The pineal and melatonin: Regulators of circadian function in lower vertebrates

Summary The pineal has been identified as a major circadian pacemaker within the circadian system of a number of lower vertebrates although other pacemaking sites have been implicated as well. The rhythmic synthesis and secretion of the pineal hormone, melatonin, is suggested as the mechanism by which the pineal controls circadian oscillators located elsewhere. Both light and temperature cycles can entrain the pineal melatonin rhythm. The pineal, therefore, acts as a photo and thermoendocrine transducer which functions to synchronize internal cycle with cycles in the environment. A model is presented which portrays the pineal as a major component of a multioscillator circadian system and which suggests how these multiple circadian clocks are coupled to each other and to cycles of light and temperature in the external world.     

褪黑激素被动免疫对母鸭卵泡发育和垂体激素水平的影响

在秋冬光照变短季节,选择产蛋量已下降的68周龄仙湖三号母鸭30只,随机分成三组。试验组用效价为1∶3200的兔化褪黑激素血清抗体进行被动免疫,对照组用正常兔血清进行被动免疫。在第三次免疫3h后每组随机选择6只母鸭采集血液,每隔4h采血1次,血样采用化学发光定量免疫分析测定血浆中的FSH,LH的含量,采完血后剖检卵巢,对卵泡进行分级计数。结果表明,经过三次免疫,可提高FSH水平(P>0.05),但对卵泡发育的影响差异不显著。提示在短日照下通过被动免疫可中和母鸭体内MLT,增加母鸭垂体激素水平,对母鸭生殖机能具有一定的激发作用。     

褪黑素生理及药理作用研究进展

松果体褪黑素作为一种可能的药物已引起国内外医学界的广泛关注，其作为药物的典型特征是作用剂量低(10^-9mol)、药效温和、无毒副作用。大量临床试验的结果表明，褪黑素具抗肿瘤、抗氧化、增强机体免疫力和清除体内自由基等多种重要的生理和药理作用，极可能成为一种在治疗肿瘤方面广泛应用的临床药物。综述了褪黑素在上述方面的生理和药理作用，并展望了其应用前景。     

Neither prolactin nor growth hormone restore the nocturnal rise in pineal N-acetyltransferase activity or melatonin content in hypophysectomized rats

Summary Hypophysectomy in adult male rats greatly attenuated the nocturnal rise in both pineal N-acetyltransferase (NAT) activity and melatonin content. High nighttime levels of NAT and melatonin were not restored by treating the animals with either prolactin or growth hormone, alone or in combination. Treating intact rats with bromocriptine, which depresses circulating prolactin levels, also was without effect on pineal melatonin synthesis. It appears that neither prolactin nor growth hormone are of major importance in determining pineal melatonin production.     

Evidence for a modulation of the stress response by the pineal gland

Summary Wistar rats show a circadian variation in their response to stress. Pinealectomy exacerbates stress-induced gastric ulceration in rats. This effect is counteracted by melatonin administration.     

Effects of vitamin B12 on plasma melatonin rhythm in humans: Increased light sensitivity phase-advances the circadian clock?

Vitamin B12 (methylcobalamine) was administered orally (3 mg/day) to 9 healthy subjects for 4 weeks. Nocturnal melatonin levels after exposure to bright light (ca. 2500 lx) were determined, as well as the levels of plasma melatonin over 24 h. The timing of sleep was also recorded. Vitamin B12 was given blind to the subjects and crossed over with placebo. We found that the 24-h melatlonin rhythm was significantly phase-advanced (1.1. h) in the vitamin B12 trial as compared with that in the placebo trial. In addition, the 24-h mean of plasma melatonin level was much lower in the vitamin B12 traial than with the placebo. Furthermore, the nocturnal melatonin levels during bright light exposure were significantly lower in the vitamin B12 trial than with the placebo. On the other hand, vitamin B12 did not affect the timing of sleep. These findings raise the possibility that vitamin B12 phase-advances the human circadian rhythm by increasing the light sensitivity of the circadian clock.