ACTIVATION OF PROTEIN-KINASE-C IS REQUIRED FOR OXYTOCIN-INDUCED CONTRACTILITY IN HUMAN PREGNANT MYOMETRIUM

Intracellular mediators regulating the initiation of parturition are n ot fully understood, This study was designed to determine the possible mechanism of oxytocin-induced uterine contractility during labour, In -vitro isometric contraction studies were performed with longitudinal strips of human pregnant myometrium in the presence and absence of the protein kinase C inhibitors, staurosporine and RO 31-8220, and the ty rosine kinase inhibitor, genistein, Phospholipase D activity was measu red by employing the transphosphatidylation reaction. Staurosporine si gnificantly reduced oxytocin-stimulated contractile activity with mean activity reduced by >50% following the addition of 10(-6) M staurospo rine (P < 0.01), while addition of 10(-5) M resulted in a measured mea n contractile activity of similar to 10% of the control (P < 0.001, n = 5), Similarly, uterine activity was minimal with oxytocin applicatio n following incubation with RO 31-8220, mean contractile activity bein g reduced by similar to 40% by the addition of 10(-7) M RO 31-8220 (P < 0.05) and by similar to 87% by the addition of either 10(-6) or 10(- 5) M (P < 0.01, n = 3). Conversely, addition of genistein (10(-7) and 10(-6) M) had little effect on oxytocin-induced contractions, although at a higher concentration (10(-5) M) a significant reduction in oxyto cin-induced contractile activity was observed (P < 0.01), Oxytocin evo ked phospholipase D activation in a concentration- and time-dependent manner in cultured human pregnant myometrial cells (n = 4), These resu lts indicate that activation of protein kinase C and tyrosine kinase a re involved in the regulation of oxytocin-mediated myometrial contract ile activity and that a coupled phospholipase D/phosphatidate phosphoh ydrolase pathway may play a role in the sustained stimulation of myome trial activity during labour.