[Effect of reserpine on the potency of alpha receptor blockers]

The influence of rather low doses of reserpine (0.125--2.0 mg/kg) on the pressor effect of noradrenaline (NA) was studied in pithed rats. In addition it was investigated whether the blocking activity of alpha-sympathicolytic agents is influenced by pretreatment with reserpine. 24 h after injection of these doses of reserpine this drug only increased the pressor effect of lower doses of NA without shifting the dose-response curve to the left. As a rule in rats pretreated with reserpine the affinity of alpha-blocking agents (derivatives of phenylethylamine and phenoxyethylamine) to alpha-adrenoceptors is not considerably altered. Only two phenylethylamine derivates substituted with a p-hydroxy group possessed considerably higher blocking activity in reserpine pretreated animals than in rats not pretreated. The increase in sensitivity of blood vessels against low doses of NA (250 pg and 1 ng) observed in rats pretreated with reserpine is abolished even by alpha-blocking substances with low affinity to alpha-adrenoceptors.