Effects of solute concentration on vasopressin stimulated cyclic AMP generation in the rat medullary thick ascending limbs of Henle's loop.

We examined effects of osmolality or sodium concentration on vasopressin induced cyclic AMP generation in the medullary thick ascending limbs isolated from collagenase treated rat kidneys. Vasopressin-stimulated cyclic AMP generation was increased as a function of NaCl concentration of the incubation medium. Addition of sucrose was also effective in enhancing the vasopressin-stimulated cyclic AMP, whereas addition of urea was without effect. When incubation medium was made hypertonic with sodium cyclamate, vasopressin-stimulated cyclic AMP generation was also enhanced. When choline chloride was used instead of sodium cyclamate, only an insignificant increase in the hormone-stimulated cyclic AMP generation was observed. These results suggest that the responsiveness of the rat medullary thick ascending limbs to vasopressin is regulated, at least in part, by transmembrane osmotic gradient.