The isoflavone daidzein is a commonly found phytoestrogen in soybean meal, a staple of most swine diets. Estrogens have been found to decrease ovarian follicle atresia, thus potentially increasing ovulation rate. The objective of this study was to determine if daidzein affects follicular cell apoptosis, the underlying mechanism for atresia. Cultured primary porcine granulosa cells were plated on 8-well polylysine-coated microscope slides (Nunc, Naperville, IL; n=3 independent populations of granulosa cells per slide). Cells were treated for 48 h with daidzein or estradiol at 0.1, 1, and 10 µM, or EtOH vehicle control in serum-free media, and subsequently processed using an in situ apoptosis assay kit (Oncor, Gaithersburg, MD). Degree of apoptosis was quantified microscopically (9 measurements/treatment/slide from a preplanned grid) using an image analysis system (Optimas 5.2, Redmond, WA), and means separated using contrast analysis. Daidzein treatment decreased (P<0.05) mean apoptosis (% area) from 61.6% in the controls to 27.6% in the phytoestrogen-treated cells. Estradiol treatment combined was not different from controls; however percent apoptosis had a tendency to be lower (P=0.06) at 10 µM estradiol (24.4) . In addition, daidzein tended to decrease (P=0.1) percent apoptosis vs. estradiol (45.8). These results indicate that daidzein has the ability to decrease follicular cell atresia. This inhibition appears to be more substantial than that of estradiol. Increased use of daidzein in the swine diets could lead to more follicle recruitment and ovulations, thus potentially increasing litter size. Supported by the Illinois Council on Food and Agricultural Research and the Illinois Soybean Program Operating Board.
Copyright, 1998 (Property of Authors and the Society for the Study of Reproduction)
