EFFECT OF HYPOPHYSECTOMY, SEX OF HOST, AND OR NUMBER OF TRANSPLANTED TESTES ON SERTOLI-CELL NUMBER AND TESTICULAR SIZE OF SYNGENEIC TESTICULAR GRAFTS IN FISCHER RATS/

One or more neonatal testicular grafts were transplanted for 60-65 day s into young adult inbred Fischer rats to determine the effect of hypo physectomy, sex of host, and/or the number of transplanted testes on t esticular size and Sertoli cell number. All host rats had been castrat ed or ovariectomized and some were hypophysectomized as well, Al the e nd of the treatment, testes were fixed and embedded in Epon before his tologic sections (0.5 mu m or 20 mu m) were evaluated by stereology. T esticular grafts placed in castrated adult male rats with intact pitui taries weighed more (p < 0.01) and had more (p < 0.01) Sertoli cells t han those placed in hypophysectomized hosts. Testicular grafts that we re recovered from hypophysectomized rats 34 days posttransplantation a nd placed in pituitary-intact males for 30 days had larger (p < 0.05) parenchymal weights and more Sertoli cells than did testes re-transpla nted into hypophysectomized rats, However, this delayed period of Sert oli cell proliferation did not extend to 65 days of hypophysectomy. Wh en two or four testes were transplanted into castrated males or ovarie ctomized female hosts for 65 days, there was no difference in the graf t weights or Sertoli cell numbers between sexes, Four transplanted tes tes per rat produced more (p < 0.01) total testicular parenchyma and a greater (p < 0.01) number of Sertoli cells per testis than did two te stes regardless of sex of the host. This model has shown that the peri od of Sertoli cell proliferation can be delayed by hypophysectomy, tha t Sertoli cell number can be influenced by endogenous hormones, and th at a major component in regulation of testicular size is at the level of the testis in this model. Hence, this model should facilitate study of experimental endocrine manipulation control and potential experime ntal intervention to increase Sertoli cell number and testicular size.