Superior ovarian nerve regulates ovarian estradiol secretion in rats

      It is well known that hypothalamus-pituitary hormones regulate ovarian estradiol secretion. Histological studies in rat have demonstrated that the ovary receives autonomic nerves that reach the ovary via the ovarian nerve plexus (ONP) which is distributed around the ovarian artery, and via the superior ovarian nerves (SON), located in the suspensory ligament. However, it has not yet been clarified whether the autonomic nerves innervating the ovary regulate ovarian estradiol secretion. In the present study, we examined the effects of electrical stimulation of ONP and SON on the ovarian estradiol secretion in rats. Rats were anesthetized on the day of estrous, and ovarian venous blood samples were collected through the catheter inserted into the ovarian vein. Estradiol concentration of ovarian venous plasma was measured using EIA. Evoked volleys were recorded from the ONP and SON. These electrophysiological results suggested both the ONP and SON consist mainly of unmyelinated fibers with only a small percentage being myelinated. Electrical stimulation of ONP at supra-maximal intensity for C-fibers produced decrease in plasma flow rate reaching 74±9%, while no changes in estradiol secretion rate. On the other hand, electrical stimulation of SON at the supra-maximal intensity for C-fibers produced decreases in plasma flow rate reaching 76±3%, and estradiol secretion rate reaching 53±6%. The SON stimulation-induced decreases in plasma flow rate and estradiol secretion rate were blocked by alpha1- and alpha2-adrenoceptor antagonists (prazosin and yohimbine), respectively, but not by beta-adrenoceptor antagonists (propranolol). We conclude that autonomic nerves, which reach the ovary via the SON, have an inhibitory role in ovarian estradiol secretion via activation of alpha2-adrenoceptors.
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