Delayed sexual maturation induced by daily melatonin administration eliminates the LH response to naloxone despite normal responsiveness to GnRH in juvenile male rats.
Delayed sexual maturation induced by daily melatonin administration eliminates the LH response to naloxone despite normal responsiveness to GnRH in juvenile male rats.
复制标题
尽管幼年雄性大鼠对 GnRH 的反应正常，但每日服用褪黑激素诱导的性成熟延迟消除了 LH 对纳洛酮的反应。
作者：
M. Aubert;R. Rivest;U. Lang;B. P. Winiger;P. Sizonenko
每日给予褪黑激素（MT）可显着延迟雄性 Wistar 大鼠的性成熟。在这项研究中，我们评估了正常幼年雄性大鼠和从出生 20 天开始每天下午注射 MT（100 微克，皮下注射）诱导性发育延迟的大鼠的垂体对 GnRH 的反应性以及内源性阿片类药物的强直抑制水平。尽管垂体 GnRH 受体数量显着减少且垂体促性腺激素含量降低，但 MT 治疗的大鼠在生命 30 天和 40 天时，对重复静脉内 GnRH 给药（100 ng/100 g 体重）或皮下给予不同剂量 GnRH（5-100 ng/100 g 体重）的血浆 LH 反应均正常。注射一次纳洛酮 (NAL)（2.5-5.0 mg/kg，皮下注射）可使正常 40 日龄和 55 日龄大鼠血浆 LH 显着增加，而在 MT 治疗的同龄大鼠中未观察到这种情况。相比之下，30 日龄对照大鼠和 MT 治疗大鼠中血浆 LH 均未见增加。用硫酸吗啡（10 mg/kg，皮下注射）或强效甲硫氨酸脑啡肽类似物 FK 33-824（1.0 mg/kg，皮下注射）进行预处理可防止对照大鼠在第 40 天时 NAL 诱导的血浆 LH 升高。在所有情况下，未经治疗和 MT 治疗的大鼠在 NAL 后血浆 PRL 水平均下降。（摘要截断为 250 字）
Daily administration of melatonin (MT) markedly delays sexual maturation in the male Wistar rat. In this study, we have evaluated pituitary responsiveness to GnRH and the level of tonic inhibition by endogenous opioids in normal juvenile male rats and in rats with delayed sexual development induced by daily afternoon MT injection (100 micrograms, s.c.) starting at 20 days of life. Plasma LH responses to repetitive intravenous GnRH administration (100 ng/100 g body weight), or to different doses of GnRH administered subcutaneously (5-100 ng/100 g body weight) were normal in MT-treated rats both at 30 and 40 days of life despite significantly lower number of pituitary GnRH receptors and decreased pituitary gonadotropin content. One naloxone (NAL) injection (2.5-5.0 mg/kg, s.c.) produced a significant increase of plasma LH in normal 40- and 55-day-old rats, which was not seen in MT-treated rats of the same age. In contrast, no increase of plasma LH was seen in 30-day-old control rats nor in MT-treated rats at this age. Pretreatment with morphine sulfate (10 mg/kg, s.c.), or with the potent Met-enkephalin analog FK 33-824 (1.0 mg/kg, s.c.) prevented the NAL-induced rise of plasma LH in control rats at day 40 of life. In all instances, plasma PRL levels were decreased after NAL both in untreated and in MT-treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)