Serum Steroids and Pituitary Hormones in Infants with Particular Reference to Testicular Activity

We have determined the concentrations of pregnenolone, progesterone, 17-hydroxyprogesterone, androstenedione, dehydroepiandrosterone, testosterone, 5α-dihydrotestosterone, and androsterone in serum collected from 34 boys and 11 girls between 5–40 weeks of age, and we have compared these data with the concentrations of FSH, LH, and PRL in the same samples. Clear sex differences in the serum concentrations of testosterone and 5α-dihydrotestosterone were found to exist between 5–25 weeks of age, and during this period the serum concentrations of these steroids in the male infant population are similar to those in the lower normal adult male range. This sex difference is indicative of a high level of testicular steroidogenesis, which was also supported by the higher serum concentrations of 17- hydroxyprogesterone in boys compared to girls, between 10-25 weeks of age, and the good correlation between serum concentrations of 17-hydroxyprogesterone and testosterone in these boys. High serum concentrations of 5a-dihydrotestosterone in boys between 5-25 weeks of age also suggest a high level of 5α-reductase activity at this age. There were no sex differences in serum concentrations of the other steroids measured, but it was observed that concentrations of steroids of direct or indirect adrenal origin, i.e. pregnenolone, dehydroepiandrosterone, androstenedione, and androsterone, were generally highest in the youngest subjects and correlated well with each other. Unlike 5α-dihydrotestosterone, serum androsterone concentrations did not correlate with those of testosterone in boys, indicating that its origin is more closely linked to adrenal androgen production. High concentrations of serum FSH were found in girls compared to boys, while the corresponding concentrations of LH were higher in boys below 20 weeks of age compared to girls of a similar age. There was no sex difference in the serum concentrations of PRL and, although the concentrations of PRL were generally highest in infants below 10 weeks of age, no significant correlations were found to exist between serum PRL and steroids of adrenal origin. However, good correlations were found to exist among testosterone, 5α-dihydrotestosterone, and the gonadotropins in the male infant population, which supports the hypothesis that testosterone and/or 5a-dihydrotestosterone may play a role in the development of a very sensitive negative feedback control of pituitary gonadotropin secretion during infancy in boys.