Antidiuretic and Urinary Cyclic AMP Response of Vasopressin in Normal Rats and in Rats with Lithium‐polyuria

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Abstract
The antidiuretic and urinary cyclic [c]AMP response to supramaximal vasopressin infusion was studied in normal rats and in rats with Li-polyuria. The animals were anesthetized and then infused with a solution designed to produce excessive H2O diuresis and to lower basal cAMP excretion. In 6 control animals not infused with vasopressin (I) urinary cAMP excretion decreased during the infusion period. Vasopressin infusion (300 .mu.U[.mu.Units]/min) consistantly induced antidiuresis in all of 13 control rats (II); but the urinary cAMP response varied individually from a significant increase in 6 animals to either no change or to a decrease in the remaining animals. The antidiuretic response to vasopressin was inhibited by 85% in 10 animals with marked polyuria induced by Li administration (III). None of the animals in this group showed a significant increase of cAMP excretion in response to vasopressin. The average rate of cAMP excretion, which was equal in the 2 groups before vasopressin, was significantly lower in group III than in group II during vasopressin infusion. The increase in cAMP excretion during vasopressin antidiuresis, although not consistant, most likely reflected hormone-induced changes of intracellular cAMP levels in the renal medulla. The nephrogenic diabetes insipidus syndrome produced by Li was probably associated with a defect in the renal formation of cAMP in reponse to vasopressin.