Uterine blood flow and myometrial activity at menstruation, and the action of vasopressin and a synthetic antagonist.

Local endometrial blood flow was measured by a thermistor technique and myometrial activity by intrauterine pressure recording in 10 women before and during menstruation. The effect of lysine vasopressin infusion (1 pmol/kg body-weight per min) and of bolus injection of a synthetic oxytocin analogue, 1-deamino-2-D-Tyr(OEt)-4-Thr-8-Orn-oxytocin (10 nmol/kg body-weight), were studied. Spontaneous variations in blood flow were seen synchronous with clearly demarcated uterine contractions, the myometrial activity being significantly increased in early (day -1 to day +2) compared with late (day +3 to day +5) menstrual phase. The vasopressin infusion decreased blood flow, stimulated uterine activity and caused slight to moderate dysmenorrhoea-like pain. These effects were completely inhibited by the injection of the oxytocin analogue. In-vitro studies on uterine arteries confirmed that the analogue also inhibited the vasopressin-induced constriction of the uterine arteries. This antagonist was more effective than two other analogues, 1-deamino-2-D-Tyr(OEt)-4-Val-8-Orn-oxytocin and 1-deamino-2-Tyr(OEt)-oxytocin. The counteracting effect of 1-deamino-2-D-Tyr(OEt)-4-Thr-8-Orn-oxytocin on the vasopressin-induced decrease of blood flow and increase of contractions supports the therapeutic value of the drug in primary dysmenorrhoea and preterm labour.