ENDOTHELIN-1 POTENTIATES THE IN-VITRO CONTRACTILE RESPONSE OF PREGNANT HUMAN MYOMETRIUM TO OXYTOCIN

OBJECTIVE: This study was designed to test the hypothesis that endothe lin-1 pretreatment of human myometrium at subcontractile doses in vitr o will enhance the contractile response to oxytocin. STUDY DESIGN: In vitro contractile oxytocin dose-response curves were generated by use of myometrial strips collected from nonpregnant women (n = 7), pregnan t patients at elective cesarean section (n = 7), and pateints in activ e 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 w ere normalized to the maximum response to potassium. RESULTS: Pretreat ment 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 an d Hill coefficient were not different among the treatment groups. CONC LUSION: Endothelin-1 potentiates the oxytocin response of myometrium f rom pregnant but not nonpregnant women. We speculate that a high circu lating level of a uterotonin-like oxytocin may not be necessary to ini tiate labor. The synergistic interaction between different uterotonins may be sufficient.