Effect of scrotal insulation on the pituitary-testicular axis of the ram.

The testes of rams were insulated for 28 days. After 28 days typical degenerative changes occurred in the tubular compartment of the testis. Spermatozoa, spermatids and, in many tubules, spermatocytes were absent. A pronounced dilatation of the testicular lymph vessels was noted, and a morphometric study indicated that the volume fraction occupied by Leydig cells was greater than in controls. A serial bleeding regimen showed that peripheral plasma concentrations of FSH were elevated and of testosterone were usually reduced after scrotal insulation. Although mean testosterone levels were unchanged after 7 days of treatment, there were more hormone episodes, each of significantly reduced amplitude. LH values were elevated at this time and there was an increase in the number and amplitude of LH episodes. After 14 days of scrotal insulation, mean and basal levels of testosterone were significantly reduced, and episodes of secretion were much smaller in amplitude. Mean LH values were elevated and each secretory episode was of significantly greater amplitude than in control blood. These results show that the testes of scrotally insulated rams are relatively insensitive to endogenous LH and that this treatment affects cells within the seminiferous tubule and those in the interstitial compartment.