• G J Valenzuela, C W Hewitt, and C A Ducsay.
• Department of Obstetrics and Gynecology, San Bernardino County Medical Center, CA 92415-0935, USA.
• Am. J. Obstet. Gynecol. 1995 May 1;172(5):1573-6.

ObjectiveThis study was designed to test the hypothesis that endothelin-1 pretreatment of human myometrium at subcontractile doses in vitro will enhance the contractile response to oxytocin.Study DesignIn vitro contractile oxytocin dose-response curves were generated by use of myometrial strips collected from nonpregnant women (n = 7), pregnant patients at elective cesarean section (n = 7), and patients in active labor (n = 7) in the presence or absence of 10(-9) mol/L endothelin-1. Contractile responses were analyzed by on-line computer, and data were normalized to the maximum response to potassium.ResultsPretreatment with endothelin-1 significantly increased the maximal contractile response of pregnant myometrium (p < 0.01 compared with control). In marked contrast myometrium from nonpregnant patients was unaffected by endothelin-1 pretreatment. Values for the two-point discrimination and Hill coefficient were not different among the treatment groups.ConclusionEndothelin-1 potentiates the oxytocin response of myometrium from pregnant but not nonpregnant women. We speculate that a high circulating level of a uterotonin-like oxytocin may not be necessary to initiate labor. The synergistic interaction between different uterotonins may be sufficient.

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