Inhibition of growth and differentiation of fetal hamster gonads grafted into the adult testis.

A cytomorphological analysis of the effect of adult testes on growth and differentiation of grafted fetal testis or ovaries was performed in hamsters. Fetal gonads, taken at 14 days post-coital age, were grafted for 30 days either under the renal capsule or testicular capsule of scrotal or cryptorchid testes of adult hamsters (weight 115 +/- 23 g). Renal grafts were also performed in males castrated 30 days prior to receiving the fetal gonads. Growth and differentiation of the fetal gonads (testis or ovary) was totally inhibited by the scrotal testis. When the cryptorchid testis was the recipient of fetal gonads, inhibition was correlated inversely with the degree of spermatogenic damage elicited in the cryptorchid testis. No inhibition was observed in fetal gonads grafted under the kidney capsule, nor in castrated, normal or cryptorchid animals. As normal growth and differentiation of both testis and ovary occurred when grafted under the kidney capsule, the inhibitory effect of adult gonads seems to be unrelated to plasma testosterone levels in the host, as levels were undetectable in castrated hamsters and reduced drastically in cryptorchid animals. At the same time, the testicular-inhibiting substance in normal animals did not act at a distance, since its effect was restricted to fetal gonads grafted under the testicular capsule. This inhibitory substance may correspond to the spermatogonial chalone, known to be produced by differentiating spermatogenic cells (mainly spermatocytes and round spermatids in the rat and mouse); these chalones prevent spermatogonial proliferation and, consequently, the critical number of spermatogonia needed to enter meiosis is not attained. It is doubtful if the same substance has the ability to differentiate the fetal ovary or if this effect can be ascribed to a more complex situation involving other testicular peptides of paracrine action and/or locally high levels of androgens.