EXPERIMENTAL STUDY ON THE PROLIFERATION AND THE MATURATION OF GERM-CELL, SERTOLI CELL AND LEYDIG CELL OF THE RAT TESTIS

Kinetics of the proliferation and the maturation of germ cell, Sertoli cell and Leydig cell of the rat testis, with special reference to the influences of gonadotropic hormones, was investigated by the auto-radiographic method of intratesticular injection of tritiated thymidine in the following experimental conditions; (1) normal rat (Wistar) group reared from birth to maturation (2) immature rat group administered with gonadotropic hormones (FSH-NIH, LH-NIH, HCG, PMS): (3) adolescent rat group administered with gonadotropic hormones: (4) hypophysectomized mature rat group.<br>(a) Germ cell<br>The gonocyte proliferates by mitosis and differentiates to the spermatogonium A and B, successively 10 days and 12 days after birth. The seminiferous tubule in 50 percent contains spermatogonium which has incorporated tritiated thymidine. This percentage remains unchanged throughout the period of the testicular maturation. Differentiation of the spermatogonium to the primary spermatocyte by meiosis begins on the 14th day after birth. The number of the seminiferous tubules which contain the primary spermatocytes with intranuclear incorporation of tritiated thymidine shows a transient increase, but from the 25th day decreases again gradually to the figure of 5 percent which remains also unchanged throughout the maturation period. During differentiation of the primary spermatocyte to the secondary spermatocyte, and to spermatid and spermatozoa, incorporation of tritiated thymidine in these cells is autoradiographi-cally not demonstrated. This indicates that DNA synthesis in the nucleus of the germ cell takes place in the process of differentiation of gonocyte to the spermatogonium and the primary spermatocyte, but not after the differentiation of the secondary spermatocyte to the spermatozoa.<br>Any one of gonadotropic hormones does not stimulate the process of the proliferation from the gonocyte to the spermatogonium and the primary spermatocyte, whereas the process of the differentiation from the primary spermatocyte to the secondary spermatocyte and the maturation of spermatid to the spermatozoa is promoted mainly by follicle stimulating hormone (FSH). Luteinizing hormone (LH) alone does not show this action, but the possibility of the synergism with FSH can not be denied.<br>(b) Sertoli cell<br>DNA-synthesis in the nucleus of Sertoli cell can be observed in the new-born rat testis, with increasing activity to the 8th day after birth. But with gradual decrease after 13th day tritiated thymidine incorporated Sertoli cell can not be demonstrated in any seminiferous tubule. Gonadotropic hormones have not any influences on the process of cellular proliferation.<br>(c) Leydig cell<br>Leydig cell shows the intranuclear incorperation of tritiated thymidine at birth in about 10 percent. But this figure decreases gradually down to 2-3 percent at the maturation, which remains equal throughout the reproductive age. This result can be thought to indicate that in the mature rat testis Leydig cell is being constantly replaced at a rate of 2-3 percent. Proliferation and maturation of Leydig cell is stimulated by luteinizing hormone, but the finding that human chorionic gonadotropin (HCG) reveals more effectiveness than pure luteinizing hormone in the process of proliferation may indicate the possibility of synergistic action of luteinizing hormone and follicle stimulating hormone.