ABSTRACT
The production of an ovum in the alternate ovaries of a woman, month by month, is controlled by the cyclic release of two gonad-stimulating glycoproteins from the anterior pituitary gland: FSH (follicle stimulating hor mone) and LH (luteinizing hormone). The release of these two gonadotrophic hormones is regulated by GnRH (gonadotrophin release hormone), a decapeptide.
GnRH is secreted by cells in the arcuate nucleus of the hypothalamus, in the floor of the third ventricle. The cells secrete for 6 minutes in unison, under the influence of a local neuronal oscillator discharging at hourly inter vals. The circ-horal (every 60 minutes) pulses of GnRH are transported in the portal hypothalamico-hypophyseal venules, down the pituitary stalk to the capillaries of the anterior pituitary gland. The rising concentration of GnRH in the portal blood stimulates the basophilic pituitary gonadotrophs to release FSH. Then, with some overlap at midcycle, LH is also secreted for 14 days into the general circulation (Figures la and b). The half-life of FSH is 3 hours; that of LH is 1 hour.
