SUPPRESSION OF PITUITARY SECRETION OF FOLLICLE-STIMULATING-HORMONE BY PORCINE FOLLICULAR-FLUID DURING PRO-ESTROUS AND ESTRUS IN THE RAT - EFFECTS ON GONADOTROPIN AND STEROID-SECRETION, FOLLICULAR DEVELOPMENT AND OVULATION DURING THE FOLLOWING CYCLE

Adult, 4-day-cyclic rats were injected with PFF [porcine follicular fluid] or pig serum at various hours of pro-estrus and estrus. Plasma FSH [follicle stimulating hormone] levels were suppressed following PFF treatment at any time of pro-estrus and estrus. This suppression was always followed by a rebound increase in plasma FSH. In contrast, plasma LH [luteinizing hormone] concentrations were unaffected by PFF treatment and neither gonadotropin was altered by treatment with pig serum. When rats treated with PFF or pig serum were allowed to complete 1 additional cycle, plasma LH and FSH concentrations at the pro-estrus and estrus after treatment were not significantly different among groups regardless of treatment or time of treatment. All ovaries of rats treated with PFF or pig serum on the next pro-estrus morning before ovulation were histologically similar. All animals ovulated a normal complement of ova at the next estrus regardless of whether preovulatory, secondary or both increases of plasma FSH had been blocked by PFF treatment during the previous cycle. In animals given PFF during the preceding cycle, plasma estradiol and progesterone concentrations were significantly altered on the morning and afternoon of pro-estrus respectively. Increased plasma FSH concentrations at pro-estrus and estrus may not be essential for folliculogenesis and ovulation in the subsequent cycle. Alternatively, the rebound of FSH on day 1 of diestrus after the suppression of both phases of FSH secretion at pro-estrus and estrus may be sufficient to provide ovulatory follicles for the next pro-estrous day.