Suppression of the Pituitary Follicle-Stimulating Hormone Secretion during Proestrus and Estrus in Rats by Porcine Follicular Fluid: Possible Site of Action*

These studies were designed to investigate the action of porcine follicular fluid (PFF) on the secretion of FSH and LH in cyclic fen lie rats. PFF was obtained from medium sized follicles and was charcoal treated to remove steroids. Control animals received pig serum (PS). Proestrous rats were injected ip with 1 ml PFF or PS at 1100 or 1800 h, or at both times. Sequential blood collections were obtained at 1300, 1600, and 1900 h proestrus and at 0800, 1100, and 1400 h on estrus. When PFF was injected at 1100 h, plasma FSH levels were significantly depressed on proestrous afternoon but not on estrous morning. In rats treated with PFF at 1800 h, FSH was significantly lower only at 0800 h on estrous morning. When two injections of PFF were given to rats at 1100 and 1800 h, plasma FSH was markedly reduced at 1600 and 1900 h proestrus and at 0800 and 1100 h estrus. In contrast, plasma LH and progesterone in proestrous rats were only altered when two PFF injections were given. All PFF-treated rats ovulated and ...