DIFFERENTIAL-EFFECTS OF V(2) VASOPRESSIN AGONIST AND ANTAGONISTS ON BLOOD-PRESSURE REGULATION IN NORMOTENSIVE (WKY) AND SPONTANEOUSLY HYPERTENSIVE (SHR) RATS

The effects of arginine vasopressin analogs with V2 agonistic and antagonistic properties on blood pressure (BP) and heart rate (HR) were compared in conscious, spontaneously hypertensive (SHR) and normotensive (WKY) rats under resting conditions and after administration of phenylephrine (Phe) and sodium nitroprusside (SN). In WKY rats, resting BP and HR were not significantly affected during intravenous (i.v.) infusion of dVDAVP, (V2 agonist; 200 pg/kg/min), d(CH 2)5 (D-Ile2, Abu4]AVP(V2 antagonist 1 weak V1 antagonist; V2/V1 ratio = 29; 0.6-mu-g/kg/min), d(CH2)5[D-Ile2, Ile4, AlaNH2]AVP (V2 antagonist 2; very weak V1 antagonist; V2/V1 ratio = 83; 0.6-mu-g/kg/min) and combined infusion of V2 agonist and V2 antagonist 2. Under resting conditions BP and HR were not affected in WKY by any of the treatments. In SHR rats BP and HR were significantly decreased by V2 antagonist 2 infused alone or in combination with V2 agonist. In WKY but not in SHR V2 agonist without and with prior V2 receptors blockade significantly augmented bradycardia associated with a maximum increase of the systolic blood pressure after Phe administration. Significant differences were found between SHR and WKY in SN-induced changes of HR and BP after administration of V2 agonist and antagonists. The results suggest that circulating vasopressin may modify the baroreflex by interaction with receptors which are stimulated by V2 agonist but are different from the classical V2 receptors. The study supports evidence for differential effects of vasopressin analogs on blood pressure and blood pressure-heart rate relations in WKY and SHR.