Stimulatory cholinergic effect on the release of antiaggregatory activity into the circulation of cat and man and its modification by beta-adrenergic antagonists.

The release of PGI2-like activity into the circulation in response to cholinergic agonists and modification of this response by beta-adrenergic antagonists was investigated in anaesthetized cats and healthy humans. Antiaggregatory activity in the arterial blood was continuously assayed by measuring platelet aggregation on blood superfused collagen strip. In some of the human experiments, after the administration of the drugs, the conversion of [14C]-arachidonate to [14C]-prostaglandins in the pulmonary vascular bed was studied. Cholinergic agonists stimulated the release of PGI2-like activity into the circulation, which effect was potentiated in cats by beta-adrenergic antagonists. In humans the latter agents did not stimulate the conversion of [14C]-arachidonate to prostaglandins in the pulmonary circulation and, moreover, inhibited the stimulatory cholinergic effect. The results suggest that an interplay between cholinergic and beta-adrenergic mediators may be involved, although in a different way in cats and in humans, in the release of PGI2-like activity into the systemic circulation.