Pregnancy: Activation of protein kinase C is required for oxytocin-induced contractility in human pregnant myometrium

Abstract

Intracellular mediators regulating the initiation of parturition are not 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 tyrosine kinase inhibitor, genistein. Phospholipase D activity was measured by employing the transphosphatidylation reaction. Staurosporine significantly reduced oxytocin-stimulated contractile activity with mean activity reduced by >50% following the addition of 10−6M staurosporine (P < 0.01), while addition of 10−5 M resulted in a measured mean contractile activity of −10% of the control (P < 0.001, n = 5). Similarly, uterine activity was minimal with oxytocin application following incubation with RO 31–8220, mean contractile activity being reduced by -40% by the addition of 10−7 M RO 31–8220 (P < 0.05) and by −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 oxytocin-induced contractile activity was observed (P < 0.01). Oxytocin evoked phospholipase D activation in a concentration- and time-dependent manner in cultured human pregnant myometrial cells (n = 4). These results indicate that activation of protein kinase C and tyrosine kinase are involved in the regulation of oxytocin-mediated myometrial contractile activity and that a coupled phospholipase D/phosphatidate phosphohydrolase pathway may play a role in the sustained stimulation of myometrial activity during labour.