PITUITARY AND OVARIAN-FUNCTION IN EWES IMMUNIZED AGAINST THE AMINO-TERMINAL PEPTIDE (ALPHA-N) OF THE INHIBIN ALPHA(43)-SUBUNIT

Immunization of ewes against the amino-terminal peptide (alpha N) of t he pro-alpha-subunit of inhibin has been shown to reduce fertility, th ought to be due to disruption of ovulation. The aims of this study wer e to examine the effects of active immunization of ewes against alpha N on circulating concentrations of FSH, LH and on ovarian inhibin and progesterone, and to relate these observations to number of corpora lu tea and oocyte recovery rates. Ewes were immunized against one or both of two recombinant full length bovine-alpha N immunogens (FP, and FP2 ). Three experiments were performed in which jugular venous plasma was sampled from control and immunized ewes: (1) hourly across the oestro us surge of gonadotrophins (Expt 1); (2) daily for one entire oestrous cycle, and in the subsequent cycle, oviducts were flushed to recover ovulated eggs (Expt 2); and (3) samples were taken at I0 min intervals greater (P < 0.05) in immunized groups than in controls for all exper iments. The number of eggs per corpus luteum recovered from the oviduc ts was lower (P < 0.05) in the alpha N-immunized groups (39%) than in controls (88%). There were more (P < 0.05) corpora lutea per ewe in FP 2 immunized groups 4 (1.8 +/- 0.45) and 5 (1.75 +/- 0.5) than in the c ontrol group (1.13 +/- 0.13), but no increase in group 3 (FP1; 1.4 +/- 0.24). The oestrous surge of LH, basal values across cycle and the fr equency of LH pulses were similar in treated and control groups. Circu lating FSH concentrations were higher (P < 0.05) than those of control s in all immunized groups that had binding greater than 10% at all sta ges of the cycle, except during the oestrous surge. A corresponding de crease (P < 0.05) in circulating inhibin concentrations was observed i n most immunized groups, with a significant negative correlation betwe en inhibin values and alpha N-binding in the follicular phase of the c ycle. The pattern of progesterone production during the cycle was simi lar, with a slight nonsignificant increase in immunized compared with control ewes. These data confirm the previous observation that ovulati on is impaired in ewes immunized against the aminoterminal peptide of inhibin alpha(43) and also suggest that the mechanism of this effect d oes not involve disruption of pituitary function, implying a role for alpha N in the intraovarian events of ovulation.