Size, number, cellular proliferation, and atresia of gonadotropin-induced follicles in ewes.

To determine the effect of exogenous gonadotropin on size, number, cellular proliferation, and atresia of follicles, ewes (n = 3-5/treatment/day) received an injection of vehicle or FSH-P (a pituitary extract) twice daily on Days 13, 14, and 15 (5, 4, and 3 mg FSH-P/injection, respectively; Day 0 = estrus) and were slaughtered on Days 14, 15, or 16 (i.e., after 24, 48, or 72 h of FSH-P treatment, respectively). An additional group of ewes (Day 13 control) received no treatment and were slaughtered on Day 13. All ewes received an i.v. injection of bromodeoxyuridine (BrdU, a thymidine analog; 5 mg/kg-1 BW) 1 h before slaughter. For both ovaries from each ewe, number and surface diameter of all visible follicles were recorded, and antral follicles were classified as small (< or = 3 mm), medium (> 3 mm to < or = 6 mm), or large (> 6 mm). To evaluate rate of proliferation of follicular cells, ovaries were fixed by perfusion with Carnoy's solution, and BrdU was immunolocalized in paraffin-embedded sections by use of a specific primary antibody and indirect immunoperoxidase detection. As an index of the rate of cellular proliferation, labeling index (LI: number of BrdU-labeled nuclei expressed as a percentage of total nuclei) of granulosa and thecal cells was determined by image analysis of antral follicles of known diameter. Follicular status (atretic vs. nonatretic) also was evaluated morphologically by using the histological sections. After 24 h of treatment (i.e., on Day 14), FSH-P-treated ewes had an increased (p < 0.01) number of medium follicles compared with vehicle-treated ewes.(ABSTRACT TRUNCATED AT 250 WORDS)