Sympathetic regulation of ovarian functions under chronic estradiol treatment in rats

•Chronic estradiol treatment did not affect ovarian blood flow at rest.•Under estradiol treatment, ovarian estradiol secretion rate was concentrated in narrow ranges.•Estradiol increased the threshold frequency of sympathetic ovarian vasoconstriction.•Estradiol augmented sympathetic inhibition of ovarian estradiol secretion rate.

Activation of the sympathetic nerve to the ovary (superior ovarian nerve: SON) decreases ovarian blood flow and estradiol secretion in rats in the estrous phase. The present study examined the effects of long-term estradiol treatment on the sympathetic regulation of both ovarian blood flow and estradiol secretion. Non-pregnant Wistar rats received sustained subcutaneous estradiol (5 μg/day) or saline for 4 weeks. Chronic estradiol treatment did not affect ovarian blood flow at rest, while changed the basal ovarian estradiol secretion rate, i.e., narrow ranges (4-34 pg/min) in estradiol-treated rats, versus wide ranges (3-192 pg/min) in saline-treated rats of different estrous cycles. SON was electrically stimulated at different frequencies (2, 5 and 20 Hz). Ovarian blood flow was decreased by SON stimulation in a stimulus frequency-dependent manner in both saline- and estradiol-treated rats, but the threshold was shifted from 2 Hz to 5 Hz after chronic estradiol treatment. Ovarian estradiol secretion rate was not significantly changed by SON stimulation at any frequency in saline-treated rats, while it was markedly decreased by SON stimulation at high frequencies (5 and 20 Hz) in estradiol-treated rats. In conclusion, chronic estradiol treatment augments sympathetic inhibition of ovarian estradiol secretion perhaps by inhibiting the hypothalamic-pituitary-ovarian axis.