Thymic abnormalities induced by castration in aged (NZB X SJL)F1 male mice: distinct effects of early and late castration.

Female but not male (NZB X SJL)F1 (NS) hybrid mice develop thymic abnormalities during aging. To determine the possible participation of androgens in this sex-related difference, we investigated the effect of androgen deprivation, as can be achieved by orchidectomy, on the cellular composition of the thymus of old NS males. Mice were orchidectomized at ages ranging from 3 weeks to 9 months and their thymuses were studied at the ages of 12 or 18 months. Phenotypic characterization of the intrathymic lymphocyte population was carried out using flow cytofluorometry analysis. Orchidectomy performed early in life (3 weeks-3 months) resulted, at 12 months of age, in thymic alterations (expansion of dull Thy-1+ cells, emergence of surface immunoglobulin-bearing cells) resembling those occurring spontaneously in old NS females. In contrast, when orchidectomy was performed later in life (6-9 months), there was a numerical increase of all thymocyte subsets but no major qualitative abnormality at either 12 or 18 months of age. Therefore, the absence of thymic disease in intact NS males may reflect primarily a suppressive effect of androgens that can be reversed by early but not by late orchidectomy.