Vasotocin analogues which competitively inhibit vasopressin stimulated uterine activity in healthy women

Summary. Three analogues of posterior pituitary hormones, 1 - deamino - 2 - D - Tyr(OEt) - 4 - Val - 8 - Om - vasotocin(dE - VVT), l-deamino-2-D-Tyr(OEt)-4-Thr-8-Orn-vasotocin(dE-TVT) and 1-deamino-2-D-Tyr(OEt)-oxytocin(dE-OXY) were compared for their inhibitory effects on vasopressin (VP)-induced uterine activity in healthy women. At menstruation, during recording of intrauterine pressure (18 recording sessions in 11 women), intravenous infusion of lysine vasopressin (LVP, 1 ng/min/kg/body weight) induced an increase of the uterine activity and dysmenorrhoea-like symptoms. Intravenous injections of all analogues (10 μg/kg body weight) caused relief of symptoms and inhibition of uterine activity, dE-TVT was the most effective and dE-OXY was least active. With dE-TVT almost complete inhibition of contractions was seen during the first 10 min after injection. The duration of effect was also greatest with that analogue (40–50 min). Only dE-OXY had an agonist effect on spontaneous uterine activity. Pharmacokinetic studies of intravenous dE-TVT (10 ng/kg body weight) showed that the plasma half-life was approximately 16 min and the clearance 30 1/h. The bioavailability of 100 ng/kg given intra-nasally was about 5·5%. Further studies are recommended.