Hypothalamic-Pituitary-Ovarian Axis

Abstract

The hypothalamic-pituitary system is involved in the control of gonadal development and reproductive rhythmicity (Guillemin, 1967; McCann and Porter, 1969; Frohman, 1973). The gonadotropic hormones, follicle-stimulating hormone and luteinizing hormone, participate in the activation and support of gonadal differentiation and maturation and in the process of hormonal steroidogenesis in the ovaries. Menstrual cyclicity is dependent on the secretion of gonadotropic hormones in adult amounts and sequence. The development of secondary sexual characteristics, as well as the cyclic release of ova, set the stage for conception and implantation. Although the ovaries contain a fund of several hundred thousand follicles at birth, the cyclic release of ova does not commence until about the age of 13 yr. The factors responsible for this latency period are not known. It is related at least in part to the fact that the responsiveness of ovarian tissue to gonadotropins is age dependent and probably mediated by estrogen production by the theca interna (Goldenberg, Recter, and Ross, 1973).