The source of ovarian oestradiol and androstenedione in the sheep during the luteal phase.

The secretion of oestradiol and androstenedione was investigated in sheep by cannulating both ovarian veins in situ. The mean ovarian blood flow (ml/min +/- SE) was significantly higher on the side containing the corpus luteum (7.67 +/- 1.36) than on the contralateral side (4.93 +/- 0.85). The mean secretion (ng/min +/- SE) of oestradiol (1.09 +/- 0.36) and androstenedione (1.52 +/- 0.16) was higher on the side containing at least one large follicle (diameter greater than 4 mm) than on the contralateral side (0.19 +/- 0.05 and 0.62 +/- 0.21, respectively). The secretion of oestradiol was unchanged following enucleation of the corpus luteum but fell to very low levels (0.062 +/- 0.022 ng/min) after enucleation of follicles diameter greater than 4 mm. The secretion of androstenedione fell significantly after enucleation of both corpus luteum and largefollicles. These results suggest that during the luteal phase in the sheep oestradiol is secreted virtually exclusively by the largest non-atretic Graafian follicle. Androstenedione in contrast arises from both follicle, corpus luteum and possibly stroma.