Extended mepyramine treatment and histamine H1-receptors in guinea-pig brain.

Treatment of guinea-pigs for 24 days with a single daily dose of mepyramine, 5 mg/kg i.p. had no consistent significant effect on the number of histamine H1-receptors, determined from the promethazine-sensitive binding of [3H]mepyramine, in cerebellum, cerebral cortex, hippocampus, hypothalamus or intestinal smooth muscle. Measurement of the time course of the block of H1-mediated blood pressure responses in conscious guinea pigs following a single i.p. injection of mepyramine, 5 mg/kg, suggested that some degree of block persisted for up to 16 h. Treatment of guinea pigs with two daily doses of 5 mg mepyramine/kg, i.p., for 10 days had no consistent effect on the KD or capacity of promethazine-sensitive [3H]mepyramine binding to cerebellum or hypothalamus.