Effects of thymectomy on the endocrine glands of the rat.

The effects of thymectomy on the thyroid gland, the adrenal cortex, the testes and the lymph nodes of the rat follow the same pattern as those observed in guinea pigs but in a very attenuated form. Thymectomized rats do not show the wasting observed in thymectomized guinea pigs. The effects on the adenohypophysis are approximately the same in rats and guinea pigs, but the sequence of the changes is different. Injections of thymic extract or of presumably pure thymic hormone suppressed all the effects of thymectomy on the endocrine glands of the rat. In rats, thymic hormone was found in the thymus, the lymph nodes and the spleen. It disappeared from the lymph nodes and the spleen within three days of thymectomy and did not reappear, although most of the changes in the endocrine glands were transitory. The implications of the observations for understanding the consequences of thymectomy are discussed.