Responsiveness of intraovarian dog follicles in vitro to epidermal growth factor and vascular endothelial growth factor depends on ovarian donor age.

We investigated the influence of epidermal growth factor (EGF) and vascular endothelial growth factor (VEGF) on in vitro follicle development within ovarian cortices recovered from pre-pubertal (≤6 months) versus peri-pubertal dogs (≥10 months). Ovarian cortices were cultured for 3 or 7 days in EGF (0 or 10 ng/ml) and VEGF (0, 0.1 or 1 ng/ml) and subjected to histological and apoptosis analyses. Fresh cortices from the same dogs served as "non-cultured controls" (NCC) and were evaluated similarly. The response of ovarian follicles to growth factors differed between pre-pubertal versus peri-pubertal tissues. For pre-pubertal dogs, percentage of structurally normal follicles in cortices cultured for 3 days in low VEGF (0.1 ng/ml) and EGF alone was comparable to that of the NCC. Follicle density declined in all cultured groups even after 3 days. Primary follicle diameter in all cortices cultured for 7 days, except in low VEGF, was smaller than that of the NCC, and percentage apoptotic follicles sharply increased in all treatment groups compared to the NCC. For peri-pubertal donors, percentages of structurally normal follicles decreased in all culture treatments at 3 and 7 days of incubation compared to the NCC. However, more normal follicles were found in cortices cultured in low VEGF and the two VEGF and EGF combinations than in the absence of growth factors or with EGF alone. Culture reduced the density of developing follicles, but follicle diameter was similar to that of the NCC. TUNEL analysis revealed that high-VEGF (1 ng/ml) treatment protected follicles against apoptosis, with the proportion of apoptotic follicles at Day 7 being comparable to that of the NCC. The findings demonstrate that the response of ovarian cortices to growth factor supplementation varied between pre-pubertal versus peri-pubertal donors.