Interaction of vasopressin and prostaglandin on myometrial activity in vivo in the first trimester of human pregnancy.

The interaction of vasopressin (VP) and prostaglandin (PG) F2 alpha on myometrial activity was studied by intrauterine pressure recording in 40 women due to undergo therapeutic abortion in the first trimester. In a control group the uterine activity did not change during eight hours of recording without drug administration. In a second group, who had intravenous injections of 8-lysine vasopressin (LVP, 0.1-0.5 IU), it was found that 0.3 IU was the smallest dose that consistently gave an effect on myometrial activity, and that repeated injections gave responses of practically the same magnitude. In the remaining women in the study, LVP injections, 0.3 IU, were given before, during and two hours after an intravenous infusion of PGF2 alpha at 4 or 20 micrograms/minute. Although there were great individual variations, potentiation and enhancement of the LVP effect were the most common reactions, especially with the lower dose of PG. An interaction of PG and other endogenous myometrial stimulants such as VP might be important in the aetiology of spontaneous abortion and the combination of PG with VP-like substances might be of value in therapeutic abortion during the first trimester.