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.