SIZE, NUMBER, CELLULAR PROLIFERATION, AND ATRESIA OF GONADOTROPIN-INDUCED FOLLICLES IN EWES

To determine the effect of exogenous gonadotropin on size, number, cel lular 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, re spectively; 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 ad ditional group of ewes (Day 13 control) received no treatment and were slaughtered on Day 13. All ewes received an i.v. injection of bromode oxyuridine (BrdU, a thymidine analog; 5 mg/kg(-1) BW) 1 h before slaug hter. For both ovaries from each ewe, number and surface diameter of a ll visible follicles were recorded, and antral follicles were classifi ed as small (less than or equal to 3 mm), medium (> 3 mm to less than or equal to 6 mm), or large (> 6 mm). To evaluate rate of proliferatio n of follicular cells, ovaries were fixed by perfusion with Carnoy's s olution, and BrdU was immunolocalized in paraffin-embedded sections by use of a specific primary antibody and indirect immunoperoxidase dete ction. As, an index of the rate of cellular proliferation, labeling in dex (LI: number of BrdU-labeled nuclei expressed as a percentage of to tal nuclei) of granulosa and thecal cells was determined by image anal ysis of antral follicles of known diameter. Follicular status (atretic vs. nonatretic) also was evaluated morphologically by using the histo logical sections. After 24 h of treatment (i.e., on Day 14), FSH-P-tre ated ewes had an increased (p < 0.01) number of medium follicles compa red with vehicle-treated ewes. After 48 and 72 h of treatment (i.e., o n Days 15 and 16), FSH-P-treated ewes had more (P < 0.01) medium and l arge follicles than vehicle-treated ewes. In addition, on Day 16, FSH- P-treated ewes had fewer (P < 0.01) small follicles than vehicle-treat ed ewes. Overall, granulosa cell LI was greater (p < 0.01) than thecal cell LI. In addition, across all groups, granulosa cell LI decreased (P < 0.01) as follicular size increased, whereas thecal cell Ii was si milar for small and medium follicles but decreased (P < 0.05) for larg e follicles. Across all follicular size classes, granulosa cell LI was greater (P < 0.01) for FSH-P-treated ewes than for vehicle-treated ew es after 24 h of treatment (Day 14), but not after 48 or 72 h of treat ment (Day 15 or 16). Across all days and size classes of follicles, in cidence of atresia was less (p < 0.01) for: FSH-P-treated than for veh icle-treated ewes. Thus, FSH-P treatment decreased the incidence of at resia and induced recruitment and growth of ovine follicles as evidenc ed by 1) the increased number of medium and large antral follicles, 2) the increased LI of follicles after 24 h of FSH-P administration, and 3) the decreased incidence of atresia on Days 14 to 16.