elsevier, Amsterdam, vol 8:431 4. Share L 1988 Role of vasopressin in cardiovascular regulation. Physiol Rev 68:1248
5. Guo GB, Abboud FM 1984 Angiotensin II attenuates baroreflex control of heart rate and sympathetic activity. Am J Physiol 246:H80 6. Lumbers ER, McCloskey DI, Potter EK 1979 Inhibition by angiotensin II of baroreceptor-evoked activity in cardiac vagal efferent nerves in the dog. J Physiol (Lond) 294:69 7. Courneya CA, Rankin AJ, Wilson N, Ledsome JR 1988 Carotid sinus pressure and plasma vasopressin in anesthetized rabbits. Am J Physiol 255:H1199 8. Keil LC, Severs WB 1977 Reduction in plasma vasopressin levels of dehydrated rats following acute stress. Endocrinology 100:30 9. Yamazaki T, Sagawa K 1984 Effect of thiamylal on the response to carotid occlusion and mild hemorrhage in rabbits. Am J Physiol 246:H806 10. Isaacson JS, Reid IA 1990 Importance of endogenous angiotensin II in the cardiovascular responses to sympathetic stimulation in conscious rabbits. Circ Res 66:662 11. Cowley AW, Merrill D, Osborn J, Barber BJ 1984 Influence of vasopressin and angiotensin on baroreflexes in the dog. Circ Res 54:163
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
1
110
1166
ANG II, BARORECEPTORS, AND AVP SECRETION
hemorrhage. Am J Physiol 252:H1120 16. Share L, Levy MN 1962 Cardiovascular receptors and blood titer of antidiuretic hormone. Am J Physiol 203:425 17. Bishop VS, Thames MD, Schmid PG 1984 Effects of bilateral vagal cold block on vasopressin in conscious dogs. Am J Physiol 246:R566 18. Wood CE, Keil LC, Rudolph AM 1984 Carotid arterial control of vasopressin secretion in sheep. Am J Physiol 247-.R589 19. Clark BJ, Rocha E, Silva M 1967 An afferent pathway for the selective release of vasopressin in response to carotid occlusion and haemorrhage in the cat. J Physiol 191:529 20. Usami S, Peric B, Chien S 1962 Release of antidiuretic hormone due to common carotid occlusion and its relation with vagus nerve. Proc Soc Exp Biol Med 111:189
Gregory Pincus Memorial Lecture and Award The 1990 Gregory Pincus Memorial Lecture will be given jointly by Dr. Ronald M. Evans and Dr. Keith R. Yamamoto in conjunction with the 18th New England Endocrinology Conference which will be held on Saturday, October 13, 1990 at the Worcester Foundation for Experimental Biology in Shrewsbury, Massachusetts. These scientists, who will receive the Gregory Pincus Medal and Award, will deliver lectures concerning their work on steroid hormone receptors. For further information, please contact: Chairman, Gregory Pincus Memorial Lecture Committee Worcester Foundation for Experimental Biology 222 Maple Avenue Shrewsbury, Massachusetts 01545 Telephone No. (508) 842-8921, Extension 131 FAX No. (508) 842-9632
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
12. Mace PJE, Watson RDS, Skan W, Littler WA 1985 Inhibition of the baroreceptor heart rate reflex by angiotensin II in normal man. Cardiovasc Res 19:525 13. Garner MG, Phippard AF, Fletcher PJ, Maclean JM, Duggin GG, Horvath JS, Tiller DJ 1987 Effect of angiotensin II on baroreceptor reflex control of heart rate in conscious baboons. Hypertension 10:628 14. Goetz KL, Wang BC, Hakumaki MOK, Fater DC, Geer PG, Sundet WD 1981 Cardiovascular, renal, and humoral effects of applying local anesthetic to the atria of conscious dogs. Proc Soc Exp Biol Med 167:101 15. Quail AW, Woods RL, Korner PI 1987 Cardiac and arterial baroreceptor influences in release of vasopressin and renin during
Endo • 1990 Voll27-No3
Vol. 127, No. 3 Printed in U.S.A.
FATMA HREASH, LANNY C. KEIL, LANCE CHOU, AND IAN A. REID Department of Physiology (F.H., L.C., I.A.R.), University of California, San Francisco, San Francisco, CA 94143-0444; and Ames Research Center (L.C.K.), Moffett Field, CA 94035
ABSTRACT. Experiments were performed in conscious rabbits with sectioned aortic depressor nerves to determine whether there is an interaction between angiotensin II (Ang II) and the baroreceptor reflexes in the control of arginine vasopressin (AVP) secretion. Baroreceptor reflexes were activated by a 5- or 10-min period of bilateral carotid occlusion with or without background infusion of Ang II at 10 or 20 ng/kgmin. Carotid occlusion increased mean arterial pressure, right atrial pressure, and heart rate, but did not change plasma AVP (PAVP) concentration. Infusion of Ang II at 10 ng/kgmin increased PAVP from 4.0 ± 0.9 to 6.3 ± 1.8 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion produced the same cardiovascular changes as before Ang II, but still failed to increase PAVP.
I
N ADDITION to its well-established roles in the regulation of arterial pressure, aldosterone secretion, and renal function (1), angiotensin II (Ang II) has been implicated in the control of arginine vasopressin (AVP) secretion (2, 3). Several investigators have observed that systemic administration of Ang II can increase AVP release, although there is still debate concerning the sensitivity, magnitude, and physiological significance of this effect (2, 3). There are also questions concerning the mechanism by which Ang II increases AVP release. There is evidence for a direct action on the brain that is mediated via the subfornical organ or another circumventricular organ (2, 3). However, it is also possible that Ang II can increase AVP release by interacting with baroreceptor reflex mechanisms. This proposal is based on two sets of observations. First, it is known that both the low and high pressure baroreceptors play important roles in the control of AVP secretion (4). Second, there is considerable evidence that Ang II can interact with the baroreceptor reflexes to modulate the reflex control of heart rate (HR) Received January 5, 1990. Address all correspondence and requests for reprints to: Dr. Ian A. Reid, Department of Physiology, S-762, University of California, San Francisco, California 94143. * This research was supported by NIH Grant HL-29714.
Because increased atrial pressure can inhibit AVP secretion, the experiments were repeated in acutely vagotomized rabbits. Vagotomy increased heart rate but did not change mean arterial pressure or PAVP. Carotid occlusion after vagotomy increased PAVP from 2.2 ± 0.2 to 3.3 ± 0.5 pg/ml (P < 0.05). Ang II infusion again increased PAVP but did not enhance the AVP response to carotid occlusion (2.9 ± 0.4 to 3.9 ± 0.7 pg/ml). These results provide further evidence for a role of the carotid sinus baroreceptors and vagal afferents in the control of AVP secretion and demonstrate that Ang II stimulates AVP secretion in rabbits. However, they do not reveal any interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. {Endocrinology 127: 1160-1166, 1990)
and sympathetic nerve activity such that both are maintained at higher levels for any given level of arterial pressure (3, 5, 6). The aim of the present investigation was to determine whether there is an interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. This was accomplished by investigating the effect of bilateral carotid occlusion alone, and in combination with Ang II, on plasma AVP concentration in conscious, aortic depressor-nerve sectioned rabbits. Carotid occlusion was selected as a stimulus to AVP secretion because it has been reported to increase AVP secretion in rabbits in which the aortic depressor nerves have been sectioned (7). It was reasoned that if there is an interaction between Ang II and the baroreceptor reflexes, the combination of Ang II and carotid occlusion should produce an increase in AVP secretion that is greater than the sum of the responses to the two stimuli alone.
Materials and Methods The experiments were performed on male New Zealand White rabbits weighing 2.5 to 4.0 kg (Nitabel, Haywood, CA). Standard commercial diet (Purina Rabbit Chow, St. Louis, MO) and tap water were available ad libidum. The experiments were conducted in accordance with the University of California, San Francisco Committee on Animal Research. 1160
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
Effects of Carotid Occlusion and Angiotensin II on Vasopressin Secretion in Intact and Vagotomized Conscious Rabbits*
ANG II, BARORECEPTORS, AND AVP SECRETION Surgical procedures
Experimental protocols On the day of an experiment, rabbits were brought to the laboratory and loosely restrained in a covered stainless steel cage. Pulsatile arterial pressure, mean arterial pressure (MAP), HR, and, in some rabbits, RAP were recorded continuously throughout the experiment using Cobe transducers (Cobe Laboratories, Inc., Lakewood, CO) and a cardiovascular monitor. Cardiovascular data were simultaneously recorded on a Grass Polygraph (Grass Instruments, Quincy, MA) and digitized and stored on a PDP 11/23 Plus computer (DEC, Maynard, MA). Blood samples (vol, 2.0 ml) were collected via the femoral artery catheter and replaced with an equal vol of sterile isotonic saline. The samples were placed in chilled centrifuge tubes containing 0.2 ml 0.3 M EDTA and centrifuged at 4 C, and the plasma was frozen for the subsequent measurement of plasma AVP concentration by RIA (8). Before experiments were started, the rabbits were allowed at least 30 min for blood pressure and HR to stabilize. After control measurements had been made, both carotid arteries were occluded for 5 or 10 min by inflating the vascular occluders. This was followed by a 15-min recovery period during which blood pressure and HR returned to their preocclusion values. An infusion of Ang II (Peninsula Laboratories, Belmont, CA) (10 or 20 ng/kg-min) or saline was started, and 20 min later a second bilateral carotid occlusion was performed. Blood samples were collected at the end of each protocol period. The following groups of experiments were performed.
Exp 1. With vagus nerves intact, six rabbits underwent bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min). Six others underwent bilateral carotid occlusion (5 min) and saline infusion (0.0136 ml/min). Another six rabbits underwent bilateral carotid occlusion (5 min) and Ang II infusion (20 ng/ kg-min). The last group of six rabbits underwent bilateral carotid occlusion (10 min) and Ang II infusion (10 ng/kg-min). Exp 2. Acute vagal blockade with lidocaine was performed on six rabbits. After control measurements had been made, 3 ml 2% lidocaine were applied to the perivagal region. A blood sample was collected 5 min later, and after another 5 min, the effects of bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min) were tested. Sham vagal blockade was performed on three rabbits. This protocol was identical to that for acute vagal blockade just discussed except that 0.9% saline was administered instead of lidocaine. Two rabbits underwent surgical vagotomy and, six to 8 h later, the effects of bilateral carotid occlusion (5 min) and Ang II infusion (10 ng/kg-min) were studied as described in Exp 1. Blood pressure and HR data are presented as computergenerated means. In general, data were averaged over a 2- to 10-min period. With carotid occlusion, data collected during the last 2 to 3 min of the occlusion period were averaged. All data are expressed as the mean ± SE. Statistical evaluation of the data was performed using one- or two-way analysis of variance for repeated measures and the Neuman-Keuls multiple-range test. Where appropriate, the paired t test was also used. Changes were considered to be statistically significant when P < 0.05.
Results Effects of carotid occlusion and Ang II in rabbits with intact vagi The effects of a 5-min period of bilateral carotid occlusion before and after infusion of Ang II at 10 ng/kg-min are summarized in Fig. 1. During the first carotid occlusion, MAP increased from 82.2 ± 6.4 to 133.1 ± 8.9 mm Hg (P < 0.05), and HR increased from 257 ± 11 to 300 ± 9 beats/min (bpm) (P < 0.05). Plasma AVP (PAVP) concentration did not change significantly (4.0 ± 1.0 to 3.9 ± 0.9 pg/ml). MAP and HR rapidly returned to their control values after release of the occlusion. Infusion of Ang II increased MAP from 82.7 ± 6.4 to 97.4 ± 7.4 mm Hg (P < 0.05) but did not change HR (262 ± 12 to 262 ± 13 bpm). PAVP increased from 4.0 ± 0.9 to 6.3 ± 1 . 8 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion caused a further increase in MAP to 146.4 ± 8.3 mm Hg (P < 0.05) and increased HR to 305 ± 9 bpm (P < 0.05). These changes in MAP and HR were almost identical to those produced by carotid occlusion before Ang II. Carotid occlusion during Ang II infusion did not cause any further change in PAVP (6.3 ± 1.8 to 6.1 ± 2.0 pg/ml). Infusion of the saline vehicle had no effect on MAP, HR, or PAVP, and did not alter the responses to carotid occlusion (Fig. 1).
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
The rabbits were premedicated with acepromazine maleate (Promace, Aveco Co., Fort Dodge, IA) (2 mg/kg im) and anesthetized with sodium pentobarbital (25 mg/kg iv). Under sterile conditions, a Tygon catheter (0.04 inch id) was inserted into a femoral artery for blood pressure recording and blood sampling. Two Tygon catheters (0.03 inch id) were inserted into the left jugular vein for iv infusions. In some animals, one of the jugular catheters was advanced into the right atrium for recording right atrial pressure (RAP). In all animals, both aortic depressor nerves were identified and sectioned at their junction with the vagal and superior laryngeal nerves. The carotid arteries were isolated, and an inflatable balloon vascular occluder (2 mm id, In Vivo Metric, Healdsburg, CA) was placed around each artery without interfering with blood flow. In six rabbits, another two vascular occluders with punctured balloons were placed around the carotid arteries and associated vagus nerves. These were used to produce acute, reversible vagal blockade by local application of lidocaine. The catheters and occluders were tunneled sc, exteriorized dorsally between the scapulae, and protected by a nylon jacket (Medical Arts, Los Angeles, CA). Catheters were flushed every other day with sterile isotonic saline and filled with heparinized saline. The rabbits were treated with penicillin (Penicillin G Procaine, Hanford Co., Syracuse, NY) (300,000 U/day im) for 2 days after surgery. They were allowed to recover for at least 2 days before experiments were begun. Two rabbits were subsequently anesthetized with Brevital sodium (5-10 mg/ kg iv), and both vagus nerves were sectioned in the cervical region caudal to the junction with the superior laryngeal nerves. These animals were studied 6-8 h later (see below).
1161
1162
ANG II, BARORECEPTORS, AND AVP SECRETION
Endo • 1990 Vol 127 • No 3
•
All
Saline
170 150 •
130 •
ARTERIAL PRESSURE (mmHg)
110
•
320
FIG. 1. Effects of bilateral carotid occlusion (BCO) (5 min) on MAP, HR, and PAVP concentration before and during infusion of Ang II (All) (10 ng/kg-min) or saline. Bars indicate the mean ± SE of observations made in six rabbits.
280 -
HEART RATE (bpm)
260 •
240 •
220
10.0
8.0
6.0
PLASMA AVP CONC. (pg/ml)
4.0
2.0
0.0
Control
BCO
Control
All
AII+BCO
TREATMENT
The effects of a 5-min period of carotid occlusion before and during infusion of Ang II at 20 ng/kg-min are summarized in Fig. 2. The effects of carotid occlusion before Ang II were almost identical to those shown in Fig. 1. Infusion of Ang II increased MAP from 84.5 ± 4.7 to 100.6 ± 6.4 mm Hg (P < 0.05), but did not change HR. PAVP increased from 3.1 ± 0.7 to 5.3 ± 1.0 pg/ml (P < 0.05). Carotid occlusion during Ang II infusion again increased MAP and HR, but did not change PAVP. The effects of a 10-min period of carotid occlusion and infusion of Ang II at 10 ng/kg-min on MAP, HR, and RAP are shown in Fig. 3. Carotid occlusion caused increases in MAP and HR similar to those shown in Figs. 1 and 2, and increased RAP from -0.8 ± 1.2 to 1.7 ± 1.5 cm H2O (P < 0.05). Ang II increased MAP and PAVP (3.0 ± 0.3 to 3.5 ± 0.4 pg/ml, P < 0.05) but did not change HR or RAP. The hemodynamic responses to
carotid occlusion during Ang II infusion were similar to those before Ang II, and again PAVP did not change. Effects of uagotomy
A representative record showing the cardiovascular responses to bilateral carotid occlusion after vagal blockade with lidocaine is shown in Fig. 4. The effects of vagal blockade with lidocaine (n = 6) and surgical vagotomy (n = 2) were similar, and the data were combined into one group for analysis (Fig. 5). After vagotomy, HR increased from 272 ± 6 to 310 ± 14 bpm (P < 0.05). MAP tended to increase but not significantly (80.9 ± 2.1 to 88.7 ± 4.6 mm Hg). PAVP did not change significantly (1.9 ± 0.2 to 2.2 ± 0.2 pg/ml). Carotid occlusion after vagotomy increased MAP from 88.7 ± 4.6 to 120.3 ± 3.7 mm Hg (P < 0.05). There were small increases in HR in
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
MEAN
ANG II, BARORECEPTORS, AND AVP SECRETION
1163
120
MEAN ARTERIAL PRESSURE (mmHg)
100 •
320
100
80
320 r
r
300
HEART RATE (bpm)
HEART RATE (bpm)
280
260 •
260
PLASMA AVP CONC. (pg/ml)
RIGHT ATRIAL PRESSURE (cmH20)
Control
All
TREATMENT
FIG. 2. Effects of bilateral carotid occlusion (BCO) (5 min) on MAP, HR, and PAVP concentration before and during infusion of Ang II (All) at 20 ng/kgmin. Bars indicate the mean ±SE of observations made in six rabbits.
all animals; the overall change was from 310 ± 14 to 330 ± 16 bpm (P < 0.05). RAP increased from -1.3 ± 0.7 to 4.5 ± 0.7 cm H2O (P < 0.05). PAVP increased from 2.2 ± 0.2 to 3.3 ± 0.5 pg/ml (P < 0.05). Infusion of Ang II increased MAP and PAVP without changing HR or RAP. Carotid occlusion during Ang II infusion produced increases in MAP, HR, RAP, and PAVP that were not significantly different from those before Ang II. Sham vagotomy had no effect on any of the measured variables and did not alter the cardiovascular or AVP responses to carotid occlusion and Ang II (Fig. 5).
Discussion Bilateral carotid occlusion is a convenient and effective method of activating baroreceptor reflexes, particularly when the buffering effect of the aortic arch baroreceptors
-2
Control
BCO
Control
All
AII+BCO
TREATMENT
FIG. 3. Effects of bilateral carotid occlusion (BCO) (10 min) on MAP, HR, and RAP before and during infusion of Ang II (All) at 10 ng/kgmin. Bars indicate the mean ±SE of observations made in six rabbits.
is eliminated by sectioning the aortic depressor nerves (9, 10). In the present study, carotid occlusion produced marked increases in arterial pressure and HR similar to those observed in other studies (9, 10). On the other hand, carotid occlusion failed to increase PAVP concentration. The same result was obtained whether the period of carotid occlusion was 5 or 10 min. The failure of carotid occlusion to increase PAVP concentration was unexpected in view of the report by Courneya et al. (7) that reduced carotid sinus pressure increased PAVP concentration in aortic depressor nerve sectioned rabbits. The reason for the difference between the present results and those of Courneya et al. is not clear but is probably related to differences in experimental design. For example, in the study by Courneya et al. (7), the rabbits were anesthetized and had undergone acute surgery, whereas in the present study, the rabbits
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
MEAN ARTERIAL PRESSURE (mmHg)
1164
ANG II, BARORECEPTORS, AND AVP SECRETION
Endo • 1990 Vol 127 • No 3
200 Mean Arterial Pressure 100 (mm Hg) 0
FlG. 4. Representative record showing the cardiovascular responses to bilateral carotid occlusion after vagal blockade with lidocaine.
Arterial Pressure 100 (mm Hg)
Heart Rate (bpm)
0 400 300 200
Right Atrial Pressure (cm H2O)
•
*
%
-5
were conscious and had recovered from earlier surgery. In addition, the resting values for arterial pressure, RAP, and PAVP concentration in the rabbits studied by Courneya et al. were considerably higher than those in the present study. It is also worth pointing out that Courneya et al. reported that aortic nerve section did not alter the blood pressure responses to changes in carotid sinus pressure, a finding that disagrees with the results of Yamazaki and Sagawa (9). Infusion of Ang II at 10 and 20 ng/kg-min increased arterial pressure without changing HR and increased PAVP concentration by 50 to 100%. Carotid occlusion during Ang II infusion again failed to increase PAVP concentration. Thus, it was not possible to conclude from these experiments whether there is an interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion. It was, however, clear that Ang II did not alter the blood pressure or HR responses to carotid occlusion, and this agrees with a previous report by Cowley et al. (11). This suggests that Ang II does not inhibit the baroreceptor reflexes as has been suggested by others (5, 12,13). Because it is known that increases in atrial pressure can inhibit AVP secretion via vagal afferents (4), and because RAP increased in the present study, additional studies were performed after bilateral vagotomy. Vagotomy was produced either by application of lidocaine to the vagi or by surgical vagotomy. Vagotomy increased HR in all rabbits, increased arterial pressure in some, and did not change PAVP concentration. The lack of an AVP response to vagotomy is consistent with previous reports (14, 15), although others have observed small
increases in PAVP levels after vagotomy (16-18). This suggests that there is little tonic inhibition of AVP secretion arising from the heart (although such an influence may have been masked, at least in some rabbits, by the increase in arterial pressure after vagotomy). After vagotomy, carotid occlusion significantly increased PAVP concentration. This differs from the results of Courneya et al. (7), but agrees with the results of other investigators (16, 18-20). The results indicate that the carotid sinus receptors do exert a tonic inhibitory effect on AVP release and suggest that the failure of carotid occlusion to increase AVP secretion in animals with intact vagi is due to the increase in atrial pressure. Infusion of Ang II after vagotomy produced cardiovascular and AVP responses similar to those in intact rabbits. The AVP response to carotid occlusion during Ang II infusion in the vagotomized rabbits was not significantly different from that before Ang II, i.e. Ang II did not enhance the AVP response to carotid occlusion. Thus, the results indicate that there is no significant interaction between Ang II and baroreceptor reflexes in the control of AVP secretion, at least under the conditions of the present experiments. In summary, these results demonstrate that in conscious aortic nerve-sectioned rabbits, carotid occlusion increases AVP secretion, but only if vagal influences are eliminated. Infusion of Ang II increases AVP secretion in the rabbit but does not modify the cardiovascular or AVP responses to carotid occlusion. These experiments therefore do not reveal any interaction between Ang II and the baroreceptor reflexes in the control of AVP secretion in conscious rabbits. Thus, the increase in AVP
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
200
ANG II, BARORECEPTORS, AND AVP SECRETION
1165 I
I Sham IVagotomy
140 130
I
120
MEAN ARTERIAL PRESSURE (mmHg)
100 90 BO
FIG. 5. Effects of vagotomy and sham vagotomy on MAP, HR, PAVP concentration, and on the subsequent responses to bilateral carotid occlusion (BCO) (5 min) and Ang II infusion (10 ng/kgmin). Bars indicate the mean ±SE of observations made in eight rabbits. VAGX, After the first control period, rabbits were subjected to vagotomy (hatched bars) or sham vagotomy (open bars).
350
330
310
HEART RATE (bpm)
290 270
250
PLASMA AVP CONC. (pg/ml)
Control
VAGX
BCO
Control
All
AII+BCO
TREATMENT
secretion that occurs in hypotensive and hypovolemic states may be mediated in part by the baroreflexes and in part by Ang II, but does not depend on an interaction between these two control mechanisms.
References 1. Reid IA 1985 The renin-angiotensin system and body function. Arch Intern Med 145:1475 2. Reid IA 1984 Actions of angiotensin II on the brain: mechanisms and physiologic role. Am J Physiol 246:F533 3. Ferrario CM, Ueno Y, Diz DI, Barnes KL 1986 The renin-angiotensin system: physiological actions on the central nervous system. In: Zanchetti A, Tarazi RC (eds) Handbook of Hypertension: Pathophysiology of Hypertension—Regulatory Mechanisms. Elsevier, Amsterdam, vol 8:431 4. Share L 1988 Role of vasopressin in cardiovascular regulation. Physiol Rev 68:1248
5. Guo GB, Abboud FM 1984 Angiotensin II attenuates baroreflex control of heart rate and sympathetic activity. Am J Physiol 246:H80 6. Lumbers ER, McCloskey DI, Potter EK 1979 Inhibition by angiotensin II of baroreceptor-evoked activity in cardiac vagal efferent nerves in the dog. J Physiol (Lond) 294:69 7. Courneya CA, Rankin AJ, Wilson N, Ledsome JR 1988 Carotid sinus pressure and plasma vasopressin in anesthetized rabbits. Am J Physiol 255:H1199 8. Keil LC, Severs WB 1977 Reduction in plasma vasopressin levels of dehydrated rats following acute stress. Endocrinology 100:30 9. Yamazaki T, Sagawa K 1984 Effect of thiamylal on the response to carotid occlusion and mild hemorrhage in rabbits. Am J Physiol 246:H806 10. Isaacson JS, Reid IA 1990 Importance of endogenous angiotensin II in the cardiovascular responses to sympathetic stimulation in conscious rabbits. Circ Res 66:662 11. Cowley AW, Merrill D, Osborn J, Barber BJ 1984 Influence of vasopressin and angiotensin on baroreflexes in the dog. Circ Res 54:163
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
1
110
1166
ANG II, BARORECEPTORS, AND AVP SECRETION
hemorrhage. Am J Physiol 252:H1120 16. Share L, Levy MN 1962 Cardiovascular receptors and blood titer of antidiuretic hormone. Am J Physiol 203:425 17. Bishop VS, Thames MD, Schmid PG 1984 Effects of bilateral vagal cold block on vasopressin in conscious dogs. Am J Physiol 246:R566 18. Wood CE, Keil LC, Rudolph AM 1984 Carotid arterial control of vasopressin secretion in sheep. Am J Physiol 247-.R589 19. Clark BJ, Rocha E, Silva M 1967 An afferent pathway for the selective release of vasopressin in response to carotid occlusion and haemorrhage in the cat. J Physiol 191:529 20. Usami S, Peric B, Chien S 1962 Release of antidiuretic hormone due to common carotid occlusion and its relation with vagus nerve. Proc Soc Exp Biol Med 111:189
Gregory Pincus Memorial Lecture and Award The 1990 Gregory Pincus Memorial Lecture will be given jointly by Dr. Ronald M. Evans and Dr. Keith R. Yamamoto in conjunction with the 18th New England Endocrinology Conference which will be held on Saturday, October 13, 1990 at the Worcester Foundation for Experimental Biology in Shrewsbury, Massachusetts. These scientists, who will receive the Gregory Pincus Medal and Award, will deliver lectures concerning their work on steroid hormone receptors. For further information, please contact: Chairman, Gregory Pincus Memorial Lecture Committee Worcester Foundation for Experimental Biology 222 Maple Avenue Shrewsbury, Massachusetts 01545 Telephone No. (508) 842-8921, Extension 131 FAX No. (508) 842-9632
Downloaded from https://academic.oup.com/endo/article-abstract/127/3/1160/2533809 by University of Newcastle user on 18 January 2019
12. Mace PJE, Watson RDS, Skan W, Littler WA 1985 Inhibition of the baroreceptor heart rate reflex by angiotensin II in normal man. Cardiovasc Res 19:525 13. Garner MG, Phippard AF, Fletcher PJ, Maclean JM, Duggin GG, Horvath JS, Tiller DJ 1987 Effect of angiotensin II on baroreceptor reflex control of heart rate in conscious baboons. Hypertension 10:628 14. Goetz KL, Wang BC, Hakumaki MOK, Fater DC, Geer PG, Sundet WD 1981 Cardiovascular, renal, and humoral effects of applying local anesthetic to the atria of conscious dogs. Proc Soc Exp Biol Med 167:101 15. Quail AW, Woods RL, Korner PI 1987 Cardiac and arterial baroreceptor influences in release of vasopressin and renin during
Endo • 1990 Voll27-No3
