The effect of prostaglandin f2alpha on endocrine parameters in early pregnancy.

The luteolytic effect of prostaglandin f2alpha (PGF2alpha) has been well documented in a variety of primates. This property has not been proven in early human pregnancy. A study of the luteolytic activity of extraamnial administration of 5 mg PGF2alpha was carried out on 7 healthy women who were less than 6 weeks pregnant and on 4 women who were more than 9 weeks pregnant. Serum levels of 17beta-estradiol, 17-hydroxyprogesterone, progesterone and human chorionic gonadotropin (HCG) were measured by radioimmunoassay before, during and after the administration of PGF2alpha. Abortion was successfully induced in all the patients with early pregnancies, but in the control group of more mature pregnancies only one of the four women aborted. In the older pregnancies, the administration of 5 mg PGF2alpha caused no significant alteration in the serum levels of the measured hormones. In the younger pregnancies the serum concentration of 17beta-estradiol and progesterone decreased within hours after PGF2alpha administration. Serum 17-hydroxyprogesterone concentrations remained unchanged at a high level and declined significantly later in a manner similar to HCG. This discrepancy in the decline of 17-hydroxyprogesterone as opposed to progesterone and 17beta-estradiol may be explained by two mechanisms, the one mechanical, and the other secondary luteolytic. The marked increase of intrauterine pressure occurring within minutes after PGF2alpha instillation damages the fetoplacental unit. This leads to a decrease in the placental steroido-genesis and HCG production necessary for the maintenance of the corpus luteum.