Serum concentrations of follicle stimulating hormone and luteinizing hormone in normal girls and boys during prepuberty and at early puberty.

Serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) morning levels were determined in 327 normal prepubertal and early pubertal children of both sexes, utilizing a highly sensitive and specific microparticle enzyme immunoassay. Female (F) and male (M) prepubertal (Tanner's stage I) subjects were divided into 4 age groups: less than 3 months (F1, M1), 3 to 12 months (F2, M2) 12 to 24 months (F3, M3) and older than 24 months (F4 and M4). F pubertal subjects were classified in Tanner's stage breast II (F5) and III F6), while M pubertal subjects belonged to Tanner's stage genitalia II (M5). Serum LH levels were relatively low in prepubertal girls and showed a significant increment in group F6. By contrast, serum LH levels were relatively high in M1 and M2, decreased to levels similar to F in M3 and M4, and increased again at puberty in M5. Serum FSH levels were relatively high in girls of all prepubertal groups, even though they decrease significantly in M4. An increase was detected in pubertal group M6. All M prepubertal groups had significantly lower FSH levels than F prepubertal groups. The high serum LH of boys during the first year of life is probably a consequence of an activation of the hypothalamic GnRH pulse generator that is not apparent in girls. On the other hand, the high serum FSH of prepubertal girls is probably a consequence of a weak restraint influence of the prepubertal ovary on pituitary FSH secretion. This sexual dimorphism in gonadotropin secretion regulates, in a sex-specific fashion, prepubertal gonadal function in the two sexes.