Hypotension and thirst in rats after phentolamine treatment

Abstract

Administration of the α-adrenergic receptor blocker phentolamine is known to lower arterial blood pressure and to increase renin secretion and water intake in rats. In the present experiments, drinking by rats after subcutaneous administration of the drug was found to be inversely related to arterial blood pressure within the range of 60–90 mm Hg. Drug treatment in nephrectomized rats led to such severe hypotension that drinking was precluded. Pretreatment with propranolol moderated the hypotension in nephrectomized rats and drinking was not attenuated. These results parallel those of previous experiments using the β-adrenergic receptor agonist isoproterenol. Collectively, they suggest that after treatment with these hypotensive agents, a stimulus for thirst can arise from some factor other than angiotensin. This stimulus, perhaps mediated by arterial baroreceptors, is additive in its effects on thirst with the stimulus induced by hypertonic NaCl or subcutaneous colloid treatments.