Seasonal changes in testicular structure and function and the effects of gonadotropins in the freshwater turtle,Chrysemys picta

Plasma testosterone was measured at stages during the reproductive cycle of control male turtles (Chrysemys picta) and following hypophysectomy and/or mammalian FSH or LH injection. Testosterone levels were highest in April and December when large Leydig cells were observed in the interstitium but the epithelium was inactive. During active spermatogenesis (July, October) plasma steroid levels were basal, and not significantly reduced by hypophysectomy. While LH injections had no effect, FSH was a potent stimulus to plasma testosterone in both intact and hypophysectomized turtles. Histologic observations during the testicular cycle and after hypophysectomy indicated that the tubular epithelium was dependent on endogenous pituitary hormone secretion but the interstitium did not atrophy during the experimental period. Injections of FSH in May increased testicular weight and caused disappearance of vacuoles and granules from apical portions of the Sertoli cell with a consequent reduction in cell height. Neither FSH nor LH had obvious effects on the morphology of the interstitium in control or hypophysectomized turtles either in July or November.