Contractile effects of endothelin 1 and endothelin 3 on myometrium and small intramyometrial arteries of pregnant women at term.

This in vitro study was undertaken to investigate the effects of endothelin 1 (ET-1) and endothelin 3 (ET-3) on intramyometrial arteries and myometrial tissue of the uterus from pregnant women at term. Segments of small myometrial arteries (outer diameter 100-500 microns) obtained at cesarean section were isolated and mounted in tissue chambers. The effect of ET-1 and ET-3 on isometric tension was compared with the action of noradrenaline. In similar experiments on myometrial strips, the effect of ET-1 and ET-3 was studied in comparison with oxytocin. ET-1 and ET-3 both produced contractions of arteries and myometrial strips, ET-1 being the most potent. The response of ET-1 was more powerful than the effect of the reference compounds, i.e. noradrenaline with regard to myometrial arteries and oxytocin with regard to the myometrium. It is concluded that endothelins are powerful constrictors of myometrial arteries from pregnant women and possess strong oxytocic effects. In particular, ET-1 could be involved in the regulation of myometrial contractility and/or uteroplacental blood flow.