Changes in Free Progesterone in the Serum, Peritoneal Fluid and Follicular Fluid through the Menstrual Cycle and Pregnancy

Abstract

Progesterone is said to play an important role in the secretory transformation of the endometrium, maintenance of gestation and relaxation of the myometrium. Progesterone is also said to be involved in ovulation and fertilization, and is contained in large amounts in the follicular fluid and peritoneal fluid. As with other steroid hormones, progesterone exists in the blood in proteinbound and free forms, and it is the free form which exhibits biological activity. In order to evaluate the biological activity of progesterone, we determined the percent free progesterone, employing the method used by Vlahos et al. for the determination of testosterone. No significant difference was noted between the percent free progesterone in the follicular phase (4.44±0.30%) and luteal phase (4.77±0.26%) of the menstrual cycle. However, a tendency for the percent free progesterone to rise was recognized in the first, and the value significantly increased to 5.54±0.51% in the third trimester (p<0.005).
The percent free progesterone during the follicular phase in the peritoneal fluid was 4.95±0.30%, and in the follicular fluid, 5.39±0.22%, both values being larger than the value in the serum during the same phase.