Effects of intraventricular injection of Sar1-Ala8-angiotensin II on plasma vasopressin level increased by angiotensin II and by water deprivation in conscious rats

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Abstract
The effects of intraventricular [ivt.] injection of Sar1-Ala8-angiotensin II (a specific antagonist of angiotensin) on the plasma vasopressin level increased by ivt. angiotensin II injection and by H2O deprivation (46 h) were examined in conscious male rats with an indwelling cannula in the 3rd cerebral ventricle. Blood samplings were made by decapitation and the plasma vasopressin level was determined by radioimmunoassay. Twenty-five, 50 or 100 ng of angiotensin II produced significant (P < 0.05) increase in the plasma vasopressin level 90 s after the injection. The effect of 50 ng of angiotensin II was inhibited significantly (P < 0.05), at least with 100 ng of Sar1-Ala8-angiotensin II given 2 min before the angiotensin II injection. The dehydrated rats to which 1000 ng of Sar1-Ala8-angiotensin II was given 5 min before decapitation showed a significantly (P < 0.05) lower median plasma vasopressin level than the dehydrated controls. No significant difference in plasma osmolality was noted between them. The plasma vasopressin response to ivt. angiotensin II is apparently produced via angiotensin II receptors in the brain and Sar1-Ala8-angiotensin II inhibits the effect of endogenous angiotensin II on plasma vasopressin level during dehydration.

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