Endothelium-derived relaxing factor regulates renin release in vivo DAVID
H. SIGMON,
Hypertension
OSCAR A. CARRETERO,
and Vascular
Research
Division,
Sigmon, David H., Oscar A. Carretero, and William H. Beierwaltes. Endothelium-derived relaxing factor 263 regulates renin release in vivo. Am. J. Physiol. F256-F261, (Renal Fluid Electrolyte Physiol. 32): 1992.-Endothelium-derived relaxing factor (EDRF), through its inhibitory second messenger guanosine 3’,5’-cyclic monophosphate (cGMP), inhibits renin release in vitro. To determine whether EDRF affects renin in vivo, we tested whether EDRF synthesis inhibition could stimulate renin secretion in intact rats. Because EDRF synthesis inhibition increases blood pressure and consequently withdraws sympathetic activity (both renin inhibitory signals), we also studied the effect of L-N”-nitroarginine methyl ester (L-NAME) when renal perfusion pressure was controlled and during ,8-adrenergic blockade. Mean blood pressure (BP), heart rate (HR), and plasma renin activity (PRA) were measured in anesthetized rats before and after EDRF synthesis inhibition by a 10 mg/kg body wt bolus of L-NAME. L-NAME decreased PRA by 67% [from 11.0 t 2.7 to 3.7 t 0.8 ng angiotensin I (ANG I) *ml-l h-l, n = 12; P < O.OOl], increased BP by 20 k 2 mmHg (P < O.OOl), and decreased HR from 332 t 8 to 312 t 9 beats/min (P < 0.005). We repeated our experiment in rats instrumented with an intraaortic balloon catheter to control renal perfusion pressure and pretreated with propranolol to eliminate the ,8-adrenergic effect. Under these conditions, L-NAME now increased PRA by 55% (from 6.9 & 1.9 to 10.8 t 2.6 ng ANG Iml-l h-l, n = 12; P < 0.02), whereas renal perfusion pressure was unchanged (91 ~fr4 vs. 90 t 4 mmHg). HR increased slightly from 308 t 5 to 315 t 3 beats/min (P < 0.005). These results suggest that, when changes in renal perfusion pressure and ,0-adrenergic activity are controlled, EDRF synthesis inhibition with L-NAME results in an increase in PRA. Therefore tonic release of EDRF from the renal endothelium, presumably through the inhibitory second messenger cGMP, may serve as an inhibitory modulator of renin release in the whole animal. plasma renin activity; endothelium; nitric oxide; nitroarginine; ,&adrenergic; tubuloglomerular feedback l
l
ENDOTHELIUM IS A RICH SOURCE of vasoactive faCtors, in particular the endothelium-derived relaxing factor (EDRF), which has been suggested to be nitric oxide (1, 20) or possibly a nitrosothiol (18). EDRF is derived from an L-arginine substrate and acts through activation of soluble guanylate cyclase (1, 17, 21) and subsequently by the fact that guanosine 3’,5’-cyclic monophosphate (cGMP) is the second messenger in endothelium-dependent relaxation (17). Recent investigation has focused on the possible role of EDRF as a regulator of organ as well as vascular function. In the kidney, Baylis et al. (3) have demonstrated that EDRF inhibition results in increased renal vascular resistance with decreased renal plasma flow and glomerular filtration rate. This suggests that tonic release of EDRF is involved in maintaining renal perfusion and function. Several in vitro studies have suggested that the renal vascular endothelium may directly modulate renin release. From use of renal cortical slices, it has been shown that EDRF release from the endothelium of the
THE
F256
0363-6127/92
$2.00
Copyright
AND WILLIAM Henry
Ford Hospital,
H. BEIERWALTES Detroit,
Michigan
48202
dog (26) or rat renal blood vessels (4) inhibits renin release. Inhibition of EDRF with an antagonist of its L-arginine substrate, NG-monomethyl-L-arginine (LNMMA), stimulates basal release (5). Additionally, renal cGMP, elicited by atria1 natriuretic peptide, has been shown to inhibit both basal (15) and stimulated (12) renin release. Thus it may be that EDRF-mediated renin inhibition may be due to a direct effect of cGMP as an inhibitory second messenger. Despite these observations, it is not known whether there is a significant role for EDRF-mediated inhibition of renin release in vivo. Therefore, this study was undertaken to extend the in vitro observations to the whole animal and, in particular, to determine whether EDRF has a tonic inhibitory influence on renin release in vivo. By inhibiting EDRF synthesis using L-N”-nitroarginine methyl ester (L-NAME, an L-arginine analogue which acts as a substrate antagonist), we would remove its effect on the renal juxtaglomerular cells. We hypothesized that in this condition we should see an increase in plasma renin activity (PRA). However, because there are a number of other adaptive or regulatory mechanisms in vivo that influence renin secretion, such as the renal baroreceptor, ,&adrenergic activity, and tubuloglomerular feedback (TGF), our protocols were extended to try and exclude each of these factors in order to unmask the hypothesized direct inhibitory influence of EDRF. METHODS
All studies were performed with male Sprague-Dawley rats weighing 250-350 g, fasted overnight, but allowed free access to water. These were anesthetized by an intraperitoneal injection of 125 mg/kg body wt thiobutabarbital (Inactin, Andrew Lockwood) and placed on a heating pad to maintain normal body temperature. The rats were surgically prepared by first inserting a tracheal tube using polyethylene tubing (PE-260, Fisher Scientific) for spontaneous breathing of room air, and a femoral artery catheter (using PE-50 tubing) was used together with a Statham pressure transducer and brush recorder to monitor blood pressure. Finally, the rats were instrumented with a femoral vein catheter (using PE-50 tubing) that was used for infusions and blood sampling. Each rat received a supplement of 2 ml plasma (24-h nephrectomized donor rat) at a rate of 50 pl/min following surgery to minimize any changes in hematocrit and plasma protein according to the technique of Arendshorst (2). After this supplement, rats were maintained on a constant infusion of 50 pl/min saline throughout the duration of the experiment. To inhibit endogenous EDRF production, we used L-NAME (Sigma Chemical) (19). We have previously reported that a 10 mg/kg body wt bolus dose of L-NAME resulted in a prolonged and maximal systemic pressor response as well as complete inhibition of endothelium-dependent renal vasodilation (6). This dose was used in all the following experimental protocols to inhibit EDRF synthesis. Protocol 1: effect of L-NAME on PRA, blood pressure, and heart rate. Our first experimental protocol made use of 24 rats.
0 1992 the American
Physiological
Society
Downloaded from www.physiology.org/journal/ajprenal by ${individualUser.givenNames} ${individualUser.surname} (132.210.236.020) on January 11, 2019.
ENDOTHELIUM
AND
PLASMA
Blood pressure was monitored throughout the experiment. After surgical preparation, the rats were allowed to stabilize for 40 min. After this recovery period, we measured the resting heart rate and sampled 0.5 ml of blood for baseline PRA (control period). The volume of sampled blood was replaced with 0.5 ml of 24-h nephrectomized donor blood. Blood samples were collected in a l-ml syringe containing 50 ~1 of 3.8% EDTA and kept on ice until centrifugation. Five minutes after blood was sampled, when blood pressure was again stable, either a 0.2-ml bolus of saline vehicle (n = 12) or 10 mg/kg body wt of L-NAME (n = 12) was injected into the rat through the femoral vein. Fifteen minutes after the L-NAME was given, when the pressor effect was maximal, heart rate was again recorded and blood was sampled (treatment period). The sampled blood volume was again replaced. After an additional 5 min, a 300 mg/kg bolus of the EDRF substrate, L-arginine (Sigma), was given to the LNAME-treated rats. After an additional 15 min, blood pressure, heart rate, and PRA were again recorded. Hematocrit was measured before and after the control and treatment periods to ensure that the cell/plasma ratio remained stable. Protocol 2: effect of L-NAME on PRA, blood pressure, and
RENIN
F257
ACTIVITY
mg/kg bolus of L-arginine, waited 15 min, and then determined blood pressure, heart rate, and PRA. Protocol 4: effect of L-NAME on PRA, blood pressure, and heart rate with p-adrenergic blockade, inhibition of TGF, and constant renal perfusionpressure.Inhibitors of EDRF synthesis have been shown to decrease renal blood flow and glomerular filtration rate (3,27), resulting in a decreased delivery of sodium chloride to the macula densa, which may stimulate renin release through TGF (7,13). An additional set of experiments, using 20 rats, was run to control this variable. In these rats we tied off the ureters for a period of 1 h; a procedure that has been shown by micropuncture studies to abolish TGF (9). Thirty minutes after occluding the ureters we injected a bolus of 1 mg/kg body wt of the P-adrenergic blocker propranolol (Ayerst) followed by a supplemental infusion of 0.3 mg kg body wt-l h-l for the duration of the experiment (22) as before. The time course for these experiments was the same as described above. In this series of experiments two different groups of rats were studied. The first group of rats (n = 10) served as a time control and received neither an intra-aortic balloon catheter nor L-NAME. In the second group (n = lo), rats were instrumented with an intrainjection, the balloon heart rate while maintaining renal perfusion pressureconstant. aortic balloon catheter. After L-NAME catheter was inflated to maintain constant renal perfusion presBecause increased renal perfusion pressure inhibits renin secresure. Fifteen minutes after a constant renal perfusion pressure tion (24) and L-NAME increased blood pressure, additional was achieved, heart rate was recorded and blood was sampled experiments were carried out in 12 rats according to the same (treatment period). protocol as above, except that these were instrumented with an PRA was measured by radioimmunoassay of the generation intra-aortic balloon catheter by which we could maintain a conof angiotensin I (ANG I) using a modification of the technique stant renal perfusion pressure. The balloon catheter consisted of of Haber et al. (11) as described previously (8). Results are a 0.5-mm length of Silastic tubing (0.012 in. ID, 0.025 in. OD) expressed as nanograms ANG I per milliliter per hour. attached to the tip of a PE-10 polyethylene catheter (15-20 cm Our results are means * SE obtained in each group of experlong) by means of a cyanoacrylic adhesive (Loctite) and secured imental animals. Changes in experimental parameters within with 6-O silk suture. The tip of the Silastic tubing was sealed the same group were analyzed by Student’s paired t test, with Silastic silicone medical adhesive (Dow Corning). The balwhereas differences between groups were analyzed using Stuloon catheter was inserted into the left carotid artery and fed to dent’s unpaired t test. a position in the aorta just superior to the origin of the right renal artery. Proper placement was always confirmed at the RESULTS conclusion of the experiment. The catheter could be inflated to Effect of L-NAME on PRA, blood pressure, and heart partially obstruct the aorta by means of a loo-p1 Hamilton rate with and without constant renal perfusion pressure. syringe filled with saline. The protocol for these experiments Table 1 shows the response of PRA, blood pressure, and was the same as above, except that following L-NAME adminheart rate to either vehicle or L-NAME with and without istration the balloon catheter was inflated to maintain renal perfusion pressure constant at control (pre+NAME) levels as constant renal perfusion pressure. The vehicle had no monitored via the femoral artery catheter. effect on either heart rate or blood pressure, but it did Protocol 3: effect of L-NAME on PRA, blood pressure, and result in a small but significant decrease in PRA (27 t heart rate with ,&adrenergic blockade and constant renal perfu9%, P < 0.05). A bolus injection of L-NAME increased sion pressure. The ability of inhibitors of EDRF synthesis to blood pressure by 20 t 7 mmHg, decreased heart rate by increase blood pressure and decrease heart rate (23) suggests 24 t 6 beats/min, and resulted in a 68.5 t 3.3% decrease sympathetic activity withdrawal, which could decrease renin in PRA (P < O.OOl), to a level of one-half that seen in the release. An additional set of experiments, using 36 rats, was run vehicle controls (Fig. 1). Not shown in Table 1, the reto control this variable. In these rats we injected a bolus of 1 sponse to a bolus of L-arginine resulted in blood pressure mg/kg body wt of the ,8-adrenergic blocker propranolol (Ayerst) returning to normal (107 t 3 mmHg), heart rate increasfollowed by a supplemental infusion of 0.3 mg kg body ing to 363 t 9 beats/min, and a slight but insignificant wt-l.h-’ for the duration of the experiment (22). The time increase in PRA to 4.6 t 1.7 ng ANG I ml-l 9h-l. Hecourse for these experiments was the same as described above. In this series of experiments three different groups of rats, all matocrit was unchanged and did not differ between the treated with propranolol, were studied. The first group of rats (n control and experimental groups. = 12) served as a time control and received neither an intraWhen renal perfusion pressure was maintained conaortic balloon catheter nor L-NAME. The second group of rats stant at control levels (Table l), L-NAME still resulted in (n = 12) received a bolus of L-NAME, and the change in blood a decreased heart rate as before (20 t 5 beats/min). When pressure was monitored. In the third group (n = 12), rats were renal perfusion pressure was maintained, L-NAME treatinstrumented with an intra-aortic balloon catheter. After Lment did not change PRA significantly (Fig. 1). NAME injection, the balloon catheter was inflated to maintain Effect of L-NAME on PRA, blood pressure, and heart constant renal perfusion pressure. Fifteen minutes after a conrate in propranolol- treated animals with and without constant renal perfusion pressure was achieved, heart rate was retrolling renal perfusion pressure. As shown in Table 2, corded and blood was sampled (treatment period). In the third ,&adrenergic blockade with propranolol resulted in a 21 t group with both P-blockade and constant renal perfusion pres2 mmHg decrease in blood pressure (P c 0.001) and a 38 sure after L-NAME, we concluded the protocol by giving the 300 l
l
l
l
Downloaded from www.physiology.org/journal/ajprenal by ${individualUser.givenNames} ${individualUser.surname} (132.210.236.020) on January 11, 2019.
F258
ENDOTHELIUM
AND
PLASMA
Table 1. PRA, RPP, and heart rate before and after L-NAME RPP,
RENIN
treatment
12
in presence
or absence of constant
Heart Rate, beats/min
mmHg
n
Vehicle
ACTIVITY
ng ANG
Control
Treated
Control
Treated
Control
102tl
101&l
335t5
33lt8
10.2t3.3
P
PRA, 1. ml-l
RPP
- h-l Treated
7.3t2.3 co.05
L-NAME
12
99&l
119&2
P
332t8
H. SIGMON,
Hypertension
OSCAR A. CARRETERO,
and Vascular
Research
Division,
Sigmon, David H., Oscar A. Carretero, and William H. Beierwaltes. Endothelium-derived relaxing factor 263 regulates renin release in vivo. Am. J. Physiol. F256-F261, (Renal Fluid Electrolyte Physiol. 32): 1992.-Endothelium-derived relaxing factor (EDRF), through its inhibitory second messenger guanosine 3’,5’-cyclic monophosphate (cGMP), inhibits renin release in vitro. To determine whether EDRF affects renin in vivo, we tested whether EDRF synthesis inhibition could stimulate renin secretion in intact rats. Because EDRF synthesis inhibition increases blood pressure and consequently withdraws sympathetic activity (both renin inhibitory signals), we also studied the effect of L-N”-nitroarginine methyl ester (L-NAME) when renal perfusion pressure was controlled and during ,8-adrenergic blockade. Mean blood pressure (BP), heart rate (HR), and plasma renin activity (PRA) were measured in anesthetized rats before and after EDRF synthesis inhibition by a 10 mg/kg body wt bolus of L-NAME. L-NAME decreased PRA by 67% [from 11.0 t 2.7 to 3.7 t 0.8 ng angiotensin I (ANG I) *ml-l h-l, n = 12; P < O.OOl], increased BP by 20 k 2 mmHg (P < O.OOl), and decreased HR from 332 t 8 to 312 t 9 beats/min (P < 0.005). We repeated our experiment in rats instrumented with an intraaortic balloon catheter to control renal perfusion pressure and pretreated with propranolol to eliminate the ,8-adrenergic effect. Under these conditions, L-NAME now increased PRA by 55% (from 6.9 & 1.9 to 10.8 t 2.6 ng ANG Iml-l h-l, n = 12; P < 0.02), whereas renal perfusion pressure was unchanged (91 ~fr4 vs. 90 t 4 mmHg). HR increased slightly from 308 t 5 to 315 t 3 beats/min (P < 0.005). These results suggest that, when changes in renal perfusion pressure and ,0-adrenergic activity are controlled, EDRF synthesis inhibition with L-NAME results in an increase in PRA. Therefore tonic release of EDRF from the renal endothelium, presumably through the inhibitory second messenger cGMP, may serve as an inhibitory modulator of renin release in the whole animal. plasma renin activity; endothelium; nitric oxide; nitroarginine; ,&adrenergic; tubuloglomerular feedback l
l
ENDOTHELIUM IS A RICH SOURCE of vasoactive faCtors, in particular the endothelium-derived relaxing factor (EDRF), which has been suggested to be nitric oxide (1, 20) or possibly a nitrosothiol (18). EDRF is derived from an L-arginine substrate and acts through activation of soluble guanylate cyclase (1, 17, 21) and subsequently by the fact that guanosine 3’,5’-cyclic monophosphate (cGMP) is the second messenger in endothelium-dependent relaxation (17). Recent investigation has focused on the possible role of EDRF as a regulator of organ as well as vascular function. In the kidney, Baylis et al. (3) have demonstrated that EDRF inhibition results in increased renal vascular resistance with decreased renal plasma flow and glomerular filtration rate. This suggests that tonic release of EDRF is involved in maintaining renal perfusion and function. Several in vitro studies have suggested that the renal vascular endothelium may directly modulate renin release. From use of renal cortical slices, it has been shown that EDRF release from the endothelium of the
THE
F256
0363-6127/92
$2.00
Copyright
AND WILLIAM Henry
Ford Hospital,
H. BEIERWALTES Detroit,
Michigan
48202
dog (26) or rat renal blood vessels (4) inhibits renin release. Inhibition of EDRF with an antagonist of its L-arginine substrate, NG-monomethyl-L-arginine (LNMMA), stimulates basal release (5). Additionally, renal cGMP, elicited by atria1 natriuretic peptide, has been shown to inhibit both basal (15) and stimulated (12) renin release. Thus it may be that EDRF-mediated renin inhibition may be due to a direct effect of cGMP as an inhibitory second messenger. Despite these observations, it is not known whether there is a significant role for EDRF-mediated inhibition of renin release in vivo. Therefore, this study was undertaken to extend the in vitro observations to the whole animal and, in particular, to determine whether EDRF has a tonic inhibitory influence on renin release in vivo. By inhibiting EDRF synthesis using L-N”-nitroarginine methyl ester (L-NAME, an L-arginine analogue which acts as a substrate antagonist), we would remove its effect on the renal juxtaglomerular cells. We hypothesized that in this condition we should see an increase in plasma renin activity (PRA). However, because there are a number of other adaptive or regulatory mechanisms in vivo that influence renin secretion, such as the renal baroreceptor, ,&adrenergic activity, and tubuloglomerular feedback (TGF), our protocols were extended to try and exclude each of these factors in order to unmask the hypothesized direct inhibitory influence of EDRF. METHODS
All studies were performed with male Sprague-Dawley rats weighing 250-350 g, fasted overnight, but allowed free access to water. These were anesthetized by an intraperitoneal injection of 125 mg/kg body wt thiobutabarbital (Inactin, Andrew Lockwood) and placed on a heating pad to maintain normal body temperature. The rats were surgically prepared by first inserting a tracheal tube using polyethylene tubing (PE-260, Fisher Scientific) for spontaneous breathing of room air, and a femoral artery catheter (using PE-50 tubing) was used together with a Statham pressure transducer and brush recorder to monitor blood pressure. Finally, the rats were instrumented with a femoral vein catheter (using PE-50 tubing) that was used for infusions and blood sampling. Each rat received a supplement of 2 ml plasma (24-h nephrectomized donor rat) at a rate of 50 pl/min following surgery to minimize any changes in hematocrit and plasma protein according to the technique of Arendshorst (2). After this supplement, rats were maintained on a constant infusion of 50 pl/min saline throughout the duration of the experiment. To inhibit endogenous EDRF production, we used L-NAME (Sigma Chemical) (19). We have previously reported that a 10 mg/kg body wt bolus dose of L-NAME resulted in a prolonged and maximal systemic pressor response as well as complete inhibition of endothelium-dependent renal vasodilation (6). This dose was used in all the following experimental protocols to inhibit EDRF synthesis. Protocol 1: effect of L-NAME on PRA, blood pressure, and heart rate. Our first experimental protocol made use of 24 rats.
0 1992 the American
Physiological
Society
Downloaded from www.physiology.org/journal/ajprenal by ${individualUser.givenNames} ${individualUser.surname} (132.210.236.020) on January 11, 2019.
ENDOTHELIUM
AND
PLASMA
Blood pressure was monitored throughout the experiment. After surgical preparation, the rats were allowed to stabilize for 40 min. After this recovery period, we measured the resting heart rate and sampled 0.5 ml of blood for baseline PRA (control period). The volume of sampled blood was replaced with 0.5 ml of 24-h nephrectomized donor blood. Blood samples were collected in a l-ml syringe containing 50 ~1 of 3.8% EDTA and kept on ice until centrifugation. Five minutes after blood was sampled, when blood pressure was again stable, either a 0.2-ml bolus of saline vehicle (n = 12) or 10 mg/kg body wt of L-NAME (n = 12) was injected into the rat through the femoral vein. Fifteen minutes after the L-NAME was given, when the pressor effect was maximal, heart rate was again recorded and blood was sampled (treatment period). The sampled blood volume was again replaced. After an additional 5 min, a 300 mg/kg bolus of the EDRF substrate, L-arginine (Sigma), was given to the LNAME-treated rats. After an additional 15 min, blood pressure, heart rate, and PRA were again recorded. Hematocrit was measured before and after the control and treatment periods to ensure that the cell/plasma ratio remained stable. Protocol 2: effect of L-NAME on PRA, blood pressure, and
RENIN
F257
ACTIVITY
mg/kg bolus of L-arginine, waited 15 min, and then determined blood pressure, heart rate, and PRA. Protocol 4: effect of L-NAME on PRA, blood pressure, and heart rate with p-adrenergic blockade, inhibition of TGF, and constant renal perfusionpressure.Inhibitors of EDRF synthesis have been shown to decrease renal blood flow and glomerular filtration rate (3,27), resulting in a decreased delivery of sodium chloride to the macula densa, which may stimulate renin release through TGF (7,13). An additional set of experiments, using 20 rats, was run to control this variable. In these rats we tied off the ureters for a period of 1 h; a procedure that has been shown by micropuncture studies to abolish TGF (9). Thirty minutes after occluding the ureters we injected a bolus of 1 mg/kg body wt of the P-adrenergic blocker propranolol (Ayerst) followed by a supplemental infusion of 0.3 mg kg body wt-l h-l for the duration of the experiment (22) as before. The time course for these experiments was the same as described above. In this series of experiments two different groups of rats were studied. The first group of rats (n = 10) served as a time control and received neither an intra-aortic balloon catheter nor L-NAME. In the second group (n = lo), rats were instrumented with an intrainjection, the balloon heart rate while maintaining renal perfusion pressureconstant. aortic balloon catheter. After L-NAME catheter was inflated to maintain constant renal perfusion presBecause increased renal perfusion pressure inhibits renin secresure. Fifteen minutes after a constant renal perfusion pressure tion (24) and L-NAME increased blood pressure, additional was achieved, heart rate was recorded and blood was sampled experiments were carried out in 12 rats according to the same (treatment period). protocol as above, except that these were instrumented with an PRA was measured by radioimmunoassay of the generation intra-aortic balloon catheter by which we could maintain a conof angiotensin I (ANG I) using a modification of the technique stant renal perfusion pressure. The balloon catheter consisted of of Haber et al. (11) as described previously (8). Results are a 0.5-mm length of Silastic tubing (0.012 in. ID, 0.025 in. OD) expressed as nanograms ANG I per milliliter per hour. attached to the tip of a PE-10 polyethylene catheter (15-20 cm Our results are means * SE obtained in each group of experlong) by means of a cyanoacrylic adhesive (Loctite) and secured imental animals. Changes in experimental parameters within with 6-O silk suture. The tip of the Silastic tubing was sealed the same group were analyzed by Student’s paired t test, with Silastic silicone medical adhesive (Dow Corning). The balwhereas differences between groups were analyzed using Stuloon catheter was inserted into the left carotid artery and fed to dent’s unpaired t test. a position in the aorta just superior to the origin of the right renal artery. Proper placement was always confirmed at the RESULTS conclusion of the experiment. The catheter could be inflated to Effect of L-NAME on PRA, blood pressure, and heart partially obstruct the aorta by means of a loo-p1 Hamilton rate with and without constant renal perfusion pressure. syringe filled with saline. The protocol for these experiments Table 1 shows the response of PRA, blood pressure, and was the same as above, except that following L-NAME adminheart rate to either vehicle or L-NAME with and without istration the balloon catheter was inflated to maintain renal perfusion pressure constant at control (pre+NAME) levels as constant renal perfusion pressure. The vehicle had no monitored via the femoral artery catheter. effect on either heart rate or blood pressure, but it did Protocol 3: effect of L-NAME on PRA, blood pressure, and result in a small but significant decrease in PRA (27 t heart rate with ,&adrenergic blockade and constant renal perfu9%, P < 0.05). A bolus injection of L-NAME increased sion pressure. The ability of inhibitors of EDRF synthesis to blood pressure by 20 t 7 mmHg, decreased heart rate by increase blood pressure and decrease heart rate (23) suggests 24 t 6 beats/min, and resulted in a 68.5 t 3.3% decrease sympathetic activity withdrawal, which could decrease renin in PRA (P < O.OOl), to a level of one-half that seen in the release. An additional set of experiments, using 36 rats, was run vehicle controls (Fig. 1). Not shown in Table 1, the reto control this variable. In these rats we injected a bolus of 1 sponse to a bolus of L-arginine resulted in blood pressure mg/kg body wt of the ,8-adrenergic blocker propranolol (Ayerst) returning to normal (107 t 3 mmHg), heart rate increasfollowed by a supplemental infusion of 0.3 mg kg body ing to 363 t 9 beats/min, and a slight but insignificant wt-l.h-’ for the duration of the experiment (22). The time increase in PRA to 4.6 t 1.7 ng ANG I ml-l 9h-l. Hecourse for these experiments was the same as described above. In this series of experiments three different groups of rats, all matocrit was unchanged and did not differ between the treated with propranolol, were studied. The first group of rats (n control and experimental groups. = 12) served as a time control and received neither an intraWhen renal perfusion pressure was maintained conaortic balloon catheter nor L-NAME. The second group of rats stant at control levels (Table l), L-NAME still resulted in (n = 12) received a bolus of L-NAME, and the change in blood a decreased heart rate as before (20 t 5 beats/min). When pressure was monitored. In the third group (n = 12), rats were renal perfusion pressure was maintained, L-NAME treatinstrumented with an intra-aortic balloon catheter. After Lment did not change PRA significantly (Fig. 1). NAME injection, the balloon catheter was inflated to maintain Effect of L-NAME on PRA, blood pressure, and heart constant renal perfusion pressure. Fifteen minutes after a conrate in propranolol- treated animals with and without constant renal perfusion pressure was achieved, heart rate was retrolling renal perfusion pressure. As shown in Table 2, corded and blood was sampled (treatment period). In the third ,&adrenergic blockade with propranolol resulted in a 21 t group with both P-blockade and constant renal perfusion pres2 mmHg decrease in blood pressure (P c 0.001) and a 38 sure after L-NAME, we concluded the protocol by giving the 300 l
l
l
l
Downloaded from www.physiology.org/journal/ajprenal by ${individualUser.givenNames} ${individualUser.surname} (132.210.236.020) on January 11, 2019.
F258
ENDOTHELIUM
AND
PLASMA
Table 1. PRA, RPP, and heart rate before and after L-NAME RPP,
RENIN
treatment
12
in presence
or absence of constant
Heart Rate, beats/min
mmHg
n
Vehicle
ACTIVITY
ng ANG
Control
Treated
Control
Treated
Control
102tl
101&l
335t5
33lt8
10.2t3.3
P
PRA, 1. ml-l
RPP
- h-l Treated
7.3t2.3 co.05
L-NAME
12
99&l
119&2
P
332t8
