EFFECT OF PASSIVE-IMMUNIZATION AGAINST INHIBIN ON FSH-SECRETION, FOLLICULOGENESIS AND OVULATION RATE DURING THE FOLLICULAR PHASE OF THE ESTROUS-CYCLE IN MARES

Physiological roles of inhibin in mates were investigated by means of passive immunization using an antiserum to inhibin that had been raise d in a castrated goat. Eight mares were given an intravenous injection of either 100 mL (n=4) or 200 mL (n=4) of inhibin antiserum 4 d after a single intramuscular injection of PGF2alpha on Day 8 after ovulatio n, 4 control mares were treated with 100 mt castrated goat serum in th e same manner. Jugular vein blood samples were collected after treatme nt with the serum until 192 h post treatment. Follicular growth and ov ulations were monitored by ultrasound examination at 24-h intervals. T he ability of the inhibin antiserum to neutralize the bioactivity of e quine inhibin was examined in vitro using a rat pituitary cell culture system. Suppression of secretion of FSH from cultured rat pituitary c ells by equine follicular fluid was reversed by the addition of increa sing doses of the inhibin antiserum, thereby indicating its bioactivit y. Plasma levels of FSH and estradiol-17 beta were higher in mares tre ated with the inhibin antiserum. The ovulation rate was significantly higher in mates treated with antiserum (100 mL = 3.75 +/- 0.63; 200 mL = 4.50 +/- 0.65) than in control mares (1.25 +/- 0.25). These results demonstrate that inhibin is important in regulating FSH secretion and folliculogenesis in mares. They also show that neutralization of the bioactivity of inhibin may become a new method for the control of foll iculogenesis and ovulation rate in mates. (C) 1998 by Elsevier Science Inc.