Pubertal Development in Japanese Boys

Abstract

Testicular enlargement is regarded as the earliest physical sign of the pubertal process in boys. In order to establish the maturational changes of testicular volume in Japanese boys, we measured testicular size of 425 males from birth to adolescence using a transparent plastic ruler. Maturational changes in testicular volume were noted in two periods, during early infancy and adolescence. The testicular volumes during the first three months of life were slightly greater than later in infancy. Thereafter, there was very little increase in testicular volume from the age of 1 to 10 years. After 11 years, there was a sudden increase in size. The mean combined volumes increased from 6.5cm3 at 11 years to 36.7cm3 at 14 years. The largest increment was observed between 13 and 14 years of age and between pubic hair stages I and II. These findings indicate that reaching a testicular volume of 6.5cm3 is a landmark of the earliest stage of puberty in contemporary Japanese boys. In order to correlate changes in testicular volume with those in gonadotropin and testosterone secretion during puberty, we examined also basal and 24-hr secretion of gonadotropin and testosterone in other cross-sectional studies. Basal gonadotropin was found to increase significantly from 10 years of age, and this increment preceded the increase of testicular volume and testosterone secretion. Analysis of 24-hr secretory dynamics of gonadotropin and testosterone concentration suggests that nighttime increase of gonadotropin concentration with initiation of pulsatile secretion, which is believed to be an endocrinological marker for pubertal onset, exists even in the prepubertal stage well before the development of secondary sexual characteristics. Furthermore, the day-night difference with a higher nocturnal level of testosterone indicates the importance of nocturnal testosterone measurement for assessing pubertal development.