The fetal membranes as a possible source of progesterone in the amniotic and allantoic fluids of pregnant sheep

Abstract

To assess the possible source of progesterone in the fetal fluids of pregnant sheep, we measured the changes in progesterone concentrations in amniotic fluid (AF) and allantoic fluid (ALF) during pregnancy and compared these values with those in the maternal and fetal circulations. In acute experiments, the concentration of progesterone in ALF was greater than that in AF, and in both compartments, progesterone rose progressively between day 50 of pregnancy and term (day 145). In contrast, in maternal peripheral and uterine venous blood as well as in umbilical cord blood the mean concentration of progesterone increased until day 130, but fell at term. Similar results were obtained in chronically catheterized sheep during late pregnancy. The pattern of progesterone change in the AF and ALF suggested that the steroid might originate from a different source than progesterone in the vascular compartments. By means of in vitro incubation studies, we showed that the chorioallantoic membrane and amnion from sheep at term pregnancy had the capacity to convert [3H]pregnenolone to [3H]progesterone. These results raise the possibility that there may be local changes in steroid hormone concentrations within the tissues and fluids of the pregnant uterus. These changes could be of importance in altering the intrauterine endocrine milieu at the time of birth.