Sodium-induced elevation of blood pressure in the anephric state.

Normotensive anephric rats infused with 2 milliliters of a hyperosmolar solution of either sodium chloride or mannitol showed an increase in arterial pressure that was very pronounced with the sodium chloride and that could be partly abolished by administration of an antagonist to the vasopressor action of antidiuretic hormone (ADH). Rats with congenital ADH deficiency subjected to the same treatment showed smaller increments in arterial pressure that remained unchanged after administration of the ADH antagonist. Expansion of intravascular fluid volume was similar in all four groups and bore no correlation to the change in arterial pressure. It is concluded that about half of the increase in blood pressure induced by saline was attributable to the vasopressor effect of stimulated ADH and the remainder to an additional sodium-related factor, since it was more pronounced in the saline-infused than in the mannitol-infused groups. Expansion of the intravascular volume per se could only account for a minimal part of the increment in pressure.

Reciprocation of renin dependency with sodium volume dependency in renal hypertension.

An angiotensin II inhibitor was administered to rats with two-kidney Goldblatt hypertension. The inhibitor produced a marked drop in blood pressure after 5 weeks but no significant change after 15 weeks of hypertension. However, even after 15 weeks of hypertension, following sodium depletion by either diuretics or a low sodium diet, the animals again became renin dependent as readministration of the inhibitor induced a significant fall in blood pressure. The data indicate that two-kidney Goldblatt hypertension is initially renin dependent but subsequently becomes sodium volume dependent in a way similar, although more protracted, to that already described for one-kidney Goldblatt hypertension.

Angiotensin-sodium interaction in blood pressure maintenance of renal hypertensive and normotensive rats.

A specific inhibitor of angiotensin II was used in rats to investigate whether angiotensin is involved in the maintenance of blood pressure in one-kidney Goldblatt hypertension, in which plasma renin levels are not usually increased. The inhibitor produced marked falls in blood pressure, often down to normal levels in the hypertensive animals only when they were depleted in sodium and not after sodium repletion. Much lesser but still significant falls in blood pressure were also produced in normotensive sodium-depleted rats but not in repleted rats. We conclude that the importance of angiotensin for maintaining blood pressure is largely determined by its relation to available sodium or fluid volume, since the renin component in maintenance of either the hypertensive or the normotensive state could be exposed only by sodium deprivation. Therefore, volume expansion per se or other pressor factors may be involved in maintaining blood pressure of these sodium-replete normotensive or hypertensive animals.

Renin-angiotensin system inhibition in conscious dogs during acute hypoxemia. Effects on systemic hemodynamics, regional blood flows, and tissue metabolism.

The role of the renin-angiotensin system in mediating the circulatory and metabolic responses to hypoxia was studied in three groups of conscious dogs that were infused continuously with normal saline, teprotide (10 mug/kg per min), and saralasin (1 mug/kg per min), respectively. Hypoxia was produced by switching from breathing room air to 5 or 8% oxygen-nitrogen mixture. Plasma renin activity increased from 2.3+/-0.4 to 4.9+/-0.8 ng/ml per h during 8% oxygen breathing, and from 2.8+/-0.4 to 8.4+/-1.8 ng/ml per h during 5% oxygen breathing. As expected, cardiac output, heart rate, mean aortic blood pressure, and left ventricular dP/dt and dP/dt/P increased during both 5 and 8% oxygen breathing in the saline-treated dogs; greater increases occurred during the more severe hypoxia. Teprotide and saralasin infusion diminished the hemodynamic responses to 5% oxygen breathing, but did not affect the responses to 8% oxygen breathing significantly. In addition, the increased blood flows to the myocardium, kidneys, adrenals, brain, intercostal muscle, and diaphragm that usually occur during 5% oxygen breathing were reduced by both agents. These agents also reduced the increases in plasma norepinephrine concentration during 5% oxygen breathing, but had no effects on tissue aerobic or anaerobic metabolism. In dogs pretreated with propranolol and phentolamine, administration of teprotide (0.5 mg/kg) during 5% oxygen breathing reduced mean aortic blood pressure and total peripheral vascular resistance, and increased cardiac output and heart rate, but did not affect left ventricular dP/dt, dP/dt/P, and end-diastolic pressure. Simultaneously, renal and myocardial blood flows increased and myocardial oxygen extraction decreased, while myocardial oxygen consumption did not change significantly. These results suggest that the renin-angiotensin system plays an important role in the hemodynamic responses to severe hypoxia. It appears that angiotensin not only exerts a direct vasoconstrictor action, especially upon the coronary and renal circulations, but also potentiates the cardiovascular effects of sympathetic stimulation that occur during severe hypoxia.

Renin-angiotensin system inhibition in conscious sodium-depleted dogs. Effects on systemic and coronary hemodynamics.

The role of the renin-angiotensin system in the regulation of the systemic and coronary circulations during sodium depletion was studied in conscious normotensive dogs by i.v. administration of teprotide (0.5 mg/kg), an angiotensin-converting enzyme inhibitor, and saralasin (0.05-5 mug/kg per min), an angiotensin-receptor antagonist. Sodium depletion was produced by administering a low sodium diet and furosemide for 5 days. Administration of both teprotide and saralasin lowered systemic arterial blood pressure and total peripheral vascular resistance. Simultaneously, cardiac output increased, but left ventricular end-diastolic pressure, dP/dt, and dP/dt/P did not change significantly. Furthermore, both agents reduced diastolic coronary vascular resistance and increased coronary blood flow, but did not affect myocardial oxygen consumption, left ventricular work, or myocardial efficiency. These systemic and coronary vasodilator effects of teprotide and saralasin, however, were not observed in normal dogs on a regular sodium diet; in this group, the only effect noted was a slight increase in arterial pressure during saralasin infusion. Arterial plasma concentration of norepinephrine did not differ between normal and sodiumdepleted dogs, nor did it change significantly after teprotide administration. These results suggest that, during salt depletion, angiotensin II exerts an active vasoconstrictor action on the systemic and coronary vessels, but has no significant effects on myocardial contractility or energetics. It also appears likely that the increase in cardiac output observed in sodiumdepleted dogs after angiotensin inhibition was caused, at least in part, by the decrease in systemic arterial pressure.

Conditioning effects of chronic infusions of dobutamine. Comparison with exercise training.

We studied the conditioning effects of chronic infusion of dobutamine and exercise training in three groups of chronically instrumented dogs. One group was infused with normal saline, a second group was infused with dobutamine (40 mug/kg per min), and the third group was exercised on a treadmill at 4 mph, up a 10 degrees incline. Each group was either infused or exercised for 2 h a day, 5 d a week for 5 consecutive wk. Resting heart rate and arterial blood lactate concentration, measured at weekly intervals, decreased progressively in the dobutamine and exercise groups, but not in the group that received normal saline infusion. Cardiovascular responses to submaximal treadmill exercise were not changed by 5 wk of normal saline infusion. However, the increases in heart rate, cardiac output, mean aortic blood pressure, arterial blood lactate, plasma renin activity, and norepinephrine concentration during exercise were significantly smaller after 5 wk of conditioning with either dobutamine or exercise training. After conditioning, the increases in arteriovenous oxygen difference during exercise were larger in the latter two groups, but the increases in total body oxygen consumption did not differ before and after conditioning. To assess ventricular function, we intravenously infused methoxamine both before and after conditioning. The slope of the line that related systolic aortic blood pressure and mean left atrial pressure increased in the animals conditioned with either dobutamine or exercise, indicating enhanced myocardial contractility. Left ventricular blood flow was lower in these two groups of animals than it was in the normal saline group. Left ventricular weight did not differ among the three groups. Our results show that chronic infusion of dobutamine produced cardiovascular and metabolic conditioning effects like those produced by exercise training, and further suggest that sympathetic stimulation during exercise plays a role in physical conditioning.

Insulin infusion in conscious dogs. Effects on systemic and coronary hemodynamics, regional blood flows, and plasma catecholamines.

Cardiovascular actions of insulin were studied by intravenous infusions of insulin (4 and 8 mU/kg per min) in normal conscious dogs. This resulted in increases in cardiac output, heart rate, and left ventricular derivative of pressure with respect to time (dP/dt) and dP/dt/P, as blood glucose was reduced. The inotropic and chronotropic effects of insulin were not related to hypoglycemia, as they persisted even when blood glucose was restored to control values or when it was prevented from falling by a simultaneous infusion of glucose. These cardiac effects were accompanied by increases in plasma catecholamines, and were abolished by propranolol pretreatment. Both plasma epinephrine and norepinephrine increased during insulin hypoglycemia, but only norepinephrine increased during insulin infusion when euglycemia was maintained. Mean arterial blood pressure did not change significantly during insulin hypoglycemia, but rose if euglycemia was maintained, probably due to the selective increase in norepinephrine in the latter condition. A pressor response also occurred in propranolol-pretreated dogs during insulin hypoglycemia, but was abolished when the animals also had been pretreated with phentolamine, indicating that the vasoconstrictor action of insulin was mediated via alpha adrenergic receptors. Insulin infusion increased left ventricular work and myocardial blood flow in dogs with and without hypoglycemia. Myocardial blood flow, however, did not change significantly during insulin infusion in dogs pretreated with propranolol. As propranolol also diminished the inotropic response, it appears that the increase in myocardial blood flow caused by insulin in the normal dog is causally related to the increased myocardial metabolic demand. Insulin also produced vasomotor effects on other vascular beds. In skeletal muscle, blood flow was increased under all study conditions, except during insulin hypoglycemia after propranolol-pretreatment when unopposed alpha-mediated vasoconstriction was present. The persistent increase in flow during both alpha and beta adrenergic blockade suggests that insulin has a direct dilator effect on skeletal muscle vasculature. In the adrenal gland, flow was increased except during euglycemia, when no rise in plasma epinephrine was observed, suggesting coupling between adrenal flow and catecholamine release. In the splanchnic bed, flow was decreased during euglycemia, when plasma norepinephrine rose, and during beta adrenergic blockade with propranolol, when unopposed alpha-mediated vasoconstriction also predominated. A similar pattern was found in the kidney, except that renal blood flow also fell after combined alpha and beta adrenergic blockade. The results show that the vasomotor effects on regional flows are mediated both via adrenergic mechanisms, and in the case of skeletal muscle and kidney, via mechanisms unrelated to sympathetic stimulation.

Vasoactive potential of the b(1) bradykinin receptor in normotension and hypertension.

The B(1) type receptor of bradykinin (Bk B(1)R) is believed to be physiologically inert but highly inducible by inflammatory mediators and tissue damage. To explore the potential participation of the Bk B(1)R in blood pressure (BP) regulation, we studied mice with deleted Bk B(2)R gene with induced experimental hypertension, either salt-dependent (subtotal nephrectomy with 0.5% NaCl as drinking water) or renin/angiotensin-dependent (renovascular 2-kidney-1-clip). Compared with the wild-type controls, the B(2)R gene knockout mice had a higher baseline BP (109.7+/-1.1 versus 101.1+/-1.3 mm Hg, P:=0.002), developed salt-induced hypertension faster (in 19.3+/-2.3 versus 27.7+/-2.4 days, P:=0.024), and had a more severe end point BP (148+/-3.7 versus 133+/-3.1 mm Hg, P:<0.05). On the contrary, renovascular hypertension developed to the same extent (149.7+/-4.3 versus 148+/-3.6 mm Hg) and in the same time frame (14+/-2.2 versus 14+/-2.1 days). A bolus infusion of a selective B(1)R antagonist at baseline produced a significant hypertensive response (by 11.4+/-2 mm Hg) in the knockout mice only. Injection of graded doses of a selective B(1)R agonist produced a dose-dependent hypotensive response in the knockout mice only. Assessment of tissue expression of B(1)R and B(2)R genes by reverse transcription-polymerase chain reaction techniques revealed significantly higher B(1)R mRNA levels in the B(2)R knockout mice at all times (normotensive baseline and hypertensive end points). At the hypertensive end points, there was always an increase in B(1)R gene expression over the baseline values. This increase was significant in cardiac and renal tissues in all hypertensive wild-type mice but only in the clipped kidney of the renovascular knockout mice. The B(2)R gene expression in the wild-type mice remained unaffected by experimental manipulations. These results confirm the known vasodilatory and natriuretic function of the Bk B(2)R; they also indicate that in its absence, the B(1)R can become upregulated and assume some of the hemodynamic properties of the B(2)R. Furthermore, they indicate that experimental manipulations to produce hypertension also induce upregulation of the B(1)R, but not the B(2)R, in cardiac and renal tissues.

Peptidyl dipeptidase in rabbit brain microvessels.

The activity of peptidyl dipeptidase (peptidyldipeptide hydrolase, EC 3.4.15.1), also known as angiotensin-converting enzyme, was studied in small blood vessel preparations isolated from rabbit brain. The vascular preparation contained arterioles and capillaries and was essentially free of extravascular material. Enzymatic activity was demonstrated in microvessel homogenates using both hippuryl-histidyl-leucine and tritium-labeled angiotensin I as substrates. Activity in the microvessels was dependent on the presence of chloride ion and was sensitive to inhibition by converting enzyme inhibitors previously shown to be effective in both vivo and in vitro. Specific activity in the micro-vessels was approximately 20 times that in homogenates of brain, and was almost 60% of that found in rat lung homogenates. The data were consistent with an endothelial localication for peptidyl dipeptidase in the cerebral vasculature and supports the proposal that this enzyme has a physiological role in extrapulmonary vascular beds.

A role for the A3 adenosine receptor in determining tissue levels of cAMP and blood pressure: studies in knock-out mice.

Adenosine administration has been reported to lower blood pressure by activating specific membrane receptors. The rat and human heart and aorta have been previously found to express both A2-type adenosine receptors, which activate adenylyl cyclase, and A3 adenosine receptors (A3AR), which inhibit adenylyl cyclase. In the current study, we used A3 adenosine receptor (A3AR) knock-out mice to examine the hypothesis that the relative levels of the A2-type adenosine receptors and A3AR determine the steady-state levels of cAMP in the cells and may affect blood pressure. We found that the A3AR knock-out mice express normal levels of the A1- and A2-type adenosine receptors. In situ hybridization demonstrated that the level of A3AR is high in the vascular smooth muscle layer of aortas derived from wild-type mice, but is not detectable in the knock-out mice. The steady-state level of cAMP is elevated in the aorta and heart of knock-out mice, as compared to wild-type mice, but is not altered in platelets, where A3AR is not expressed naturally. A3AR knock-out mice possess a blood pressure comparable to this in wild-type mice. However, when challenged with adenosine, the knock-out mice display a further increase in cAMP levels in the heart and vascular smooth muscle and a significant decrease in blood pressure, as compared to wild-type mice. In contrast, the effect of adenosine on ADP-induced platelet aggregation is similar in both types of mice. These studies indicate that the A3AR affects the steady-state level of cAMP in the tissues where it is naturally expressed, and that it influences the blood pressure in response to adenosine.

High level of expression of functional human platelet alpha 2-adrenergic receptors in a stable mouse C127 cell line.

We have generated, by transfection and proper selection, a stable mouse C127 cell line which expresses the human alpha 2-adrenergic receptor gene. The size of the mRNA produced by the cloned gene is 1.8 kb. Electrophoretic analysis and autoradiography of cell membrane proteins photoaffinity labeled with p-[3H]azidoclonidine gave a broad protein band of molecular mass of approx. 64 kDa. Saturation binding with [3H]rauwolscine as ligand gave an equilibrium dissociation constant of 1.29 +/- 0.46 nM (mean +/- S.D.) and binding capacity range of 18-35 pmol/mg membrane protein, with (3-6) x 10(6) receptors per cell. Antagonist competition experiments displayed the order of potency: yohimbine greater than rauwolscine greater than phentolamine much greater than prazosin. Agonist competitions demonstrated the order of potency: p-aminoclonidine greater than (-)epinephrine much greater than (+)epinephrine much greater than (-)isoproterenol. This pharmacological profile is characteristic of the human platelet alpha 2-adrenergic receptor. The expressed receptor is able to couple to the Gi protein. Thus, when epinephrine competition for specific binding of [3H]rauwolscine was performed in the presence of 1 mM MgCl2, 1 mM Gpp[NH]p increased the Ki for epinephrine from 164 to 315 nM. Following preincubation of cultures with 1 mM isobutylmethylxanthine, 1 microM epinephrine decreased forskolin-stimulated cellular cyclic AMP accumulation by 72%. The response was biphasic, and the attenuation effect disappeared at 100 microM epinephrine. A transfected clone which did not demonstrate detectable alpha 2-adrenergic receptor mRNA displayed low levels of alpha 2-adrenergic receptor, (less than 50 fmol/mg membrane protein), similar to those found in the parent C127 cell line. In this clone, epinephrine did not attenuate but, rather, enhanced forskolin-stimulated cyclic AMP accumulation. This new C127 cell line expressing high levels of alpha 2-adrenergic receptor provides an abundant source of a single human adrenergic receptor subtype in membrane-bound conformation which is able to couple to the Gi protein and inhibit forskolin-stimulated adenylate cyclase activity. This cell line will facilitate studies of the structure: function relationship of the alpha 2-adrenergic receptor and should aid in separating the components of various signal transduction mechanisms putatively attributed to this receptor.

Contribution of vasopressin to vasoconstriction in patients with congestive heart failure: comparison with the renin-angiotensin system and the sympathetic nervous system.

Ten patients with advanced congestive heart failure were treated with an arginine vasopressin V1 antagonist during hemodynamic monitoring to determine the contribution of vasopressin to vasoconstriction in this disorder. The vasopressin antagonist caused a decrease in systemic vascular resistance in the three patients whose plasma vasopressin was greater than 4.0 pg/ml (average for the group was 2.4 +/- 0.6). Plasma vasopressin concentration correlated with the percent decrease of systemic vascular resistance (r = 0.70, p less than 0.025), serum sodium (r = 0.72, p less than 0.02) and serum creatinine (r = 0.85, p less than 0.005). To compare the relative roles of vasopressin, the renin-angiotensin system and the sympathetic nervous system, these patients also received captopril and phentolamine. Captopril decreased systemic vascular resistance by 20% (p less than 0.05), mostly in patients with high plasma renin activity. Levels of plasma renin activity ranged between 1 and 46 ng/ml per h (average 14.7 +/- 5.7) and correlated with serum sodium (r = 0.77, p less than 0.025), serum creatinine (r = 0.73, p less than 0.025) and right atrial pressure (r = 0.67, p less than 0.05). Phentolamine decreased systemic vascular resistance in all patients (average 34%, p less than 0.01), but the decrease did not correlate with the pretreatment norepinephrine concentration. Norepinephrine levels were elevated in all patients (694 +/- 110 pg/ml) and correlated with baseline stroke volume index (r = 0.75, p less than 0.025) and plasma renin activity (r = 0.67, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Nonarrhythmogenicity of diuretic-induced hypokalemia. Its evidence in patients with uncomplicated hypertension.

Twenty patients aged 33 to 69 years with uncomplicated hypertension, no heart disease, and normal stress test results underwent ambulatory ECG monitoring a month after receiving placebo and two and four weeks after hydrochlorothiazide therapy. Serum potassium level (+/- SEM) averaged 4.4 +/- 0.09 mEq/L after the placebo trial and 3.4 +/- 0.07 and 3.0 +/- 0.06 mEq/L after two and four weeks of therapy, respectively. Sixteen patients had no arrhythmias. Four patients had 329 +/- 140 premature ventricular beats (PVBs) while receiving placebo and 341 +/- 203 and 315 +/- 158 PVBs per 24 hours after two and four weeks of therapy, respectively. Thus, patients with uncomplicated hypertension and no arrhythmias before diuretic therapy did not experience arrhythmias as a result of diuretic-induced hypokalemia of one month's duration. Patients with low-grade ventricular ectopy (VE) before therapy did not progress to higher grades of VE after diuretic treatment for four weeks.

Hypertension in a patient with hypercalcemia: captopril and verapamil.

A 38-year-old woman with hypercalcemia, severe hypertension, and high renin levels was treated with the angiotensin-converting enzyme inhibitor captopril. This therapy, together with spironolactone, normalized blood pressure (BP), but even with three daily administrations of the converting enzyme inhibitor, intermittent rebound hypertension could not be avoided. The administration of only verapamil, an antagonist of calcium transport, did not induce BP control, but when verapamil therapy was combined with administration of captopril and spironolactone, BP could be normalized with only twice-daily administration of the converting enzyme inhibitor. Thus, high plasma calcium levels seem to sensitize the arterioles to the intermittent increase of angiotensin II levels that accompanies captopril therapy.

Is elevated plasma renin activity of prognostic importance in progressive systemic sclerosis?

The pathologic lesions of the kidney in scleroderma in many respects resemble those of malignant hypertension, perhaps even in the absence of comparable blood pressure elevation. Because the malignant vascular changes have been related to hyperreninemia, we measured plasma renin activity in 23 patients with scleroderma with or without hypertension and/or renal failure. We found that high renin levels in most cases shortly preceded or coincided with a phase of sudden deterioration of the disease, characterized by a rapidly progressive renal failure. The outcome of this phase was invariably fatal, except for two patients in whom bilateral nephrectomy successfully arrested the rapid downhill course. These findings suggest that an unexplained increase in circulating renin levels in an otherwise stable patient with scleroderma may be taken as a possible marker of imminent deterioration requiring close monitoring and immediate therapeutic intervention.

Dilevalol in severe hypertension. A multicenter trial of bolus intravenous dosing.

Dilevalol, the R-R optical isomer of labetalol, a nonselective beta-antagonist with vasodilation from selective beta 2 agonism, was administered in sequential multiple bolus intravenous injections of 10 to 100 mg in total doses ranging from 35 to 585 mg (mean dose, 414 mg) to 101 patients with supine diastolic blood pressures above 120 mm Hg. Mean blood pressure was reduced from 200 (+/- 3)/129 (+/- 1) mm Hg to 149 (+/- 2)/101 (+/- 1) mm Hg, a mean reduction of 51/28 mm Hg. The therapeutic goal was established as a reduction in supine diastolic blood pressure to less than 100 mm Hg or a reduction of at least 30 mm Hg. This was achieved in 62 (61%) of 101 patients, with an additional 7 patients having a final supine diastolic blood pressure of 100 mm Hg. Treatment with dilevalol was less successful in black male patients than in the group at large. There was a tendency for older patients to respond better than younger patients. Prior recent treatment of patients with beta-adrenergic antagonists decreased the effectiveness of the drug. Significant orthostatic hypotension was not noted. Sixty-four patients were transferred to oral dilevalol treatment in combination with a diuretic, and blood pressure in this group averaged 160/100 mm Hg after 1 month of therapy. Dilevalol appears to be a safe and effective drug that can be used intravenously successfully in the majority of patients with severe hypertension and provides an alternative to therapy with other agents. It also is a useful agent for oral treatment of these patients after successful intravenous therapy.

Pressor systems in hypertension and congestive heart failure. Role of vasopressin.

Elevated peripheral vascular resistance, which characterizes hypertension and congestive heart failure (the latter regardless of absolute blood pressure level) is maintained to a large extent by the combined effects of three major neurohormonal pressor mechanisms: the renin-angiotensin system, the sympathoadrenal system, and arginine vasopressin. Blockade of one of these mechanisms may lead to compensatory stimulation of the others, thus offsetting in part the hemodynamic benefits of a specific intervention. Combination therapy, designed to attack all three systems (with use of an angiotensin converting enzyme inhibitor, a sympathetic blocker such as clonidine, and an antagonist of the vasopressor action of vasopressin), may help in the treatment of such cases. To illustrate this strategy, two experimental studies, one case of malignant hypertension, and one case of congestive heart failure are presented.

How does salt raise blood pressure? A hypothesis.

Existing data in the literature indicate that alpha 2-adrenergic receptor agonists have a profound hypotensive action, that sodium attenuates the affinity of alpha 2-adrenergic receptors for agonists, that the location of these receptors in the central nervous system is mainly at the sites of cardiovascular regulation, and that these sites exert a constant tonic inhibition of sympathetic vasoconstrictor tone. This article proposes the theory that sodium exerts its hypertensive action by decreasing the state of affinity of the alpha 2-adrenergic receptors of the central nervous system for locally occurring agonist neurotransmitters, which results in disinhibition of sympathoinhibitory neurons and leads to the hyperadrenergic state characteristic of salt-induced hypertension.

Angiotensin converting enzyme inhibitors. Properties and side effects.

The purpose of this brief review is to separate the characteristic properties and side effects attributable to the pharmacology of the whole class of angiotensin converting enzyme (ACE) inhibitors from those attributable to the chemical structure and kinetics of each particular ACE inhibitor. The former would be predictable and probably similar for all agents and, therefore, would be expected to recur with each agent, whereas the latter are likely to be characteristic of individual compounds and may be avoidable by changing to another compound with similar pharmacology but different molecular structure.

Contribution of bradykinin to maintenance of normal blood pressure.

The purpose of these experiments was to investigate whether the vasodilator tissue hormone bradykinin contributes to the maintenance of normal blood pressure. A newly synthesized peptide competitive antagonist of bradykinin, the compound Arg-Pro-Hyp-Gly-Phe-Ser-DPhe-Phe-Arg-trifluoracetic acid (B3852), capable of inhibiting the depressor effect of exogenous bradykinin by over 50%, was infused into 10 normotensive rats at a rate of 500 micrograms/0.1 ml/min. Blood pressure rose immediately, from a baseline of 104 +/- 5 to 131 +/- 7 mm Hg at the end of a 5-minute infusion, and returned to baseline within 2 to 3 minutes after discontinuation of the infusion. When similar doses were administered by continuous infusion to previously nephrectomized rats (n = 5) or as an acute bolus to adrenalectomized rats (n = 5), blood pressure rose from 111 +/- 3 to 125 +/- 5 mm Hg and from 112 +/- 4 to 128 +/- 5 mm Hg, respectively. The data suggest that a vasodepressor action of endogenous bradykinin contributes to maintenance of normal peripheral vascular tone, and that this action is not mediated through adrenal catecholamines or renomedullary prostaglandins.