Influences of the gonad on the thymus in the mouse

Summary

In mice of an inbred Japanese dd-strain, age changes in the thymus weight were studied for both sexes from 5 days until 300 days of age. Further studies were made on effects of gonadectomy on the thymus in both male and female mice which were gonadectomized at 35 days and 100 days of age.

• 1. The thymus grows markedly at the same rate in both sexes in early life until at about 35 days it reaches a maximum in weight. Then it decreases in weight due to age involution. During adolescence and early maturity until about 100 days the decrease in thymus weight is relatively rapid, and it is more prominent in males than in females. During sexual maturity after 120 days until 300 days so far examined, the decrease in the thymus weight is very slow, and the thymus is significantly heavier in females than in males.

• 2. The sex difference in the thymus weight is no longer evident in gonadectomized mice. The thymus of the male responds to castration by a remarkable increase in weight, while the thymus of the female is little influenced by ovariectomy. From these considerations it is surmised that the sex difference in the thymus weight is due to that the thymus in the male is suppressed by the testis, namely, the male gonadal hormone.