Accentuation by angiotensin II of the antidiuretic and dipsogenic responses to intracarotid infusions of NaCl and fructose

Effect of intracerebroventricular deuterium oxide on water intake and AVP release induced by intravenous infusion of angiotensin II in sheep

The effect of intracerebroventricular (i.c.v.) infusion (0.02 ml min-1) of deuterium oxide (D2O), with NaCl added to isotonicity, on the water intake and arginine vasopressin (AVP) release caused by intravenous (i.v.) infusion of angiotensin II (AII) (4.8 nmol min-1) was studied in euhydrated sheep. The i.c.v. infusion of D2O, which started 80 min before commencement of the AII infusion, induced a water diuresis in four out of six animals and a measurable decrease in plasma AVP concentration. The i.v. infusion of AII effectively stimulated the AVP release and the response was unaffected by prior and simultaneous i.c.v. administration of D2O. However, the water intake measured 2 min after cessation of the AII administration was reduced by 50% when D2O was infused i.c.v. compared to that seen after simply the AII infusion. The inhibitory effect of D2O on AII-induced drinking disappeared rapidly after discontinuation of D2O administration. Compensatory increased drinking was seen during the first post-infusion hour, resulting in an equivalent cumulative intake of water at 60 min post-infusion in the two types of experiments. The present results support the idea that at least some of the cerebral effects of circulating AII on fluid balance are medicated via targets which are simultaneously accessible to influences from the blood and the cerebrospinal fluid.

Atrial natriuretic peptide (ANP) as a neuropeptide: interaction with angiotensin II on volume control and renal sodium handling

1. Angiotensin II (ANG II) and atrial natriuretic peptide (ANP) are functionally antagonistic circulating hormones involved in blood pressure and body fluid regulation. An inappropriate atrial secretion of ANP has been implicated in the pathogenesis of hypertension, but clinical and experimental results on the role of ANP in hypertension are still conflicting. 2. In the brain both peptides have been localized in close proximity, preferentially in areas involved in central cardiovascular, electrolyte and volume control. ANP was shown to inhibit ANG II-induced drinking, release of pituitary hormones and natriuresis, and to induce sodium retention when given alone. 3. These findings suggest that also in the brain ANG II and ANP exert functionally antagonistic effects. However, in contrast to their peripheral effects, ANG II induces natriuresis while ANP appears to cause antinatriuresis in the brain.

Angiotensin II and atrial natriuretic peptide in the brain: effects on volume and Na+ balance

Atrial natriuretic peptide (ANP) and angiotensin II (ANG II), although originally isolated from peripheral sources, are now known to be present in the central nervous system. The distribution of the peptides and their binding sites are found in areas involved in cardiovascular and volume/electrolyte regulation. Since ANP administered centrally can antagonize the actions of ANG II, the two peptides may function as opposing mechanisms involved in maintaining fluid and electrolyte homeostasis.

Potentiation of antidiuretic response to systemic angiotensin II by elevation of CSF NaCl concentration

The antidiuretic effect of the simultaneous intracerebroventricular (ICV) infusion of 0.24 M NaCl (0.02 ml/min) and intravenous (i.v.) infusion of angiotensin II (12 ng/kg X min) was studied in hydrated goats, and was compared to the antidiuretic effects of the separate infusions. The combined infusions inhibited the water diuresis for 30 min, whereas the separate infusions only reduced the water diuresis by 25% (ICV NaCl) and by 50% (i.v. angiotensin). The combined infusions increased the urine osmolality on the average by 415%. Corresponding increases induced by ICV NaCl and by i.v. angiotensin were 100 and 160%. The results suggest that systemic angiotensin II and elevated CSF NaCl concentration interact and potentiate each other as stimuli for antidiuretic hormone secretion. It is postulated that this synergism may help to preserve body water in hypovolemic conditions associated with hyperactivity of the renal renin-angiotensin system.

Drinking in goats as effect of simultaneous intravenous infusions of angiotensin (I or II) and hypertonic NaCl or mannitol

Drinking during the simultaneous intravenous infusion of angiotensin I (AI) or II (AII) and hypertonic NaCl or mannitol was studied in the goat, and was compared to the dipsogenic responses to the separate infusion of each of these four factors. Approximately the same amount of water was drunk during the infusion of AI/NaCl, AI/mannitol and AII/NaCl. The amount was roughly equal to the sum of the amounts taken when each of two paired stimuli was infused separately. Significantly less water was drunk in response to AII/mannitol. Somewhat more water was drunk during the separate AI than during the separate AII infusion. Administration of an AI converting enzyme inhibitor completely abolished the AI contribution to drinking during the AI/NaCl infusion but did not reduce AII/NaCl drinking, indicating that the response to AI was entirely due to its conversion into AII. The possibility is discussed that the considerable difference between AI/mannitol and AII/mannitol drinking might have been the result of choroidal and/or ependymal AI converting enzyme activity.

The effect of intravenous infusion of angiotensin II on drinking in the Australian marsupial Trichosurus vulpecula

1. When marsupial brush-tailed possums were maintained on a normal fruit and vegetable diet with access to water ad libitum, I.V. infusion of synthetic angiotensin II at rates of 0.035-3.5 mug/kg. min caused short-latency drinking in up to seven of eleven animals tested. These rates also had significant pressor effects.2. There was a positive correlation between the rate of angiotensin infusion and the percentage of tested animals which responded by drinking, as well as the amount of water drunk by such animals. The amount drunk during a second infusion 1 hr later was reduced. There was a negative correlation between the rate of infusion and the latency to drinking.3. Of six animals given access to both water and 1.8% sodium chloride solutions, five drank some saline during maintenance and control periods and all responded with short-latency drinking of water to infusion of angiotensin II at 0.35 mug/kg. min.4. Withdrawal of 10% of blood volume, known to stimulate renin production in the possum, caused an increase in water intake in only one of six possums.5. Infusion of isoprenaline I.V. at 20 mug/kg. min, which caused a profound fall in B.P., had no effect on drinking by all six possums.6. It is concluded that these marsupials share with eutherian mammals responsiveness to a dipsogenic action of angiotensin II, which appears to be inhibited by preceding ingestion of water and potentiated by preceding ingestion of hypertonic saline. The physiological significance of this effect is uncertain.

Is vasopressin involved in the pathogenesis of malignant desoxycorticosterone hypertension in rats?

Rats with unilateral nephrectomy were offered 1% sodium chloride as drinking fluid and were injected with desoxycorticosterone trimethylacetate (D.O.C.-T.M.A.) at weekly intervals. During the fourth to seventh week after the start of the experiment, malignant hypertension developed in most of the animals: body weight fell, reflecting volume depletion; serum osmolality and serum sodium and urea concentrations increased; in the kidneys malignant nephrosclerosis occurred. In such animals, plasma concentrations of arginine-vasopressin were increased ten-fold in comparison with control animals; intravenous injection of a specific vasopressin antibody resulted in a transient fall of blood-pressure (B.P.) to normal or subnormal levels, while the injection of an angiotensin-I or angiotensin-II antibody did not affect B.P. In control animals none of the antibodies had an effect on B.P. It is concluded that in the pathogenesis of malignant D.O.C. hypertension vasopressin plays a role similar to that of renin-angiotensin in malignant renal hypertension.

Angiotensin stimulated AVP-release in humans

Release of arginine vasopressin (AVP) from rat neurohypophysis in in vitro studies is significantly augmented by the addition of angiotensin (A-II), and in in vivo studies in dogs renin and A-II were found to stimulate secretion of AVP. Both these results suggest the existence of a direct relationship between the salt regulating renin-angiotensin-aldosterone system and the water controlling AVP system. To evaluate whether such observations apply also in man a sensitive double antibody radioimmunoassay for AVP was developed [17, 18]. Basal plasma levels of AVP in recumbent humans without salt and fluid restriction at room temperature were 3.4 plus or minus 2.2 pg/ml, and 30 min after the onset of an A-II infusion at a concentration of 3-30 ng/min-kg, a significant increase of AVP was found. Maximum measurements were 2-5 times basal levels which returned to normal within 90 min. During the A-II infusion one also noted a 20 mm Hg rise in blood pressure, accompanied by a significant decrease in plasma renin activity. During the same period serum osmolality and serum sodium concentration did not change. Elevation of blood pressure by norepinephrine was not followed by any detectable change of plasma AVP levels, thus excluding a nonspecific blood pressure effect.