Cell proliferation and hormonal changes during postnatal development of the testis in the pig

Histometrical evaluation of the testis was performed in 36 Piau pigs from b irth to 16 mo of age to investigate Sertoli cell, Leydig cell, and germ cel l proliferation. In addition, blood samples were taken in seven animals fro m 1 wk of age to adulthood to measure plasma levels of FSH and testosterone . Sertoli cell proliferation in pigs shows two distinct phases. The first o ccurs between birth and 1 mo of age, when the number of Sertoli cells per t estis increases approximately sixfold. The second occurs between 3 and 4 mo of age, or just before puberty, which occurs between 4 to 5 mo of age, whe n Sertoli cells almost double their numbers per testis. The periods of Sert oli cell proliferation were concomitant with high FSH plasma levels and pro minent elongation in the length of seminiferous cord/tubule per testis. Ley dig cell volume increased markedly from birth to 1 mo of age and just befor e puberty. In general, during the first 5 mo after birth, Leydig cell volum e growth showed a similar pattern as that observed for testosterone plasma levels. Also, the proliferation of Leydig cells per testis before puberty s howed a pattern similar to that observed for Sertoli cells. However, Leydig cell number per testis increased up to 16 mo of age. Substantial changes i n Leydig cell size were also observed after the pubertal period. From birth to 4 mo of age, germ cells proliferated continuously, increasing their num ber approximately two- to fourfold at each monthly interval. A dramatic inc rease in germ cells per cross-section of seminiferous tubule was observed f rom 4 to 5 mo of age; their number per tubule cross-section stabilized afte r 8 mo. To our knowledge, this is the first longitudinal study reporting th e pattern of Sertoli cell, germ cell, and Leydig cell proliferative activit y in pigs from birth to adulthood and the first study to correlate these ev ents with plasma levels of FSH and testosterone.