Hormonal control of follicle growth

During the follicular phase, the ovarian follicle (preantral follicle) grows by pronounced proliferation of granulosa cells. During the second half of the follicular phase, the follicle accumulates fluid, which leads to formation of an antrum (antral follicle). 

Hormonal and physiological changes during the menstrual cycle. BBT, Basal body temperature. 

The latter mechanism is believed to involve the formation of catecholestrogen (2-hydroxyestradiol) after uptake by the median eminence, which, because of its abundance, competes with hypothalamic norepinephrine for inactivation by catechol-O-methyltransferase (COMT). This inactivation results in a higher norepinephrine content in the median eminence, which favors GnRH release. 

The large bolus of LH released (preovulatory LH surge) in response to positive feedback by estradiol induces ovulation in about 1 day, probably by stimulation of production of granulosa plasminogen activator, which leads to formation of plasmin, an enzyme that may be responsible for the digestion of the basal lamina and, consequently, for the rupture of the follicle (ovulation). 

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