Inhibition of uterine contractility with various tocolytics with and without progesterone: in vitro studies.

OBJECTIVE

Various tocolytics are used to suppress uterine contractility in patients in preterm labor. Progesterone (P4) is used in patients at high risk for preterm delivery. In this study, we evaluated the effects of various tocolytics with and without P4 to examine effects on uterine contractility.

STUDY

DESIGN

Uterine tissues (n = 280) from women undergoing cesarean at term were exposed in vitro to various agents (vehicle, magnesium sulfate [MgSO(4)], nifedipine, indomethacin, or pinacidil-all with and without P4). Contractility was measured before and after addition of the various agents.

RESULTS

P4 alone at 10(-5) mol/L concentration has little effect to inhibit contractility (P ≥ .05). MgSO(4) (2-8 × 10(-3) mol/L) inhibits uterine contractility (P < .05) but there is no change when combined with P4 (P > .05). Nifedipine (10(-8) mol/L) and indomethacin (10(-5) mol/L) inhibit contractions alone (P < .05) and to a greater extent when combined with P4 (P < .05). P4 significantly (P < .05) reduced the effects of pinacidil (10(-6.5) mol/L).

CONCLUSION

Combinations of P4 with nifedipine or indomethacin, but not MgSO(4), might be used to effectively suppress preterm labor.