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。脑室内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，褪黑素作用位点位于阿片作用位点的下游，兴奋性氨基酸作用位点的上游。(2)不同应激对纳洛酮诱导的LH释放的影响。急性固定应激或感染性应激显著抑制纳洛酮诱导的LH释放，3 d禁食有中度抑制，24小时禁食和足部休克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无显著相关性。(4)不同应激条件下，松果体参与抑制纳洛酮诱导的LH释放。松果体切除术部分恢复了急性固定应激后纳洛酮诱导的LH释放，表明松果体的作用。对其他应激大鼠，松果体切除术无明显影响。(5)感染应激抑制促性腺激素分泌的部位。静脉注射LPS抑制纳洛酮诱导和nmda诱导的LH释放，但不抑制lhrh诱导的LH释放。结果表明，LPS作用位点位于下丘脑LHRH神经网络中阿片和兴奋性氨基酸作用位点的下游。注射LPS后，第三脑室后腹部室管膜细胞（伸长细胞）中可见高强度的c-fos表达。(6)其他因素。脑室内注射IL-1β不抑制纳洛酮、NMDA或LHRH诱导的LH释放，表明非IL-1β介导的机制至少部分参与了感染应激、急性固定和褪黑素抑制促性腺激素分泌。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