According to the text, the secretion of gonadotropins (LH and FSH) stimulates follicular development during the follicular phase. During the luteal phase, the corpus luteum secretes large amounts of progesterone. High levels of progesterone (and estrogen) exert negative feedback on the pituitary, leading to low levels of FSH and LH. Since FSH (Follicle Stimulating Hormone) is required for follicle growth, its low concentration prevents the development of new follicles during this phase .