A Preliminary Assessment of the Source of Oestrogen Within the Ovary of the Domestic Fowl, Gallus Domesticus

Oestradiol was measured by radioimmunoassay in blood draining individual preovulatory follicles and in different ovarian tissues of the hen. The concentration of oestradiol in blood from follicles 20 to 50 hr before ovulation ranged from 66 to 264 pg/ml and was less than that in peripheral blood collected concurrently, suggesting a net uptake rather than secretion of oestradiol by the follicle at these times. In one bird approximately 6 hr before ovulation, the highest content of oestradiol in tissue (35 ng) was in the small (less than 5 mm) follicles and ovarian stroma; this represented 87.5% of the total ovarian content. Only 0.86 to 1.02 ng oestradiol (2.0 to 2.5) was found in the large preovulatory follicles and 2.22 ng (5.5%) in the postovulatory follicles. High concentrations of oestradiol (2.4 ng/g) were also found in the liver. These results suggest that the small follicles and/or ovarian stroma are the main site of oestradiol production in the fowl; they do not exclude the possibility that oestradiol is secreted at a high rate by the mature follicle for a short period immediately before ovulation, thus influencing the release of LH.