Mechanisms of indomethacin and nimesulide on inhibition of calcium rises in human uterine myocytes

Abstract

Objective: Indomethacin, an inhibitor of cyclooxygenase 1 and 2 (COX-1,2), and nimesulide, a COX-2 selective inhibitor, are both well known inhibitors of prostaglandin (PG) production. It has been assumed that the tocolytic mechanism of nimesulide and indomethacin is only through decreased PG production. The purpose of this study is to test the hypothesis that nimesulide and/or indomethacin have a mechanism of action on human myocytes other than inhibition of PG production. Methods: Human uterine myometrium was obtained from consented patients during cesarean deliveries. Myocytes were cultured, plated, and loaded with the calcium-dependent fluorescent dye, calcium green-1. The relative concentrations of intracellular free calcium were determined by measurement of time-dependent fluorescence changes using a video-fluorimeter. In all experiments, cells were stimulated with 30 μmol/L prostaglandin F2-alpha (PGF 2α). Experiments were performed without pretreatment (control) or with pretreatment with 10 μmol/L indomethacin or 30 μmol/L nimesulide. The percentage of cells demonstrating calcium rises were counted and compared using Fisher’s exact test. A P value of 0.05 was considered significant. Results: After PGF 2α exposure, 33% of cells showed an increase in intracellular calcium. When pretreated with nimesulide, 39% of cells responded to PGF 2α ( P = 0.59). When pretreated with indomethacin, only 16% of cells responded to PGF 2α ( P = 0.019) Conclusions: Pretreatment with nimesulide failed to reduce the fraction of cells that responded to PGF 2α. In contrast, pretreatment with indomethacin significantly reduced the fraction of responding cells. These data suggest that indomethacin exhibits a mechanism of tocolysis other than inhibition of PG synthesis.