Vasopressin dependent adenylate cyclase in single segments of rabbit kidney tubule

AVP dependent adenylate cyclase activity was measured in single pieces of 8 different tubular segments isolated from collagenase treated rabbit kidneys. High responses were observed in all the tested portions of the collecting tubule, that is its cortical branched part (BCT), its cortical straight part (CCT) and its outer medullary part (MCT). Dose response curves indicated in CCT: 2 fold threshold stimulation at 10(-11) M AVP, 27 fold stimulation at 10(-6) M AVP, half maximal stimulation at about 10(-9) M AVP. Both the medullary (MAL) and, to a lesser extent, the cortical (CAL) portions of the thick ascending limb were also observed to contain AVP sensitive adenylate cyclase (for MAL: 2 fold threshold stimulation at 10(-9) M AVP, 9 fold stimulation at 10(-7) M AVP, half maximal stimulation at 5 X 10(-9) M AVP). In contrast, nearly no responsiveness to AVP was observed in the proximal convoluted tubule, in the thin descending limb of the loop and in the distal convoluted tubule (DCT). The limited response obtained in DCT (which is a structure generally considered as a target site for AVP) as well as the clearcut effect elicited by AVP in MAL (the functioning of which is not known to be controlled by ADH) were expected observations; their possible physiological implications will be discussed.