Preovulatory follicle development and luteal function in ewes immunized against a synthetic peptide sequence of the alpha subunit of bovine inhibin.

Abstract

Immunization against inhibin consistently results in an increase in ovulation rate in sheep, but the effects that this treatment has on follicle development are unknown. In order to determine the influence of inhibin, parameters of follicle development were assessed in ewes that had been actively immunized against a synthetic peptide homologous to the N-terminal sequence (alpha 1-29, Tyr30) of the alpha subunit of bovine inhibin, a treatment that neutralizes the biological activity of endogenous inhibin. The final stages of preovulatory follicle development that culminate in ovulation were induced in seasonally anoestrous ewes, and follicles were recovered prior to the predicted time of ovulation. After priming with progestagen, inhibin-immunized and control ewes were treated with gonadotrophin-releasing hormone (GnRH) by continuous infusion (200 ng/h). The ovaries were recovered at slaughter 24 h after the start of GnRH treatment and all follicles greater than or equal to 2.0 mm diameter were dissected out and their capacity to produce oestradiol in vitro was assessed. Further groups of similarly treated animals were blood-sampled daily to determine luteal function following GnRH-induced ovulation. The ovaries were recovered from these ewes at slaughter 10 days after the start of GnRH treatment, the corpora lutea were dissected out and their progesterone content was assessed. There were more (P less than 0.01) follicles of 5-6 mm diameter (3.2 +/- 0.45 (S.E.M.) compared with 1.1 +/- 0.25 follicles/ewe) and more (P less than 0.001) follicles of greater than 6 mm diameter (2.8 +/- 0.56 compared with 0.9 +/- 0.17 follicles/ewe) in inhibin-immunized than in control ewes.(ABSTRACT TRUNCATED AT 250 WORDS)