Follicular Morphology Oocyte Diameter and Localization of Fibroblast Growth Factors in the Domestic Dog Ovary

摘要

Remarkably little is known about folliculogenesis in the dog. Objectives were to characterize (1) changes in follicle/oocyte diameter and granulosa cell number and (2) expression of Fibroblast Growth Factor -2 (FGF-2) and -7 (FGF-7) during ovarian follicle development in this species. Fourteen ovarian pairs were excised and processed for histological evaluation. Two to four serial sections/bitch were stained with hematoxylin, and follicle/oocyte diameters and granulosa cell number were determined at each developmental stage. Means follicle and oocyte size were compared among stages by ANOVA. Relationships between follicle diameter and oocyte size and granulosa cell number were determined using correlation and regression analysis, respectively. Another eight serial ovarian sections/bitch were processed for immuno-staining to determine FGF-2 and -7 expression. Primordial and primary follicles were similar in size (P < 0.05), but smaller than the progressively increasing (P < 0.05) diameters of later stage counterparts. Oocyte diameter gradually increased (P < 0.05) among oocytes derived from primordial, primary, secondary and early antral follicles with no difference (P > 0.05) thereafter. Oocyte size and granulosa cell number increased (P < 0.01) with follicular diameter. Except during anestrus, FGF-2 was detectable in oocytes and granulosa cells of primordial to secondary follicles. In adult bitches, FGF-7 was localized in granulosa cells of primary and secondary follicles and also occurred in the theca layer of antral follicles during proestrus and estrus. In summary, folliculogenesis in the domestic dog occurs in two phases with a preantral phase characterized by increasing follicle size in association with oocyte growth and granulosa cell proliferation. The subsequent antral phase is linked with marked granulosa cell proliferation and accumulation of antral cavity fluid. Finally, the temporal expression pattern of FGF-2 implies its role in follicular activation, whereas FGF-7 activities appear related to later folliculogenesis.