From menarche to regular menstruation: endocrinological background.

Marked changes in hormone secretion occur from childhood to adulthood. Prior to puberty gonadotropin-releasing hormone (GnRH) secretion is markedly suppressed. At the onset of puberty, the hypothalamic gonadostat is derepressed and the amplitude of GnRH pulses increases. Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) levels increase gradually during puberty stimulating follicle maturation and estrogen production in the ovaries. Only the negative feedback mechanism is powerful before puberty, while the positive feedback mechanism becomes active for the first time in late puberty. As a result, normal cyclicity is usually established at that time. During normal menstrual cycle, steroidal and nonsteroidal hormones mediate the effect of the ovaries on the hypothalamic-pituitary system. Estradiol and progesterone are important regulators of FSH and LH secretion, while inhibins play a role in the control of FSH secretion. Gonadotropin surge attenuating factor (GnSAF) is a nonsteroidal ovarian substance that controls the amplitude of the midcycle LH surge by antagonizing the sensitizing effect of estradiol on the pituitary.