The effects of short-term genistein exposure on ovarian folliculogenesis in immature rats were examined stereologically. To determine whether genistein acts as an estrogen agonist or antagonist, the results were compared with the effects of 17α-ethynylestradiol. Immature female rats received 50 mg/kg/bw of genistein in dimethyl sulfoxide subcutaneously daily for three consecutive days from 18 to 20 days. The second group was injected with 1 μg/kg/bw of 17α-ethynylestradiol in olive oil in the same schedule. Each group had a corresponding control. Genistein increased ovary and ovarian stroma volumes by 18.50% (P < 0.05) and 53.40% (P < 0.05), respectively, and changed the parenchyma to stroma ratio in favor of stroma. Genistein induced decreases in the number of primordial (by 17.23%; P < 0.05), primary (16.62%; P < 0.05), and secondary follicles (12.29%: P < 0.05), whereas the number of atretic secondary follicles increased (5.10-fold; P < 0.05). The number of healthy large follicles was raised by 27.3% (P < 0.05), accompanied by 35.64% more atretic large follicles (P < 0.05). Similarly to genistein, estradiol changed the parenchyma to stroma ratio in favor of stroma, and reduced the number of primordial follicles, but the number of primary follicles was elevated. There were more healthy and atretic small and large follicles. In conclusion, genistein acted as an estrogen antagonist and had an inhibitory effect on the initial phase of folliculogenesis. In the other phases, genistein acted as an estrogen agonist, stimulating transition from the preantral to antral stage of folliculogenesis, and altering the ratio of follicular parenchyma and ovarian stroma in favor of stroma.
Copyright © 2012 Wiley Periodicals, Inc.