Abstract:The present experiments examined the effects of electrical stimulation of the superior ovarian nerve (SON) and the ovarian plexus nerve (OPN) on the ovarian estradiol secretion in rats. The rats were anesthetized on the day of estrus, and the ovarian venous blood was collected intermittently. The secretion rate of estradiol from the ovary was calculated from differences in the estradiol concentration between ovarian venous plasma and systemic arterial blood plasma, and from the flow rate of ovarian venous plasma. Either an SON or OPN, ipsilateral to the ovary from which ovarian venous blood was collected, was electrically stimulated at a supramaximal intensity for C-fibers. The secretion rate of estradiol was significantly decreased by 47 ± 6% during SON stimulation, but it was not significantly changed during OPN stimulation. These results suggest that autonomic nerves, which reach the ovary via the SON, have an inhibitory role in ovarian estradiol secretion.Key words: superior ovarian nerve, ovarian plexus nerve, estradiol, secretion, rat.Many studies have examined the relationship between hypothalamic-pituitary-ovarian hormones and ovarian functions. However, although several histological studies have described the innervation of vagal parasympathetic and sympathetic nerves including both afferents and efferents to the ovary, the roles of these autonomic nerves in ovarian function have not been sufficiently clarified [1][2][3][4][5][6]. Histological studies by Burden et al. [1,7] demonstrated that autonomic nerves enter the ovary via hilar perivascular plexuses, and tiny branches from these plexuses extend into the contiguous steroidogenic interstitial gland cells. Autonomic nerves to the rat ovary reach the organ by two routes: the ovarian plexus nerve (OPN) along the ovarian artery and the superior ovarian nerve (SON) in the suspensory ligament [8,9]. We recently demonstrated that electrical stimulation of the splanchnic nerve or the OPN produces a vasoconstriction of ovarian arterioles and a reduction of ovarian blood flow in rats [10,11]. This result suggests a vasoconstrictor role of ovarian autonomic nerves in regulating ovarian blood flow. On the other hand, earlier studies demonstrated that a denervation of the OPN [12] or the SON [13] alters estradiol secretion from the ovary. These results suggest that ovarian autonomic nerves regulate ovarian estradiol secretion. However, no reports have directly examined the effect of stimulation of the autonomic nerves innervating the ovary on ovarian estradiol secretion. In the present study, we aimed to clarify the effects of electrical stimulation of the SON and the OPN on the secretion rate of estradiol from the ovary in rats.Previously, our laboratory developed methods for measuring the secretion rates of catecholamines from the adrenal medulla [14,15] and thyroid hormones from the thyroid gland [16] in rats. In the present study, we applied these methods to the measurement of the secretion rate of estradiol from the ovary. Although some previous r...