Influence of arginine vasopressin receptors and angiotensin receptor subtypes on the water intake and arterial blood pressure induced by vasopressin injected into the lateral septal area of the rat

Abstract

In this study we investigated the influence of d(CH₂)₅-Tyr(Me)-[Arg⁸]vasopressin (AAVP) and [adamanteanacetyl¹,0-ET-d-Tyr²,Val⁴,aminobutyryl⁶,Arg^8,9]-[Arg⁸]vasopressin (ATAVP), which are antagonists of vasopressin V₁ and V₂ receptors, and the effects of losartan, a selective angiotensin AT₁ receptor antagonist, and CGP42112A, a selective AT₂ receptor antagonist, injected into the lateral septal area (LSA) on thirst and hypertension induced by [Arg⁸]vasopressin (AVP). AAVP and ATAVP injected into the LSA reduced the drinking responses elicited by injecting AVP into the LSA. Both the AT₁ and AT₂ ligands administered into the LSA elicited a concentration-dependent decrease in the water intake induced by AVP injected into the LSA, but losartan was more effective than CGP42112A. The increase in MAP, due to injection of AVP into the LSA, was reduced by prior injection of AAVP from 18±1 to 6±1 mm Hg. Losartan injected into the LSA prior to AVP reduced the increase in MAP to 7±0.8 mm Hg. ATAVP and CGP42112A produced no changes in the pressor effect of AVP. These results suggest that the dipsogenic effects induced by injecting AVP into the LSA were mediated primarily by AT₁ receptors. However, doses of losartan were more effective when combined with CGP42112A than when given alone, suggesting that the thirst induced by AVP injections into LSA may involve activation of multiple AVP and angiotensin II receptor subtypes. The pressor response of AVP was reduced by losartan and by AAVP. CGP42112A and ATAVP did not change the AVP pressor response. These results suggest that facilitator effects of AVP on water intake are mediated through the activation of V₁ receptors and that the inhibitory effect requires V₂ receptors. The involvement of AT₁ and AT₂ receptors can be postulated. Based on the present findings, we suggest that the AVP in the LSA may play a role in the control of water and arterial blood pressure balance.