Effect of Chlorpropamide on Osmotic Water Flow Across Toad Bladder and the Response to Vasopressin, Theophylline and Cyclic AMP1

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Abstract
The effect of chlorpropamide on the osmotic water flow across the urinary bladder of the toad Bufo marinus was studied. Chlorpropamide concentrations of 3 or 6 mm caused a small increase in osmotic water flow. Lower concentrations of chlorpropamide had no effect. Chlorpropamide concentrations as low as 0.03 mm potentiated the submaximal increase in osmotic water flow caused by vasopressin or theophylline. Low concentrations of vasopressin which had no physiological effect when added to control bladders caused a significant increase in osmotic water flow in the presence of chlorpropamide. Chlorpropamide inhibited the maximal or submaximal increase in osmotic water flow caused by cyclic AMP. This effect occurred at chlorpropamide concentrations of 0.3 mm or greater. The difference in the chlorpropamide concentration required for potentiation of the response to vasopressin and for inhibition of the response to cyclic AMP indicates that these are separate effects. These data support the hypothesis that an important effect of chlorpropamide in diabetes insipidus might be to potentiate the effect of small amounts of vasopressin.

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