Inhibitor effect of omeprazole in isolated human myometrial smooth muscle

The aim of the present study was to investigate the effect of omeprazole, a n H+-K+-ATPase inhibitor, in myometrial smooth muscle strips from women und ergoing elective caesarean section at term. Isolated myometrial strips take n with informed consent were obtained from eight pregnant women undergoing elective caesarean section at term (not in labour) and mounted in organ bat hs for recording of isometric tension. We recorded the effect of increasing concentrations of omeprazole on spontaneous and Ca2+-induced contractions of myometrial smooth muscle and on contractions of myometrial smooth muscle pretreated with indomethacin (3x10(-6) M) and L-NAME (3 x 10(-5) M). Omepr azole (10(-4)-10(-3) M) decreased the amplitude and frequency of spontaneou s contractions in a time- and concentration-dependent manner in all myometr ial smooth muscle isolated from pregnant women. The decrease in amplitude o f contractions in myometrial smooth muscle reached statistical significance beginning from the concentration of 3 x 10(-4) M, Addition of indomethacin (3 x 10(-6) M) and L-NAME (3x10(-5) M) in to the organ baths 30 min before did not change relaxation responses to omeprazole. When 8 mM Ca2+-precontr acted in Ca2+-free medium myometrial smooth muscle were exposed to increasi ng concentrations of omeprazole (10(-5)-10(-3) M), omeprazole produced rela xation responses in a time- and concentration-dependent manner, reaching st atistical significance at 10(-4) M. These results show: (1) omeprazole time - and concentration-dependently decreased spontaneous contractile activity in myometrial smooth muscle isolated from pregnant women, (2) omeprazole-in duced relaxations was not influenced by indomethacin and NG-nitro-L-arginin e methyl ester (L-NAME), suggesting that it is not mediated by cyclooxygena se products and nitric oxide, and (3) omeprazole brought about time- and co ncentration-dependently relaxation of myometrial smooth muscle precontracte d by 8 mM Ca2+ in Ca2+-free medium. This effect of omeprazole may be due to blockade of the calcium channels. (C) 2001 Elsevier Science Inc. All right s reserved.