Introduction

The testis is an active organ as early as the 7th week of gestation (for review cf. Faiman, Winter & Reyes, 1981). After a period of low activity during the second part of intrauterine life, the hypothalamic-hypophyseal-gonadal axis is reactivated shortly after birth (Winter & Faiman, 1972; Forest, Cathiard & Bertrand, 1973). After a short, postnatal period with high serum levels of gonadotropins and testosterone, hormone production in the testis decreases and remains low until puberty. Thus, the testis plays an important endocrine role many years before puberty. It is the scope of the present paper to review aspects of early testicular maturation as well as the relationship between the endocrine activity of the testis, initiation of sperm production, and growth and development of the body.

The neonatal period

During the first 3 months of life an increase in serum levels of luteinizing hormone (LH) and follicle stimulating hormone (FSH) occurs (Winter & Faiman, 1972). This is accompanied by a rise in serum testosterone to a mean of approximately 200 ng/100 ml (Forest et al, 1973) a level which is in the range of the adult male. After the age of 3 months serum levels of LH, FSH, and testosterone fall to prepubertal values (serum testosterone less than 6 ng/100 ml). Recently, it has been demonstrated that this reactivation of the hypothalamic-hypophyseal-gonadal axis is associated with an increase and subsequent decrease of testicular size (Cassorla et al, 1981; Siebert, 1982). The increased endocrine activity also seems to affect the development of the germ cells and Sertoli cells during the neonatal period.