Sympathomimetic effects of Parquetina nigrescens (Periplocaceae) extract in isolated portal vein smooth muscle.

摘要

The purpose of this study was to examine the mechanisms underlying the pharmacological effects of the extract of Parquetina nigrescens (Expar) on vascular smooth muscle contractility. To evaluate the Expar effect, the contractile activity of portal veins isolated from Wistar Kyoto rats was isometrically recorded. Isolated portal vein preparations developed rhythmic and spontaneous contractile activity. Expar increased the contractile response of the portal vein preparations in a dose-dependent manner. The maximal effect of the dose-response curve for Expar was prevented by the alpha1-adrenergic blocking agent prazosin at 10 nM and 30 nM concentration dependently. The contractile responses of the muscle to Expar were partly blocked after chemical sympathectomy of the preparations with 6-hydroxydopamine, and those obtained in the same conditions with tyramine were completely abolished, whereas responses to noradrenaline were unaffected by the 6-hydroxydopamine pretreatment. It is concluded that Expar contains principles, which can be characterized as direct and indirect sympathomimetic.