PGH2, TxA2 and PGI2 have potent and differentiated actions on human uterine contractility

The contractile response to three different prostanoids of the isolated human myometrium and the different layers of the uterotubal junction (UTJ) was studied in vitro. The prostaglandin endoperoxide, PGH2, stimulated contractility of both the myometrium and the outer and inner muscle layers of the UTJ, whereas the intermediate layer of the UTJ was inhibited. Thromboxane A2 generated from PGH2 and a thromboxane synthase preparation caused a stimulation of both the myometrium and all three layers of the UTJ. The stimulatory response to TxA2 occurred at concentrations as low as 50-70 pg/ml. The sodium salt of PGi2 was found to relax both the myometrium and all the layers of the UTJ. Intravenous administration of PGI2 in repeated doses between 2-8 microgram induced facial flushing and headache but had little if any effect on in vivo uterine contractility. At least under in vitro conditions, these short-lived prostanoids and/or their metabolites apparently have a specific action on uterine contractility, an action which is manifested at comparatively low concentrations.