[Mechanism on onset of secondary sexual characteristics in the female]

Adrenal androgens begin to increase approximately 2 years before the increase in gonadotropin secretion. This contributes to the growth of pubic hair. The development of the breast is primarily under the control of estrogens by the ovary. Reactivation of hypothalamic LHRH pulse generator is the most important in the onset of puberty. This reactivation initially occurs during sleep, followed by sleep-associated LH release and the increase of estradiol during daytime hours. Thereafter, the secretion of gonadotropin and estradiol increases through puberty and the positive action of estradiol on gonadotropin release is established in the middle to late puberty. Recently, growth hormone has been suggested to excert direct ovarian actions and may be involved in onset of secondary sexual characteristics.