Augmentation by chlorpropamide of 1-deamino-8-D-arginine vasopressin-induced antidiuresis and stimulation of renal medullary adenylate cyclase and accumulation of adenosine 3',5'-monophosphate.

The effect of chlorpropamide was determined in Brattleboro diabetes insipidus (DI) rats that were injected with 1-deamino-8-D-arginine vasopressin (dDAVP). Chlorpropamide augmented the antidiuretic responses to 0.78 and 1.56 ng dDAVP but not to larger doses. In an effort to explain this observation we investigated the effect of chlorpropamide on renal medullary adenylate cyclase activation by dDAVP and on phosphodiesterase activity. We found that the injection of chlorpropamide increased adenylate cyclase activation by dDAVP added in vitro to renal medullary cell membrane preparations from Brattleboro DI rats but had no effect on phosphodiesterase activity. When kidneys from Brattleboro DI rats, treated and not treated with chlorpropamide, were perfused in vitro, we found that 10(-4) M dDAVP increased the concentration of cAMP in comparison to untreated and chlorpropamide-treated groups, and that chlorpropamide plus dDAVP resulted in a greater concentration of renal cAMP than was found with dDAVP alone. We believe that treatment with chlorpropamide increases dDAVP-stimulated renal medullary adenylate cyclase activity without altering phosphodiesterase activity and that this leads to increased renal cAMP concentrations. This, in turn, causes an augmented antidiuresis in response to dDAVP.