Rapid compensatory hypertrophy of the lamb testis after neonatal hemiorchidectomy: endocrine and light microscopical...

The testis mass of lambs hemiorchidectomized (HO) within 1 week of birth exceeded that of control testes by 23%, 67%, and 114% at 4, 8, and 12 weeks; the epididymis was 39% heavier than control epididymides by 12 weeks. The seminiferous tubular mass in HO testes grew at a faster rate than in control testes to achieve full compensation by about 10 weeks; Sertoli cell division was augmented in the 1- to 4 week phase and Sertoli cell cytoplasm increased throughout. The major growth response of the interstitium of HO testes occurred in the 1- to 4 week period but did not obtain full compensation by 12 weeks; the vascular component responded to HO by rapid growth in the 8- to 12 week period. There was a low incidence of division amongst gonocytes (prespermatogonia) in both groups of lambs but at 12 weeks spermatogonial mitoses, spermatocytes, and tubular lumina were present in four out of four HO tests but only one of three control testes. In the same lambs, HO induced an immediate increase in circulating plasma concentrations of FSH to 3-4 x control values at 8 weeks, which were then suppressed to near control values by 10 weeks. Apart from transient increases in LH (at 4-5 weeks) and testosterone (6-7 weeks) above control values, there were no differences between HO and control lambs in the circulating concentrations of any other hormone measured (LH, GH, TSH, PRL, and testosterone). The evidence suggests that the major prepubertal influence on testicular development and growth in lambs is the FSH-provoked response of the Sertoli cells.