Somatostatin: an endogenous peptide in the toad urinary bladder inhibits vasopressin-stimulated water flow.

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Abstract
Somatostatin (somatotropin release-inhibiting factor; SRIF) is a tetradecapeptide present in brain, pancreas, gastrointestinal tract and thyroid that inhibits the secretion or action of several hormones in these tissues. The toad urinary bladder contains concentrations of endogenous somatostatin (8.0 pg/.mu.g protein) comparable to those found in the mammalian pancreas and gastrointestinal tract. To determine if somatostatin directly alters the action of vasopressin the effects of this polypeptide on vasopressin-stimulated transport processes in the toad urinary bladder were studied in vitro. Somtostatin produced a dose-dependent, reversible inhibition of vasopressin-stimulated osmotic H2O flow; it inhibited theophylline-stimulated H2O flow but not the H2O flow stimulated by 8-p-chlorophenylthio cAMP. The data are consistent with an inhibition of both basal and hormone-stimulated adenylate cyclase. Vasopressin-stimulated short circuit current was not inhibited by somatostatin. Direct evidence is provided for an effect of somatostatin on hormone-modulated epithelial transport in tissues other than the gastrointestinal tract. Endogenous somatostatin may function as a local regulator of the cellular action of vasopressin on osmotic H2O flow.