Effect of vasopressin and V1 receptors blockade on hypotensive action of ANP in normotensive [WKY] and spontaneously hypertensive rats

The aim of the study was to find out whether vasopressin (AVP) modifies hypotensive and heart rate accelerating effects of atrial natriuretic peptide (ANP) in normotensive (WKY) and spontaneously hypertensive (SHR) conscious rats. The effect of i. v. administration of 1; 2 and 4 µg of ANP on blood pressure (MP) and heart rate (HR) was compared during i. v. infusion of 0.9% NaCl (NaCl), NaCl + AVP (1.2 ng kg⁻¹ min⁻¹) and NaCl + dEt₂ AVP (V₁ receptors antagonist, 0.5 µg kg⁻¹ min⁻¹). AVP increased MP in SHR and WKY and decreased HR in SHR. V₁ antagonist decreased MP and increased HR only in SHR. In SHR ANP decreased MP and increased HR during NaCl, AVP and V₁ antagonist infusion. In WKY these effects were observed only during AVP administration. In each experimental situation hypotension and tachycardia induced by ANP were greater in SHR than in WKY. In both strains ANP induced changes in MP and HR were enhanced during AVP in comparison to NaCl infusion. V₁ antagonist did not modify effects of ANP in WKY and SHR. The results indicate that ANP abolishes hypertensive response induced by blood AVP elevation and that the basal levels of endogenous vasopressin acting through V₁ receptors does not interfere with hypotensive action of ANP neither in WKY nor in SHR.