what switches estrogen from positive to negative feedback?
As well as playing a secondary role in follicular responsiveness to FSH, LH is the trigger for ovulation itself. In response to the switch in estrogen mediated feedback from negative to positive, the LH mid-cycle surge is created. This activates a whole cascade of inflammatory responses in the dominant follicle leading to the breakdown of the follicular boundary wall and the escape of the oocyte with its cumulus oophorus.