Dose dependent effects of S-20098, a melatonin agonist,on direction of re-entrainment of rat circadian activity rhythms

The chronobiotic properties of melatonin are well documented. For example, following an 8-h phase advance of the light-dark cycle daily injections of melatonin administered at the pre-shift dark onset alter the direction of re-entrainment of rat activity rhythms. Using this 8-h phase advance paradigm, the effects of the melatonin agonist S-20098 (1 mg/kg and 3 mg/kg) on the rat circadian system were compared with those of melatonin. S-20098 altered the direction of reentrainment in the same manner as melatonin. A study using lower doses of S-20098 showed that the effect on direction of re-entrainment was dose-dependent, with 100% of rats responding at a dose of 100 µg/kg. S-20098 may, therefore, have therapeutic potential as a chronobiotic in the treatment of circadian disorders in humans.     

Application of in vivo microdialysis to pineal research in birds: Measurement of circadian rhythms of melatonin

Circadian rhythms of pineal melatonin release were measured in free-moving pigeons, Japanese quails, and chickens under light-dark cycles followed by constant dim light. Although melatonin levels differed among individual birds, circadian rhythms of melatonin were observed in all of them. Using this technique, we could examine phase shifts of melatonin rhythms and suppression of melatonin release by photic stimulation in pigeons. We could also examine effects of norepinephrine infusion on melatonin release. These results indicate that microdialysis is useful for the study of pineal melatonin rhythms in birds.     

褪黑素在鸡脊柱侧凸模型中的影响

目的　通过鸡松果体蒂部切断的方法 ,研究褪黑素在松果体切除鸡脊柱侧凸动物模型中的作用。方法　 10只刚孵育出的WhiteLeghorn鸡作为对照组 ,未行任何处理 ,控制白天 12h光照 (强度 5 0 0Lux)、夜间 12h完全黑暗 (强度 0 - 5lux)条件下饲养 ;2 0只WhiteLeghorn鸡在鸡龄 3d时行松果体切除 ,控制光照条件同对照组 ;2 0只WhiteLeghorn鸡 3d时行松果体蒂部切断术 ,控制光照同对照组。 5周时留取所有鸡白天 (mid -day)和夜间 (mid -night)的血清 ,用RIA试剂盒测定血清中褪黑素含量。所有的鸡处死后 ,取骨骼标本 ,行脊柱前后位平片检查。结果　 5周时 ,对照组褪黑素含量呈现明显白天低 (5 7.2 5± 7.4 3)pg/ml,夜间高 (2 5 7.92± 2 6 .0 9)pg/ml的周期性变化。松果体切除组褪黑素含量 ,白天为 (6 0 .0 5± 5 .4 8)pg/ml,夜间为 (5 5 .0 9± 8.35 )pg/ml,其分泌维持低水平。松果体蒂部切断组褪黑素含量 ,白天为 (5 8.77± 8.4 4 )pg/ml,夜间为 (2 4 8.4 7± 2 7.2 1)pg/ml,仍呈白天低 ,夜间高的周期性变化。X线检查 :对照组 10只鸡无脊柱侧凸发生 ;松果体切除组 2 0只鸡中 9只鸡发生了脊柱侧凸 ,发生率为 4 5 % ;松果体蒂部切断组 2 0只鸡中有 11只发生了侧弯 ,发生率为 5 5 %。结论　松果体切除和松果体蒂部     

Influence of melatonin on bovine pulmonary vascular and bronchial airway smooth muscle tone

The influence of melatonin on tension of isolated bovine pulmonary vascular and bronchial smooth muscle rings were examined in these experiments. Melatonin caused a dose-dependent relaxation of precontracted (30 mM KCl) pulmonary artery and vein, although the effect is greater in arterial smooth muscle. This relaxant response was blocked by preincubating vessels with antagonists of vasoactive intestinal peptide or Substance P. In bronchial smooth muscle, melatonin caused a small contractile response. These experiments demonstrate that in response to melatonin the pulmonary vasculature relaxes, while in airway smooth muscle the reverse, constriction, occurs. It is hypothesized that nocturnal exaggeration of asthma may, in part, be due to changes in circulating levels of melatonin.     

Pineal response after pyridoxine test in children

Summary To characterize the pineal response to pyridoxine, plasma melatonin was measured in one hundred and twenty children 3 hours after vitamin B₆ administration. The children, aged between 1.5 and 8 years, were divided in four groups as follows: a) control day group, grouping 27 children sampled at 9:00 and at 12:00; b) control night group, grouping 29 children sampled at 21:00 and at 24:00; c) pyridoxine day group, grouping 30 children sampled at 9:00, then intravenously (i.v.) injected with 3mg/kg of pyridoxine, and sampled at 12:00; and d) pyridoxine night group, grouping 34 children sampled at 21:00, i.v. injected with 3mg/kg of pyridoxine, and sampled at 24:00. Melatonin concentration was measured by radioimmuno assay. The data obtained showed a significant increase in melatonin levels after pyridoxine administration in the pyridoxine night group (39.87 ± 8.02pg/ml basal vs 88.45 ± 9.21 pg/ml after pyridoxine, p < 0.001). The other groups did not showed significant differences in melatonin concentrations. Statistical analysis shows that the administration of pyridoxine during the nocturnal hours represents a stimulating factor to increase the pineal production of melatonin in children.     

Effects of pinealectomy and exogenous melatonin on rat hearts

The effects of pinealectomy and administration of melatonin, the major secretory product of the pineal gland, which is a direct free radical scavenger and an indirect antioxidant, were studied in rat hearts on the basis of cardiac morphology and biochemical findings. Three groups of Wistar rats were used: one group was the sham-operated control, one group consisted of pinealectomized rats and one group consisted of pinealectomized rats that were treated with melatonin. Serum cholesterol, tissue levels of malondialdehyde (MDA) and reduced glutathione (GSH), and heart weight were determined. Histochemical staining with the Van Gieson, PAS/Alcian blue at pH 2.5 and Masson's trichrome methods were performed in addition to hematoxylin-eosin staining. Levels of serum cholesterol and tissue MDA, and heart weight were increased in pinealectomized rats whereas GSH levels did not change. Melatonin administration reversed these effects. Microscopically, myocardial fibrosis and myxomatous degeneration of cardiac valves were detected in all pinealectomized rats. It can be concluded that pinealectomy of rats causes morphological changes in rat hearts, and short-term application of melatonin does not reverse these changes.     

人外周血淋巴细胞褪黑素受体的基因与蛋白表达的研究

目的:研究人外周血淋巴细胞褪黑素受体(MR)的基因与蛋白表达的特点。方法:分离健康成年人外周血淋巴细胞,采用异硫氢酸胍-苯酚-氯仿一步法抽提总RNA,分别采用Northern印迹和RT-PCR方法检测MR亚型mt₁和MT₂的mRNA,并将RT-PCR的阳性产物通过自动测序仪测序;同时应用免疫组化染色方法检测mt₁和MT₂受体亚型蛋白在淋巴细胞内的分布特点。结果:Northern印迹方法检测出长约1.1 kb mt₁ mRNA,但未检出长约1.1 kb MT₂ 的mRNA;RT-PCR方法则得到了368 bp mt₁ cDNA片段,无321 bp MT₂ cDNA片段,同时将mt₁阳性条带通过胶回收、测序,结果显示扩增产物与人mt₁受体亚型的基因序列相吻合;免疫组化结果显示:人外周血淋巴细胞存在mt₁受体蛋白,主要分布于细胞膜和细胞浆,呈棕褐色阳性颗粒,而细胞核上未见阳性颗粒,MT₂受体蛋白则未检出。结论:证实正常人外周血淋巴细胞存在mt₁的基因与蛋白的表达,而无MT₂的基因与蛋白的表达,提示外周血淋巴细胞为褪黑素(Mel)作用的外周靶器官,为研究生理及病理情况下Mel对免疫系统的调节奠定了基础。     

Androgenic control of porphyrin in the harderian glands of the male syrian hamster is modulated by the photoperiod,which suggests that the sexual differences in porphyrin concentrations in this gland are important functionally

Background: The porphyrin concentrations of the Harderian glands of Syrian hamsters show marked sexual differences, with male levels being much lower than those of females. Porphyrinogenesis is inhibited by androgens, so orchidectomy leads to elevated male porphyrin concentrations; however, a number of other procedures (some of which also lower androgen levels) prevent this. We studied the effects of short-day photoperiods and melatonin on Harderian porphyrin concentrations. Methods: Intact, castrated, or pinealectomized hamsters of both sexes were exposed to long-day or short-day photoperiods. Intact or castrated hamsters were given melatonin injections in the morning or the afternoon, or were given beeswax pellets containing melatonin. After a variable period, Harderian glands were dissected and porphyrins were measured. Results: Prolonged short-day exposure (13 weeks) led to increased Harderian porphyrin concentrations and this rise was prevented by pinealectomy. The rise in Harderian porphyrins following short-day exposure was small, compared with that following castration. Short-day photoperiods also prevented the rise in porphyrin levels associated with castration and this effect was prevented by removal of the pineal. Melatonin injections, whether given in the morning or in the afternoon, had no effect on Harderian porphyrin concentration of castrated male hamsters. Continuous release melatonin pellets reduced the postcastrational rise in porphyrin levels in one experiment, while having no effect in another. In female hamster, neither short photoperiods nor melatonin pellets influenced Harderian porphyrin concentrations. Conclusions: These results suggested that a factor from the pineal gland helps maintain the low levels of porphyrin which are characteristic of male Harderian glands, despite the decrease in androgen levels which typically results from exposure to short days. Morning and afternoon injections of melatonin and continuous release melatonin pellets failed to resolve the question of whether this pineal factor is melatonin. Our results demonstrated that low male and high female porphyrin levels are maintained in Syrian hamsters, despite seasonal variations in the hormonal milieu, suggesting that these sexual differences are important for the (still unestablished) function of the Harderian glands in this species. © 1994 Wiley-Liss, Inc.     

Dual effects of melatonin on barbiturate-induced narcosis in rats

Melatonin affects the circadian sleep/wake cycle, but it is not clear whether it may influence drug-induced narcosis. Sodium thiopenthal was administered intraperitoneally into male rats pre-treated with melatonin (0.05, 0.5, 5 and 50 mg/kg). Melatonin pre-treatment affected in a dual manner barbiturate narcosis, however, no dose-effect correlation was found. In particular, low doses reduced the latency to and prolonged the duration of barbiturate narcosis. In contrast, the highest dose of melatonin (50 mg/kg) caused a paradoxical increase in the latency and produced a sustained reduction of the duration of narcosis, and a reduction in mortality rate. Melatonin 0.5 and 5 mg/kg influenced the duration but not the latency of ketamine- or diazepam-induced narcosis. Thus, the dual action of melatonin on pharmacological narcosis seems to be specific for the barbiturate mechanism of action.