Shortening increases spontaneous contractility in myometrium from pregnant women at term.

Objective The purpose of this study was to determine whether shortening alters spontaneous contractility in myometrial strips that are obtained from pregnant women. Study design Isometric contractions were measured in myometrial strips that were obtained at cesarean delivery from 14 pregnant women at term. After 2 hours of stretching, the strip lengths were decreased by 4%, 6%, or 8%. Spontaneous contractility was measured for 120 minutes with or without prostaglandin synthase inhibitor indomethacin (10 −5 mol/L), and the cumulative concentration response to oxytocin was determined. Results Contractility was increased by 29% and 34% in strips that shortened by 4% and 6%, respectively. Preincubation with indomethacin increased contractility by 15% in stretched strips and decreased contractility by 30% and 19% in 4% and 6% strips, respectively. Contraction frequency was increased by 26% and 53% for the strips that were shortened to 6% and 8%, respectively. These increases were prevented by indomethacin. The oxytocin responses were similar at all lengths. Conclusion Shortening of myometrial strips from pregnant women at term increases spontaneous contractility by a mechanism that apparently involves prostaglandins.