A progesterone binding component in porcine ovarian follicular fluid

Steroid hormone concentrations (progesterone, oestrone, oestradiol-17 beta) in porcine follicular fluids were measured by radioimmunoassay. In confirmation of several previous studies, as follicular maturation proceeded, the concentrations of all three steroids increased, although the relative amounts of the oestrogens decreased compared to progesterone. Analysis of fluids for steroid-binding components was undertaken using ion-exchange chromatography, gel filtration and steroid-binding assays. Evidence is presented in support of a labile binding component which exhibits high affinity and low capacity for progesterone and little or no affinity for oestadiol. Our findings are discussed in relationship to the known retention of progesterone within preovulatory follicles and to previous reports of steroid-binding components in follicular fluids.