VASOCONSTRICTOR EFFECT OF ANGIOTENSIN AND VASOPRESSIN IN ISOLATED RABBIT AFFERENT ARTERIOLES

The present studies were performed to examine the vasoconstrictor effect of angiotensin II (ANG II), angiotensin III (ANG III), and vasopressin in isolated afferent arterioles of the rabbit kidney. Afferent arterioles were dissected together with their glomerulus and perfused with a pressure head of 120 cmH2O. Changes in vasomotor tone were assessed as diameter changes on videotaped recordings. Afferent arterioles responded to the angiotensins and vasopressin with dose-dependent reductions in vascular diameters with half-maximum responses being observed at concentrations between 10(-9) and 10(-8) M. Responses to ANG II and III were inhibited by saralasin. Contractile responses to ANG II and vasopressin were not altered by prior occlusion of the efferent arteriole, suggesting that afferent vasoconstriction does not represent a myogenic reaction to an increase in efferent resistance. The vasoconstrictor response to ANG II was largely eliminated by removal of the glomerulus and the distal-most portion of the afferent arteriole, whereas the response to vasopressin remained intact. Our data are consistent with the notion that the juxtaglomerular apparatus (JGA) and/or glomerulus may control proximal afferent arteriolar contractility by electrotonic or myogenic coupling mechanisms or by producing cofactors that modulate vasomotor responses.