Effects of Electrical Stimulation of the Superior Ovarian Nerve and the Ovarian Plexus Nerve on the Ovarian Estradiol Secretion Rate in Rats

Abstract

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...

The role of alpha adrenoceptors in the vascular and estradiol secretory responses to stimulation of the superior ovarian nerve

“…Owing to this blood sampling procedure, changes in ovarian venous estradiol concentration during nerve stimulation would not affect estradiol concentration in systemic arterial plasma. We confirmed the stability of estradiol concentration in systemic arterial plasma between samples collected both at the beginning and at the end of experiment [7]. When the nerve was not stimulated, the ovarian venous plasma flow rate, the ovarian venous estradiol concentration, and the estradiol secretion rate from the ovary were all stable when compared between 5 samples for 35 min [7].…”

“…Our previous study showed that superior ovarian nerve stimulation decreased both plasma flow rate of ovarian venous blood (ovarian blood flow) and ovarian estradiol secretion rate in anesthetized rats [7]. Our present study demonstrated that these two events induced by stimulation of the superior ovarian nerve stimulation were caused by the activation of different alpha adrenoceptors subtypes.…”

“…3). In control experiments without drugs in our previous study [7], electrical stimulation of the superior ovarian nerve resulted in reductions in ovarian venous plasma flow rate, ovarian venous estradiol concentration, and estradiol secretion rate from the ovary, reaching 76 ± 3, 83 ± 6, and 53 ± 6% of prestimulus values, respectively. We will discuss the present In the present study, we observed that blocking alpha 2-adrenoceptors by the i.v.…”

“…All experimental conditions, and techniques for anesthesia, collecting and measuring ovarian venous estradiol secretion rate, and stimulating the superior ovarian nerve, were the same as those previously described [7]. In brief, rats were anesthetized with urethane (initially 1.1 g/kg, i.p.…”

“…In the rat, both sets of fibers terminate in dense perivascular plexus around arteries, but those from the superior ovarian nerve terminate abutting on steroidogenic interstitial cells [6]. Stimulation of the extrinsic nerves to the ovary reduces blood flow through the ovary, while stimulation of the superior ovarian nerve, but not of the ovarian nerve plexus, is known to reduce estrogen output [7].…”