Enhanced renal vasoconstriction induced by vasopressin in SHR is mediated by V1 receptors

The development of hypertension in the spontaneously hypertensive rat (SHR) is associated with renal dysfunction; the observed renal vasoconstriction may reflect an imbalance of constrictor and dilator systems. The present studies evaluated renal vascular reactivity to arginine vasopressin (AVP) and mediation by V1 and/or V2 receptors. Renal blood flow (electromagnetic flowmetry) was measured in water-loaded, 8-wk-old SHR, Wistar-Kyoto rats (WKY), and Munich-Wistar rats. Injection of AVP (2 and 5 ng) into the renal artery caused dose-dependent renal vasoconstriction. The maximum blood flow response was approximately twofold larger in SHR than both normotensive strains. The strain difference was largely unaffected by indomethacin administration, although the reduction in blood flow produced by 5 ng AVP was 4-6% larger in both SHR and WKY during cyclooxygenase inhibition. The V1 receptor antagonist, [D-(CH2)5,Tyr(Me)2,Tyr(NH2)9]Arg8-vasopressin, blocked up to 90% of the renal vasoconstriction elicited by AVP. Intrarenal injection of the V1-receptor agonist [Phe2,Ile3,Org8]vasopressin produced renal hemodynamic effects similar to AVP; this agonist reduced renal blood flow, with twofold larger responses in SHR (-40 vs. -18% for 10 ng). In contrast, similar doses of the V2-receptor agonist 1-desamino-8-D-arginine vasopressin had no effect. These results indicate that AVP-induced vasoconstriction is mediated predominantly by the V1 receptor in the rat kidney. The enhanced vascular reactivity in 8-wk-old SHR may reflect an increased V1 receptor density and/or affinity or postreceptor signaling pathways, largely independent of buffering by the vascular V2 receptor or vasodilator prostaglandin activity. The strain difference in the vascular response to AVP may contribute to the renal vasoconstriction observed during the development of genetic hypertension.