Endogenous prostaglandin formation in the field-stimulated guinea-pig vas deferens: comparison of the inhibitory effects of indomethacin and NS-398

Abstract

Prostaglandin (PG) E2inhibited both phases of contraction produced by electrical field stimulation of the guinea-pig vas deferens. PGF2αand PGD2were without effect on this preparation. Carbacyclin (a PGI2) analogue inhibited the first phase of contraction at higher concentrations, whereas U46619 (a thromboxane mimetic) potentiated both phases of contraction. As exogenous arachidonic acid inhibits both phases of contraction of the electrically field-stimulated guinea-pig vas deferens, it is likely that the arachidonic acid is converted to PGE2in the vas deferens. Indomethacin, a non-specific inhibitor of prostaglandin H synthase (PGHS), attenuated the inhibitory actions of exogenous arachidonic acid when examined on the first phase of contraction. NS–398, a relatively specific inhibitor of PGHS–2, also prevented the inhibitory action of exogenous arachidonic acid. However, NS–398 was much less effective than indomethacin in this respect even though NS–398 and indomethacin inhibit PGHS–2 with similar potencies. Consequently, the findings suggest that exogenous arachidonic acid is converted to PGE2in the guinea-pig vas deferens by the actions of PGHS–1 and, to a lesser extent, by PGHS–2.