FSH influences follicle viability, oestradiol biosynthesis and ovulation rate in Romney ewes

in Reproduction

Summary. Injection of steroid-free bovine follicular fluid (bFF; 2 × 5 ml s.c. 12h apart) into anoestrous ewes lowered plasma FSH concentrations by 70% and after 24 h had significantly (P < 0·01) reduced the number of non-atretic follicles (≥ 1 mm diam.) without influencing the total number of follicles (≥ 1 mm diam.) compared to untreated controls. Hourly injections of FSH (10 μg i.v. NIH-FSH-S12) for 24 h did not influence the number of non-atretic follicles but did negate the inhibitory effects of bFF on follicular viability. Hourly injections of FSH (50 μg i.v., NIH-FSH-S12) + bFF treatment for 24 h significantly increased the total number of non-atretic follicles, and particularly the number of medium to large non-atretic follicles (≥ 3 mm diam.) compared to the untreated controls (both P < 0·01). The 10μg FSH regimen (without bFF) significantly increased aromatase activity in granulosa cells from large ( ≥ 5 mm diam.; P < 0·01) but not medium (3–4·5 mm diam.) or small (1–2·5 mm diam.) follicles compared to controls. The 10 μg FSH + bFF regimen had no effect on granulosa-cell aromatase activity compared to the controls. However, the 50 μg FSH plus bFF regimen increased the aromatase activity of granulosa cells from large, medium and small non-atretic follicles 2·6-, 8·3- and ≥ 11-fold respectively compared to that in the control cells.

Ewes (N = 11) that ovulated 2 follicles had significantly higher plasma FSH concentrations from 48 to 24 h and 24 to 0 h before the onset of a cloprostenol-induced follicular phase (both P < 0·01) than in the ewes (N = 12) that subsequently ovulated one follicle. Hourly FSH treatment (1·6 μg i.v., NIAMDD-FSH-S15) for 24 h but not for any 6 h intervals between 48 and 24 h or 24 and 0 h before a cloprostenol-induced luteolysis also resulted in significant increases (P < 0·05) in the number of ewes with 2 ovulations.

We conclude that (1) the number of non-atretic antral follicles in sheep ovaries is influenced by plasma FSH concentrations; (2) the level of follicular oestradiol biosynthesis can be enhanced by FSH treatment; and (3) sustained elevations of plasma FSH concentrations for 24 h but not 6 h within 48 h of the onset of luteolysis significantly enhances the ovulation rate in Romney ewes.

If the inline PDF is not rendering correctly, you can download the PDF file here.

 

     An official journal of

    Society for Reproduction and Fertility