vasopressin--1-(1-mercaptocyclohexaneacetic-acid)-2-(o--methyl-l-tyrosine)-8-l-arginine- and Hypertension--Renal

The contribution of neurohumoral factors to arterial pressure has been studied in several models of sodium-dependent hypertension including the deoxycorticosterone-saline, Dahl salt-sensitive rats, and reduced renal mass-saline. Observations from these animals have largely pointed to the sympathetic nervous system and arginine vasopressin (AVP) as the critical factors responsible for mediating the increased arterial pressure. Our work has indicated that the one-kidney, figure-8 renal wrap model of experimental hypertension is also sodium dependent. In these rats, prior sodium depletion prevented the development of hypertension whereas high sodium intake exacerbated the increase in arterial pressure. An activation of the sympathetic nervous system and increased AVP activity appeared to be responsible for the hypertension in rats maintained on normal and high sodium intake. Stimulation of the AVP and sympathetic nervous systems in sodium-dependent hypertension may be associated with a suppression of cardiovascular gamma-aminobutyric acid (GABA)-ergic function in the central nervous system. The inhibitory neurotransmitter, GABA, and an inhibitor of GABA uptake, nipecotic acid, lowered arterial pressure in a sodium-stimulated model of hypertension.

Topics: Animals; Arginine Vasopressin; Diet, Sodium-Restricted; gamma-Aminobutyric Acid; Humans; Hypertension; Hypertension, Renal; Neurotransmitter Agents; Nipecotic Acids; Proline; Saline Solution, Hypertonic; Sodium

We examined the response to hemorrhage in conscious normotensive and hypertensive rabbits under control conditions and during efferent blockade of 1) the hormones vasopressin (AVP) and angiotensin II (ANG II), 2) the autonomic nervous system, and 3) autonomic and hormonal inputs. We recorded mean arterial pressure, heart rate, and hindlimb conductance. The response to hemorrhage was unchanged with hormonal blockade alone. Blockade of the autonomic nervous system caused a faster rate of blood pressure decline, but the rate of decrease in hindlimb conductance was maintained at control levels. Blocking the autonomic nervous system and the hormones resulted in rapid blood pressure decline and an increase in hindlimb conductance. Although the three types of efferent blockade had a similar pattern of effects in normotensive and hypertensive rabbits, hypertensive rabbits exhibited less cardiovascular support during hemorrhage than normotensive rabbits. During hemorrhage, hypertensive rabbits had an attenuation of hindlimb vasoconstriction, a reduction in the heart rate-mean arterial pressure relationship, and reduced ability to maintain blood pressure compared with normotensive rabbits.

Topics: Analysis of Variance; Angiotensin II; Animals; Arginine Vasopressin; Autonomic Nervous System; Blood Pressure; Captopril; Female; Heart Rate; Hemorrhage; Hindlimb; Hypertension, Renal; Mecamylamine; Muscle, Skeletal; Norepinephrine; Rabbits; Regional Blood Flow; Regression Analysis

The contribution of the paraventricular nucleus region of the hypothalamus (PVN) to the maintenance of one-kidney, figure-8 renal wrap hypertension was determined in this study. Electrolytic ablation of the PVN was performed 4 wk after the production of hypertension or sham operation. Ablation of the PVN region significantly reduced mean arterial pressure (MAP) from 150 +/- 9 to 110 +/- 3 mmHg in the hypertensive rats. In the sham-hypertensive group, the lesion decreased MAP from 118 +/- 2 to 99 +/- 4 mmHg. In both groups of animals MAP from 118 +/- 2 to 99 +/- 4 mmHg. In both groups of animals MAP returned to prelesion values by day 7 postlesion. When ganglionic blockade was performed on day 7 postlesion, the fall in MAP was greater in hypertensive rats (-44 +/- 5 mmHg) than in normotensive rats (-26 +/- 3 mmHg). In a separate group of rats studied 3 days after PVN ablation, ganglionic blockade produced similar decreases in MAP in the wrapped and sham-operated animals. These studies suggest that the PVN contributes to the increased functional sympathetic nervous system associated with one-kidney, figure-8 renal hypertension. Although ablation of the PVN region decreases MAP, neural mechanisms compensate to return MAP to hypertensive levels.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Captopril; Chronic Disease; Heart Rate; Hypertension, Renal; Male; Paraventricular Hypothalamic Nucleus; Potassium; Rats; Rats, Inbred Strains; Reference Values; Sodium; Sympathetic Nervous System

Studies in sodium-dependent models of hypertension have shown that arginine-vasopressin (AVP) plays an important role in the maintenance of blood pressure, predominantly through its vasoconstrictor action. In addition to AVP, the sympathetic nervous system (SNS) also acts to maintain blood pressure in high sodium one-kidney, figure-8 renal wrap hypertension. The purpose of this study was to determine if chronic blockade of vascular AVP (V1) receptors affected the induction of high sodium renal hypertension and the contribution of the SNS to the maintenance of blood pressure. Rats receiving chronic s.c. administration of a V1 antagonist, d(CH2)5Tyr(Me)AVP, or vehicle were subjected to renal wrapping or sham surgery, V1 receptor blockade was confirmed periodically by an 80 +/- 3% reduction of the pressor response to a bolus injection of 10 mU/kg of AVP. d(CH2)5Tyr(Me)AVP did not affect the development of hypertension or the associated changes in plasma sodium, potassium, osmolality and hematocrit. In renal-wrapped rats, ganglionic blockade caused a greater fall in blood pressure in animals treated with d(CH2)5Tyr(Me)AVP than in vehicle-treated animals. However, this apparent increase in SNS function was not responsible for the hypertension in d(CH2)5Tyr(Me)AVP-treated, renal-wrapped rats, inasmuch as ganglionic blockade lowered blood pressure a similar amount in normotensive d(CH2)5Tyr(Me)AVP-treated, sham-operated rats and blood pressure remained elevated after combined blockade of the SNS, AVP and the renin-angiotensin systems. These results indicated that chronic blockade of V1 receptors did not alter the induction of high sodium renal hypertension and the mechanism of the elevated blood pressure was not through an activation of the SNS or other neurohumoral mechanisms.

Topics: Animals; Arginine Vasopressin; Atropine; Heart Rate; Hematocrit; Hexamethonium; Hexamethonium Compounds; Hypertension, Renal; Male; Osmolar Concentration; Potassium; Rats; Rats, Inbred Strains; Receptors, Angiotensin; Receptors, Vasopressin; Sodium

One-kidney, figure-8 renal wrapped and sham-operated rats maintained on high sodium intake were studied to determine plasma concentrations of vasopressin during the onset of hypertension. Animals were chronically prepared with femoral artery and vein catheters. Arterial blood samples were taken from conscious rats before and 3 days after renal wrap or sham operation while donor blood was simultaneously infused intravenously. Three days after surgery, arterial pressure, plasma osmolality and plasma vasopressin concentration increased significantly in the renal wrapped animals and remained unchanged in the sham-operated rats. Ganglionic blockade with hexamethonium and atropine produced equivalent decreases in arterial pressure and increases in plasma vasopressin concentration in the two groups of rats. Subsequent administration of the V1 vasopressin antagonist, d(CH2)5Tyr(Me)AVP, caused a significantly greater fall in arterial pressure in the hypertensive rats. These results provide further evidence for a contribution of vasopressin to sodium-dependent hypertension.

Topics: Animals; Arginine Vasopressin; Blood Pressure; Heart Rate; Hematocrit; Hypertension, Renal; Male; Osmolar Concentration; Potassium; Rats; Rats, Inbred Strains; Sodium; Vasopressins