Abstract
Acidic media have been reported to inhibit the hydro-osmotic effect of vasopressin in toad bladders, probably through inhibition of the cyclic AMP system. However, the mechanism of inhibition of the cyclic AMP system is controversial. Therefore, that inhibitory mechanism was further investigated in rat kidneys. The antidiuretic response to vasopression was significantly inhibited in animals with metabolic acidosis. The inhibition of the antidiuretic response was associated with a smaller than normal increase of urinary excretion of cyclic AMP after the iv injection of vasopressin. In in vitro experiments, both the increase of cyclic AMP concentration in renal medullary slices and the activation of adenylate cyclase in medulla by vasopressin were significantly less in acidic than in control media. These findings suggest that medabolic acidosis inhibits the antidiuretic effect of vasopressin by inhibiting the vasopressin-dependent cyclic AMP system in the kidney. Acidic media also inhibited cyclic AMP-phosphodiesterase. These dual effects of acidosis on adenylate cyclase and cyclic AMP-phosphodiesterase may explain the conflicting findings observed in the experiments on toad bladders.
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