Potentiation by SKF 525A of the pressor responses to catecholamines, oxytocin and carotid occlusion in rats.

The effect of SKF 525A (20 mg/kg i.v.) on pressor responses of various origin was studied. SKF 525A abolished or markedly reduced the pressor responses to ganglionic stimulants (DMPP and McN-A-343), but potentiated those to noradrenaline (in normal and pithed animals), adrenaline, tyramine, oxytocin and carotid occlusion. After recovery of the pressor effect of McN-A-343 from the SKF 525A-induced suppression, the pressor effect of noradrenaline was still further enhanced. The abolition of the pressor responses to ganglionic stimulants is due to the ganglion and adrenal-medullary blocking action of SKF 525A. This action of SKF 525A is of secondary importance for its potentiating effect. It is tentatively suggested that for the SKF 525A-induced potentiation a partial depolarization of arterial smooth muscle membrane resulting from a prolonged release of subthreshold concentrations of catecholamines from tissue stores, may be of primary importance.