THE SEPARATE UTEROTONIC AND PROSTAGLANDIN-RELEASING ACTIONS OF OXYTOCIN - EVIDENCE AND COMPARISON WITH ANGIOTENSIN AND METHACHOLINE IN THE ISOLATED RAT UTERUS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 213  (3) , 575-579
Abstract
Both oxytocin (OT) and prostaglandin (PG) have potent uterotonic activity. The uterotonic action of OT may be mediated by PG release. The uterotonic and PG-releasing actions of OT, angiotensin II (AT) and methacholine (MC) were studied in isolated pregnant rat uteri. OT-induced PG release is a direct effect of OT and not a secondary response to myometrial contractions and that the uterotonic action of OT is not dependent on PG participation. Equipotent uterotonic doses of OT, AT and MC had different effects on uterine PG release. OT and AT caused uterine contractions and PG release, but MC caused contractions but no PG release. OT produced a dose-dependent uterotonic response. There was no proportional relationship between the magnitude of uterine contractions and the rate of PG release. In uterine homogenates, which lack the functional integrity for mechanical contractions, OT caused an increase in PG biosynthesis. Indomethacin suppressed both the spontaneous and the OT-stimulated PG synthesis in the uterine homogenates. In isolated uterine horns, the contractile response to OT was attenuated in the presence of indomethacin sufficient to inhibit completely the OT-stimulated PG synthesis. OT has a dual action in the uterus and may act on 2 different receptors, one leading to myometrial contractions and the other leading to PG release. AT, an octapeptide like OT, may have a dual action, but the parasympathomimetic, MC, has predominately a direct uterotonic action.