EFFECTS OF CENTRAL LOSARTAN ON PLASMA-RENIN AND CENTRALLY MEDIATED NATRIURESIS

Effects of central losartan on plasma renin and centrally mediated nat riuresis. Because intracerebroventricular (ICV) infusion of hypertonic saline or angiotensin II (Ang II) both induce water drinking, vasopre ssin secretion, natriuresis and increased arterial pressure, the possi bility that common neural pathways mediate responses to ICV Ang II and hypertonic saline has been investigated. This was done by testing the effect of ICV infusion of the Ang II antagonist losartan on the natri uretic and presser responses to ICV hypertonic NaCl in sheep. The effe ct of ICV losartan on plasma renin concentration (PRC) was also invest igated. Infusion of losartan (1 mg/hr) into a lateral ventricle preven ted both natriuretic and presser responses to infusion of 0.6 mol/lite r NaCl into a lateral ventricle at 1 ml/hr. In another experiment, ICV losartan at 1 mg/hr caused a pronounced increase in the PRC of Na-dep leted sheep, while ICV Ang II at 3 mu g/hr decreased PRC. The results suggest that: (i) a central angiotensinergic pathway may mediate osmor egulatory responses to centrally administered hypertonic saline, and ( ii) a central angiotensinergic pathway may have a tonic inhibitory inf luence on renin secretion in Na-depleted animals.