Sertoli Cell Proliferation during Prepubertal Development in the Rhesus Monkey (Macaca mulatta) Is Maximal during Infancy when Gonadotropin Secretion Is Robust

Although a marked pubertal increase in Sertoli cell number is a hallmark of testicular development in the rhesus monkey, the ontogeny of this somatic cell type before puberty is less clear. To clarify this issue, groups (n = 4) of neonate (1–2 d old), infant (4–5 months old), juvenile (14–17 months old), and adult male rhesus monkeys were injected with 5-bromo-2′-deoxyuridine (BrdU) 2 h before castration. Tissue was fixed in Bouin’s fluid, and the percentage of BrdU-labeled Sertoli cells at each developmental stage was calculated. In addition to the labeling index, Sertoli cell number per testis for the neonate and infant groups was enumerated using standard histomorphometry and compared with that previously reported by this laboratory for juvenile and adult rhesus monkeys. The number of Sertoli cells per testis in infants (156 ± 49 × 106, mean ± sd) was 4-fold greater than that in neonates (42 ± 12 × 106). The previously established value for this parameter in juvenile monkeys was 286 ± 121 × 106. Incorporation of BrdU into nuclei of Sertoli cells indicated that these cells were mitotically active at all three stages of prepubertal development. The labeling index in the neonate and infant groups (1.33% in both cases), however, was significantly greater than that in juveniles (0.25%). From the foregoing results, we conclude that Sertoli cell proliferation during prepubertal development in the rhesus monkey occurs predominantly during infancy, when gonadotropin secretion is elevated, and to a lesser extent during the juvenile phase of development, when circulating gonadotropin concentrations are undetectable.