Ovulation in mammals is controlled by two hormones secreted by the Pituitary Gland, the Follicle Stimulating Hormone (FSH), and the Luteinizing Hormone (LH). FSH, which is secreted by the anterior lobe of the pituitary is responsible for the increase in the production of estrogenic hormone (estrone)* which stimulates Graafian follicles (ovarian follicles) to mature and ovulate. LH, on the other hand, organizes the corpus luteum** upon ovulation and causes the secretion of progesterone which stimulates the secretion of viscid glycogenic fluid for the nutrition of the embryo prior to the development of the vascular system. The mechanisms of these hormonal interaction and their effects on the estrous cycle in mammals operate in the principle of reciprocal action.
A parallel situation exists in lower vertebrates. In fishes, gonadal activities such as the transition from juveniles to sexual maturity and the seasonal spawning cycle are pre-determined by Gonadotropin secreted by the Meso-adenohypophysis lobe of the pituitary.