Thymus and the endocrine system: ovarian dysgenesis in neonatally thymectomized rats

By 10 days after neonatal thymectomy, the areas of lymphocytic depletion were being repopulated by plasma or reticular cells. Subsequently, ovarian dysgenesis was observed in 50-day-old thymectomized female rats as hyperplasia of ovarian interstitial cells an an enhanced degeneration of follicles. Thymectomized rats at 130 and 170 days of age showed complete ovarian dysgenesis, testicular atrophy, hypertrophy of pituitary beta-cells with pronounced cytoplasmic haloes, and lymphocytic infiltration in the pituitary, thyroid and prostate glands. These results suggest that neonatal thymectomy may initially influence the lymphoid organs (i.e. the immune system) and that changes in the immune system may result in the autoimmune-like damage in the endocrine organs and the prostate gland. Associated with these changes, the concentrations of plasma progesterone and 17 alpha-hydroxyprogesterone were significantly reduced in 130-day-old thymectomized female rats with respect to the sham-thymectomized controls. The concentration of plasma oestradiol-17 beta in thymectomized female rats was the same as in sham-thymectomized female rats. These results suggest that gestagens may normally suppress immune responses but that, in the case of thymectomized female rats, the reduced levels of gestagens may lead to enhanced immune responses.