Active and passive immunoneutralization of inhibin increases follicle- stimulating hormone levels and ovulation rate in ewes

Abstract

Two experiments were conducted to determine effects of active and passive immunoneutralization of inhibin on FSH secretion and ovulation rate. A synthetic peptide (α-IF) matching the N-terminus of the α-subunit of ovine inhibin was coupled to human α-globulin (hα-G) and used as an immunogen. In experiment 1, estrus was synchronized in 10 sheep that had been actively immunized against α-IF-hα-G or hα-G. Plasma FSH levels were similar in the two groups of ewes at -52 and -48 h (0 h = onset of estrus). In α-IF-hα-G- immunized ewes, FSH increased from -48 to -44 h (18.8-22.1 ng/ml), and then fell to 16.2 ng/ml by 0 h. In hα-G-immunized ewes, FSH decreased from -48 to 0 h (17.6-7.2 ng/ml). Ovulation rate was higher in α-IF-hα-G- than hα-G- immunized ewes (9.4 vs. 2.4). In experiment 2, antibodies (Ab) were extracted from sera obtained from experiment 1 ewes and then were injected i.v. into 12 other ewes. Estrus was synchronized twice during the breeding season using progesterone-releasing pessaries (CIDR-G). One day before CIDR-G withdrawal, α-IF-hα-G and hα-G Ab were administered in a crossover design. After injection of Ab against α-IF-hα-G, plasma FSH increased from 0 to 24 h post-injection (10.9-21.5 ng/ml), after which levels fell to 14.2 ng/ml by onset of the preovulatory LH surge. After injection of Ab against hα-G, FSH levels decreased during the preovulatory period to a low of 8.1 ng/ml. Ovulation rate was higher in α-IF-hα-G- than in hα-G Ab-treated ewes (6.0 vs. 1.8). Active and passive immunoneutralization of inhibin elicited increased FSH secretion during the preovulatory period and increased ovulation rate.