Renal microvascular effects of vasopressin and vasopressin antagonists

The effects of vasopressin (AVP) and vasopressin antagonists on lumen diameters of cortical afferent and efferent arterioles isolated from rabbit kidneys were examined. Over a concentration range of 10(-14) to 10(-7) M, AVP had no effect on lumen diameters of afferent arterioles, although the arterioles were responsive to norepinephrine. Similarly, addition of 10(-8) M AVP to the lumen of afferent arterioles or to the bath of arterioles pretreated with indomethacin had no effect. In contrast, AVP caused a concentration-dependent reduction of lumen diameters of efferent arterioles. AVP was approximately 100-fold more potent than norepinephrine in producing contraction of efferent arterioles. The V1-selective antagonist, [d(CH2)5Tyr(Me)]AVP, and the V1/V2-antagonist, d(CH2)5D-Tyr(Et) desGlyVAVP, inhibited the vasoconstriction produced by AVP in a concentration-dependent but noncompetitive manner. The V2-selective antagonist, [d(CH2)5D-Ile]VAVP, had no significant effect on AVP-induced vasoconstriction. We conclude that, under the in vitro conditions used, AVP selectively contracts efferent arterioles. The results provide direct evidence for a postglomerular vascular effect of AVP in the renal cortex. This activity, together with its previously described effects on the glomerulus, suggests that AVP may produce changes in glomerular function and/or peritubular forces that are involved in tubular reabsorption.