• J Ascher-Landsberg, T Saunders, and M Phillippe.
• Department of Obstetrics and Gynecology, University of Chicago, IL 60637, USA.
• Am. J. Obstet. Gynecol. 2000 Apr 1;182(4):943-9.

ObjectiveThe role of diacylglycerol in the phosphatidylinositol-signaling pathway is to activate protein kinase C. In the myometrium, protein kinase C activation leads to inhibition of phasic contractions. These studies are designed to determine why stimulation of the phosphatidylinositol-signaling pathway caused by oxytocin does not cause a paradoxical suppression of contractions through diacylglycerol production and protein kinase C activation. Specifically, these studies were performed to test the hypothesis that diacylglycerol catabolism is significant in myometrial tissue, thereby precluding its availability for the activation of protein kinase C.Study DesignFor these studies, uterine tissue was obtained from Sprague-Dawley rats both nonpregnant and with timed gestations. In vitro contraction studies were performed with cumulative additions of oxytocin (8-64 nmol/L) with and without R59022 (a diacylglycerol kinase inhibitor) or RHC80267 (a diacylglycerol lipase inhibitor). The contraction data were computer-digitalized, analyzed for total contractile activity, normalized for tissue cross-sectional area, and reported as the percentage of spontaneous activity.ResultsIn myometrium from nonpregnant animals, inhibition of diacylglycerol lipase with RHC80267 had little effect on oxytocin-stimulated contractile activity, whereas inhibition of diacylglycerol kinase with R59022, although producing an increase in contractile frequency, markedly suppressed total oxytocin-stimulated contractile activity. In contrast, in myometrium from near-term pregnant animals both RHC80267 and R59022 produced marked suppression of oxytocin-stimulated contractile activity.ConclusionsThese studies have demonstrated that prevention of diacylglycerol degradation, especially in response to inhibition of myometrial diacylglycerol kinase, results in the paradoxic oxytocin-mediated suppression of total myometrial contractile activity. These observations support the hypothesis that, when its catabolism is prevented, diacylglycerol produced in response to stimulation of the phosphatidylinositol-signaling pathway by oxytocin becomes available for protein kinase C activation, resulting in inhibition of myometrial contractile activity.

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