Involvement of melatonin in the inhibition of gonadotropin secretion by stress and its mechanism

(1)褪黑素抑制促性腺激素分泌的部位。脑室注射褪黑素抑制纳洛酮诱导的LH释放，但不抑制NMDA或LHRH诱导的LH释放。结果表明，在下丘脑LHRH神经网络中，褪黑素的作用部位位于阿片作用部位的下游和兴奋性氨基酸作用部位的上游。(2)各种应激对纳洛酮诱导的LH释放的影响急性制动应激或感染应激显著抑制纳洛酮诱导的LH释放，禁食3 d中度抑制，禁食24 h或足电击应激不影响纳洛酮诱导的LH释放。(3)各种应激后LH抑制与松果体褪黑激素释放的相关性在上述各种应激大鼠中，纳洛酮诱导的LH释放抑制程度与血浆褪黑激素浓度之间无明显相关性。(4)松果体参与纳洛酮的抑制 ...更多信息 在急性束缚应激后，松果体切除部分恢复了纳洛酮诱导的LH释放，表明松果体的作用。而在其他应激状态下，去松果体对大鼠的应激反应无明显影响。(5)感染应激抑制促性腺激素分泌的部位。静脉注射LPS可抑制纳洛酮和NMDA诱导的LH释放，但对LHRH诱导的LH释放无影响。结果表明，在下丘脑LHRH神经网络中，LPS的作用部位位于阿片和兴奋性氨基酸作用部位的下游。LPS注射后，第三脑室后腹侧部室管膜细胞（tanycells）c-fos表达增强。(6)其他因素：脑室内注射IL-1β并不抑制纳洛酮、NMDA或LHRH诱导的LH释放，这表明非IL-1β介导的机制至少部分涉及感染应激、急性制动和褪黑激素对促性腺激素分泌的抑制。少

(1) The site where melatonin inhibits gonadotropin secretion.Intraventricular injection of melatonin inhibited naloxone-induced, but not NMDA- or LHRH- induced, LH release. The results showed that the site of melatonin action is located downstream to the site of opioid action and upstream to that of exciatory amino acid action in the hypothalamic LHRH neural network.(2) Effects of various kinds of stress on naloxone-induced LH release.Naloxone-induced LH release was significantly inhibited by acute immobilization stress or infectious stress, moderately inhibited by 3-day fasting , and not affected by 24-hour fasting or footshock stress.(3) Correlation between LH suppression and pineal melatonin release after various kinds of stress.No significant correlation was found between the degree of inhibition of nalloxone-induced LH release and plasma melatonin concentration in rats undergoing various kinds of stress described above.(4) Involvement of the pineal in the inhibition of naloxone-in … More duced LH release by various kinds of stress.Pinealectomy partially restored naloxone-induced LH release after acute immobilization stress, indicating a role of the pineal gland. No obvious effect of pinealectomy was found in rats with other kinds of stress.(5) The site where infections stress inhibits gonadotropin secretion.Intravenous injection of LPS inhibited naloxone-induced and NMDA-induced, but not LHRH-induced, LH release. The results showed that the site of LPS action is located downstream to the sites of action of opioid and excitatory amino acid in the hypothalamic LHRH neural network. Intense c-fos expression was found in ependymal cells (tanycytes) of the posteroventral portion of the third ventricle after the LPS injection.(6) Other factors.Intraventricular injection of IL-1β did not inhibit naloxone-, NMDA- or LHRH- induced LH release, suggesting that mechanism(s) not mediated by IL-1β is, at least in part, involved in inhibition of gonadotropin secretion by infectious stress, acute immobilization and melatonin. Less