Effect of dihydroergocristine on blood pressure and activity at peripheral alpha-adrenoceptors in pithed rats.

The effect of dihydroergocristine on blood pressure and peripheral alpha-adrenoceptors was examined in pithed rats. The pressor response to dihydroergocristine was reduced competitively by yohimbine and non-competitively by nifedipine, but not by prazosin or methysergide. These results show that vasoconstriction due to dihydroergocristine is mediated by alpha 2-adrenoceptors. Dihydroergocristine decreased the tachycardia elicited by electrical stimulation of the cardioaccelerator sympathetic nerves, this effect being antagonized by yohimbine. The pressor response to electrical stimulation of the spinal sympathetic outflow and to (-)-phenylephrine was reduced by dihydroergocristine suggesting competitive antagonism. It can be concluded that in pithed rats dihydroergocristine acts at the periphery as a competitive alpha 1-adrenoceptor blocker and an alpha 2-adrenoceptor agonist.