Oxytocin activates mitogen-activated protein kinase and up-regulates cyclooxygenase-2 and prostaglandin production in human myometrial cells

OBJECTIVE: The objective of our study was to test the hypothesis that oxyto cin promotes prostaglandin production by up-regulating cyclooxygenase-2 via activation of mitogen-activated protein kinase cascade in human myometrial cells. STUDY DESIGN: Confluent cultures of human myometrial cells obtained from ut erine specimens of premenopausal women undergoing hysterectomy were serum s tarved for 48 hours before oxytocin stimulation. Prostacyclin levels, as 6- keto-prostaglandin F-1 alpha, were measured by radioimmunoassay, and the ce llular cyclooxygenase-2 protein content was determined by Western blot. Mit ogen-activated protein kinase activity was assessed by measuring the phosph orylation of myelin basic protein. RESULTS: In a time- and dose-dependent manner oxytocin promoted prostacycli n production in human myometrial cells. Maximal responses were observed aft er 8 hours of stimulation at a dose of 100 nmol/L. This effect was mainly d ue to the expression of cyclooxygenase-2 protein. Within 5 minutes oxytocin significantly stimulated mitogen-activated protein kinase, as compared wit h the expression in untreated controls. The maximal increase in enzyme acti vity (2.5-fold) was obtained at 45 minutes. A selective inhibitor of mitoge n-activated protein kinase activation (PD98059), as well as herbimycin, a t yrosine kinase inhibitor, and the transcriptional blocker actinomycin D, su ppressed oxytocin-induced cyclooxygenase-2 expression and prostacyclin prod uction. The stimulatory action of oxytocin was also sensitive to inhibition by pertussis toxin but appeared to be independent of protein kinase C acti vation. CONCLUSION: Our data indicate a largely unrecognized signal transduction me chanism for oxytocin, involving G-protein-coupled activation of mitogen-act ivated protein kinase and cyclooxygenase-2 gene expression, leading to incr eased prostaglandin production in human myometrial cells. This signaling pa thway complements the rapid activation of the phosphoinositide cycle and ma y be responsible for sustained release of prostaglandins in uterine tissues , promoting labor and parturition.