INFLUENCE OF ACETONYLGERANIIN, A HYDROLYZABLE TANNIN FROM EUPHORIA-LONGANA, ON ORTHOSTATIC HYPOTENSION IN A RAT MODEL

Acetonylgeraniin, an active principle isolated from the seeds of Eupho ria longana Lam. (Sapindaceae), reversed the fall in arterial blood pr essure in conscious hypertensive rats (SHRs) with orthostatic hypotens ion induced by injection of hexamethonium into animals subjected to 90 degrees head-up tilts for 60 seconds. However, acetonylgeraniin faile d to affect prazosin-induced orthostatic hypotension. Plasma noradrena line (NA) and mean blood pressure were elevated dose-dependently by an intravenous injection of acetonylgeraniin into the rats; this increas e in blood pressure was totally abolished by prazosin. Failure of hexa methonium or pentolinium, the blockers of ganglionic nicotinic recepto rs, to influence the NA releasing action of acetonylgeraniin ruled out the participation of ganglionic stimulation. This NA-releasing action of acetonylgeraniin was, however, totally abolished by the inhibitors of noradrenergic nerve terminals, guanethidine or bretylium. Also, th e activity of this tannin was not modified by adrenalectomy. Thus, a d irect release of NA from the noradrenergic nerve terminals by acetonyl geraniin seems responsible for the reversing of orthostatic hypotensio n.