Effects of various steroids on the thymus, spleen, ventral prostate and seminal vesicles in old orchidectomized rats

Abstract

ABSTRACT The effects of several steroids on the regenerating thymus in ageing male rats have been studied. Rats aged from 12 to 15 months were orchidectomized and 7 days later implanted s.c. with silicone elastomer tubing containing 25 mg testosterone, 5α-dihydrotestosterone (DHT), oestradiol, progesterone or corticosterone. One group of rats received an empty implant. Thirty days later the rats were killed and the thymus, spleen, ventral prostate and seminal vesicles weighed and retained for histology. Whole blood was taken for total and differential white cell counts; plasma was prepared for radioimmunoassay of testosterone, oestradiol, progesterone and corticosterone. After orchidectomy only, a multilobular thymus was present, and histologically the tissue appeared healthy. In testosterone- and oestradiol-treated rats, thymus weight was reduced to about 50% of that in untreated animals. Histologically, much of the thymus taken at autopsy was fat and what remained was poorly organized and contained a much lower density of thymocytes. The total white cell count was significantly reduced in these animals, the effect appearing to be predominantly on lymphocytes. Although treatment with DHT also resulted in a lower mean thymus weight than that of orchidectomized animals, histologically the tissue appeared similar to that of the untreated castrated animals. In rats treated with DHT, the total white cell count was significantly higher than in testosterone-implanted rats. Both progesterone and corticosterone implants resulted in significantly smaller mean thymus weights, although these steroids were not as potent as testosterone or oestradiol. Corticosterone, but not progesterone, appeared to cause a significant reduction in circulating lymphocytes. Dihydrotestosterone possessed only half the potency of testosterone in restoring the weights of the accessory sex organs. Serum concentrations of testosterone in orchidectomized old rats were 0·33 ± 0·02 nmol/l and in testosterone-implanted rats 4·8 ± 0·4 nmol/l. These results raise the possibility that testosterone and oestradiol may have caused atrophy of the thymus, while DHT may have retarded regeneration of the thymus without any atrophic effect. It remains to be seen whether the different responses between testosterone and DHT, in both the thymus and accessory sex organs, are due to differences in intrinsic action or differences in the metabolism of the steroids. J. Endocr. (1987) 113, 51–55