Testicular estradiol and the pattern of Sertoli cell proliferation in prepuberal bulls

Sertoli cells nourish developing sperm with the number of Sertoli cells being a major determinant of sperm production capacity in a male. The objectives of these studies were to numerically characterize the prepuberal populations of bovine Sertoli cells to determine the pattern of proliferation and to determine if the prepuberal population could be expanded by reducing endogenous testicular estrogens. Groups of Angus-Hereford crossbred bull calves were castrated at 0.25 mo (n = 6) and 1, 2, 3, 4, 5, or 6 mo of age (n = 8 per age). Testes were weighed and equatorial slices fixed. Sertoli cell density was determined following labeling of Sertoli cells with GATA-4 antibody in 30-μm thick sections. The number of Sertoli cells per testis increased linearly from 0.25 mo to 5 mo of age. Sertoli cell numbers appeared to plateau at 5 mo of age with luminal development present at that age. Only a single postnatal wave of Sertoli cell proliferation was detectable in the bull. To evaluate the regulatory role of testicular estrogens, Jersey bull caves were treated twice weekly with the aromatase inhibitor, letrozole, from 2 to 22 wk of age and control animals were treated with the canola oil vehicle. Testes were retrieved at 26 wk of age. Testes were weighed and Sertoli cell density was subsequently determined. Estradiol was lower in testicular tissue from letrozole-treated bulls as expected (P < 0.001). Inhibition of aromatase had no effect on testosterone or circulating LH; testosterone increased with age as expected. Inhibition of aromatase and consequent reduced testicular estradiol did not alter Sertoli cell numbers.