Influence of the thymus on steroidogenesis by rat ovarian cells in vitro.

Thymic hormones and factors have been shown to modulate the function of other endocrine glands including the gonads. Absence of the thymus during development results in ovarian dysgenesis characterized by a decrease in the number of follicles and corpora lutea, bringing about severe changes in reproductive function. To examine whether thymic secretions might affect ovarian activity, whole dispersed ovarian cells obtained from immature rats pretreated with pregnant mare serum gonadotrophin were exposed to a thymus fraction of approximately 28 kDa and also to the media from incubated thymuses (TIM) and the conditioned media from cultured thymic reticuloepithelial cells (TCM). The thymic fraction caused a dose-dependent decrease in human chorionic gonadotrophin (hCG)-stimulated production of progesterone, oestradiol and testosterone, but had no effect on their synthesis in the absence of hCG. Similarly, hCG-induced production of these steroids was decreased by TIM and TCM. Progesterone secretion was the most markedly affected. These results suggest: (1) that the thymus contains a factor with a molecular weight of approximately 28 kDa which interacts with hCG in ovarian cells, (2) that the thymus can release active substances which modify steroid secretion by the ovary in vitro and (3) that the reticuloepithelial cells of the thymus are involved in the secretion of factors which modulate the stimulation by hCG of steroidogenesis in ovarian cells.

Growth control of experimental tumor by syngeneic thymocyte extracts.

The effect of cell-free extracts obtained from thymocytes of 8, 18 and 23 day fibrosarcoma-bearing U rats and normal U rats on tumor growth was investigated. The results show that thymocyte extracts of 8 day tumor-bearing rats inhibit the tumor growth in implanted animals and no significant effect was found with extracts from other times, or from normal thymocytes. Some of the inhibitory activity was lost by dialysis, which led us to assume that low molecular weight substances are involved in the antitumor immune response.