Effect of isoproterenol upon serotonin N-acetyltransferase (SNAT) activity and melatonin production in the chick pineal gland

The administration of isoproterenol to chicks (5 days after hatching) resulted in a modest increase in pineal serotonin N-acetyltransferase (SNAT) activity and a decrease in pineal melatonin levels. The changes observed following isoproterenol administration did not occur consistently in a dose-related or time-course related manner, nor were these changes of the magnitude seen in endogenous nocturnal melatonin levels. Therefore, interpretation of the physiological significance of the isoproterenol-induced changes in melatonin and SNAT must be carefully evaluated.     

松果腺及褪黑素与衰老

衰老是机体随年龄的增长逐渐丧失对环境的适应能力。这个过程伴有行为、内分泌及其他生理功能的改变,使得机体抵抗损伤性刺激的能力降低,对疾病的易感性增加。松果腺的功能随年龄的增加而变化,并与衰老的进程平行。年龄增加松果腺钙化率增高,其生物合成和分泌功能降低,松果腺移植可延缓动物的衰老。褪黑素是吲哚类物质,主要来源于松果腺细胞,血中水平与年龄有关,衰老可导致褪黑素水平下降。外源性褪黑素能延长大鼠的生存期,并能推迟家兔老年性疾病的发生时间。进一步研究发现松果腺和褪黑素延缓衰老与其具有抗自由基作用,调节炎症免疫反应,调节生物钟,影响激素分泌和参与应激等功能有关。而老年期体内自由基清除能力降低、激素分泌紊乱、生物钟衰退、肿瘤及其他疾病的易感性增加正是衰老的重要特征。因此,对褪黑素的深入研究将为抗衰老药的开发开辟新的途径     

松果腺在衰老过程中的地位与褪黑素的作用

目的论述松果腺及褪黑素与机体衰老的因果关系 ,进而提出衰老的松果腺学说。方法 1 本学说提出的背景 ;2 松果腺学说的实验依据 ;3 褪黑素的机能调节作用与抗衰老机理。结果与结论 1 松果腺学说的内容 :衰老源于松果腺形态和功能的变化 ,然后扩展到全身组织细胞 ,呈现多种退行性体征。补充外源性褪黑素或移植松果腺 ,可以延缓老化 ,增长动物寿命。 2 松果腺和褪黑素是年龄变化的函数。随着松果腺钙化 ,褪黑素合成与分泌减少 ,生物节律变得不稳定 ,适应内外环境能力降低。褪黑素在生物界分布极为广泛 ,它作为进化保留分子使机体与环境保持协调统一。褪黑素可在多方面发挥作用 ,通过矫正生物钟功能、调节神经内分泌活动、清除自由基、增强免疫、抗应激、保护遗传物质和促进衰老相关基因表达等 ,起到抗衰老作用。 3 最后阐述松果腺学说的理论意义和应用前景。     

The melatonin generating system in the rat retina and pineal gland: effect of single and repeated electroconvulsive shock (ECS)

N-Acetyltransferase (NAT), a rate-limiting enzyme in the melatonin synthesis which converts serotonin to N-acetylserotonin, shows a distinct circadian rhythm in the rat pineal gland and retina, with low activities during the light phase and peak activities during the dark phase. Hydroxyindole-O-methyltransferase (HIOMT), an enzyme which methylates N-acetylserotonin to melatonin, did not show any significant diurnal variations in both analyzed tissues. Isoproterenol, a selective beta-adrenoceptor agonist, when administered during morning hours of the light phase, markedly increased NAT activity in the pineal gland, but not in the retina. Electroconvulsive shock (ECS), especially when applied repeatedly (ECS x 10, once daily) significantly increased NAT activity in the retina and tended to decrease the enzyme activity in the pineal gland in isoproterenol-treated rats. ECS x 10 slightly increased and decreased the nocturnally-stimulated NAT activity in the rat retina and pineal gland, respectively.     

Pertussis toxin-sensitive G protein modulates the ability of histamine to stimulate cAMP production in the chick pineal gland

Histamine (HA) is a potent stimulator of cAMP synthesis in various structures of chick brain, including the pineal gland. The action of HA is mediated by specific, membrane bound H(2)-like receptors, whose pharmacological profile is different from that described for H(2) receptors in mammalian tissues. In this work, we analyzed the effects of cholera toxin (CTX) and pertussis toxin (PTX), well-known modulators of G(s) and G(i)/G(o) protein, respectively, on the stimulatory action of HA on cAMP synthesis in the chick pineal gland organ cultures. HA and its two biologically active methylated derivatives, 2-methylHA and 4-methylHA, markedly increased cAMP content in the chick pineal glands. Pretreatment of the chick pineal glands with CTX potently stimulated basal cAMP production. In CTX-pretreated glands, elevations of cAMP synthesis evoked by HA, 2-methylHA and 4-methylHA were additive to those produced by CTX, which is an observation suggesting that H(2)-like HA receptors in the chicken pineal gland are not coupled to G(s) proteins. Pretreatment of the chick pineal glands with PTX significantly enhanced the stimulatory effect of HA and, to a greater extent, 2-methylHA on cAMP production. The enhancing action of PTX on the HA-evoked cAMP formation was not modified by mepyramine, a selective H(1)-type HA receptor antagonist. It is suggested that in the chick pineal gland, a population of HA receptors is coupled to G(i) (or G(o)) protein. Stimulation of these receptors would tonically suppress the activity of the cAMP generating system functionally linked to H(2)-like HA receptors.     

Acute treatment with desipramine stimulates melatonin and 6-sulphatoxy melatonin production in man.

Acute administration of the antidepressant drug desipramine (DMI) in man, increased evening melatonin secretion, which reached peak plasma levels 2-4 h earlier than after placebo administration. The increase at set time points 21.00 h-22.00 h was directly proportional to an individual's integrated night-time secretion of melatonin. We have shown that this stimulation was not an effect of DMI inhibition on the hepatic metabolism of melatonin to 6-sulphatoxy melatonin (aMT6s), indeed aMT6s is in itself a good index of the evening melatonin rise. The stimulation of early evening melatonin by DMI might be exploited as a simple pineal function test.     

Effect of psychotropic drugs on the contents of melatonin, serotonin and N-acetylserotonin in rat pineal gland

In the dark phase, the effects of the psychotropic drugs on the contents of melatonin, serotonin (5-HT) and N-acetylserotonin (NAS) in rat pineal gland were examined. The pineal gland was removed at a certain period of time after subcutaneous injection of the drugs. 5-HT, NAS and melatonin contents in the pineal gland were determined by high performance liquid chromatography with fluorometric detection. A dose-dependent decrease was observed for melatonin content in the administration of diazepam (DZP), hydroxyzine (HYZ), chlorpromazine (CPZ) or haloperidol (HPD). When imipramine (IPM) or amitriptyline (APL) was given to rats, pineal 5-HT content was significantly decreased. On the other hand, the administration of IPM or APL caused increases in pineal NAS and melatonin. Furthermore, the administration of phenytoin (PYT) revealed no changes in the content of pineal indoleamines. These results suggest that the psychotropic drugs widely used in clinical applications could cause significant changes in pineal indoleamine content.     

Influences of a light-dark profile and the pineal gland on the hypnotic activity of melatonin in mice and rats

We have investigated the influences of the light-dark cycle and the pineal gland on the hypnotic activity of melatonin in rats and mice. The results showed that melatonin significantly shortened time to sleep onset and wakefulness time, increased slow wave sleep, paradoxical sleep, and total sleep time in rats during the light phase of a 12-h light:12-h dark cycle, by electroencephalogram recording. However, during the dark phase it had almost no significant sleep-promoting effect except shortened time to sleep onset. Melatonin exhibited more potent sleep-promoting effect in rats exposed to constant light compared with rats exposed to 12:12-h light:dark at 2000 h. Melatonin markedly prolonged sleeping time in the mice exposed to constant illumination. It was found that pinealectomy was an important factor that influenced the hypnotic activity of melatonin. When melatonin was administered to pinealectomized mice, the hypnotic activity of melatonin was more intense compared with sham-operated mice. These results demonstrated that the hypnotic activity of melatonin displayed a light-dependence manner. These results suggested that light exposure and the functional state of the pineal gland could substantially impact the hypnotic activity of melatonin at pharmacological dosage.     

Carbaryl-induced changes in indoleamine synthesis in the pineal gland and its effects on nighttime serum melatonin concentrations.

The effects of different doses of chronically administered carbaryl on rat pineal N-acetyltransferase (NAT) activity, hydroxyindole-O-methyltransferase (HIOMT) activity and pineal and serum melatonin levels during darkness (2300 h and 0100 h) when pineal melatonin synthesis is high were studied. Additionally, pineal levels of 5-hydroxytryptophan (5-HTP), serotonin (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) were estimated. Carbaryl was administered at total doses (over 6 days) of either 50, 125 or 250 mg/kg by gastric gavage. Control rats received vehicle (corn oil) only. During the study, the rats were exposed to light/dark cycles of 14:10 with lights off at 2100 h. Pineal NAT and HIOMT activities and pineal melatonin were increased at 0100 h following carbaryl administration at all three doses. Conversely, serum melatonin was increased at 2300 h after the 250 mg/kg dose of carbaryl while all three doses of the pesticide reduced serum melatonin levels at 0100 h. Pineal 5-HTP, 5-HT and 5-HIAA levels were usually increased at 2300 h but unaffected at 0100 h. The results indicate that carbaryl has significant effects on pineal melatonin synthesis and secretion.     

松果体和褪黑激素对大鼠脾淋巴细胞增殖和地诺前列酮产生的影响(英文)

目的:研究松果体和褪黑激素对大鼠脾淋巴细胞增殖及地诺前列酮产生的影响.方法:采用松果体切除术,淋巴细胞增殖反应测定及地诺前列酮放射免疫检定法.结果:大鼠脾淋巴细胞增殖反应存在昼夜节律.松果体切除后,此昼夜节律消失,脾淋巴细胞增殖反应降低,而脾脏地诺前列酮增加.16:00ip褪黑激素(Mel)10 μg·kg~(-1)·d~(-1)连续7 d能恢复之,且促进正常大鼠脾淋巴细胞增殖反应,抑制脾地诺前列酮的产生.结论:松果体Mel促进大鼠脾淋巴细胞增殖反应与抑制脾脏地诺前列酮的产生有关系。     

TCDD decreases rapidly and persistently serum melatonin concentration without morphologically affecting the pineal gland in TCDD-resistant Han/Wistar rats.

The highly toxic environmental contaminant, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was recently reported to decrease serum melatonin levels throughout the circadian cycle in the most TCDD-susceptible strain of rat, Long-Evans. To find out whether this effect is related to the mechanism of acute lethality of TCDD, serum melatonin levels were measured at the nocturnal peak phase in the most TCDD-resistant rat strain variant, Han/Wistar rats, 6 hr to 28 days after TCDD exposure. The same dose as used in the previous study, 50 micrograms/kg, decreased serum melatonin levels to approximately half the control values by the first day after the treatment. Melatonin concentrations remained at this reduced level over the whole observation period. In an auxiliary experiment, Han/Wistar rats were dosed with 1000 micrograms/kg TCDD and killed on day 3. Neither light nor electron microscopic examination of their pineal glands revealed any alteration attributable to TCDD treatment. These findings might indicate that the reduction of serum melatonin levels in the rat by TCDD is not related to its lethal effect and is not due to a direct damage of the pineal gland.     

Effect of benserazide on the levels of pineal 5-hydroxytryptamine,melatonin synthesising enzymes and serum melatonin

The effect of benserazide, an aromatic L-amino acid decarboxylase inhibitor, has been investigated on pineal 5-hydroxytryptamine content, melatonin synthesising enzyme activities and serum melatonin concn. Increasing doses of benserazide caused increasing reductions in the pineal content of 5-hydroxytryptamine. Dark phase serum melatonin concns were also greatly reduced. The drug abolished the diurnal rhythm of hydroxyindole-0-methyltransferase by increasing the light period activities and decreasing the night levels of this enzyme. Pineal N-acetyltransferase was unaffected. It is concluded that benserazide probably inhibits melatonin synthesis by preventing the formation of the substrate, 5-hydroxytryptamine.     

Effect of glucocorticoid dexamethasone on cyclic AMP formation stimulated by pituitary adenylate cyclase-activating polypeptide (PACAP) in the cerebral cortex and hypothalamus of chick.

In this study we tested in chicks the effects of acute and chronic in vivo treatment with a glucocorticoid dexamethasone (4 mg/kg, i.p.) on PACAP-stimulated cyclic AMP formation in [3H]adenine-prelabeled slices of the hypothalamus and cerebral cortex. PACAP (1-100 nM) concentration-dependently stimulated cyclic AMP formation in both brain regions of chick. In acute experiments, dexamethasone (single dose)-injected chicks were killed after 2, 24 and 48 h; while in chronic experiment the glucocorticoid was given once daily for 12 days and the animals were killed 48 h after the last injection. The ability of PACAP to stimulate cyclic AMP formation in the hypothalamus and cerebral cortex was similar in vehicle-treated (control) and dexamethasone-treated animals, with the exception of the nucleotide response to 100 nM of the peptide in both brain regions, which was significantly larger in the group of chicks killed 48 h after the administration of the single steroid dose.     

Effect of venlafaxine on pineal melatonin and noradrenaline in the male rat

Studies in vitro indicate that the antidepressant drug, venlafaxine (VEN), inhibits the reuptake of both serotonin (5-hydroxytryptamine, 5-HT) and noradrenaline (NA) but has little activity on other neurotransmitter receptors. There are, however, few studies on the effects of VEN on monoamine neurotransmission in vivo. In the present study we examined the effect of VEN treatment on the melatonin content of the rat pineal gland because the synthesis of melatonin is regulated by the release of NA onto pinealocyte beta-adrenoceptors. Acute treatment with higher doses (15 mg/kg) of VEN significantly increased pineal melatonin and NA but this effect was attenuated by subchronic treatment. These data are consistent with in vitro data suggesting that VEN increases NA neurotransmission at higher doses and that repeated treatment can desensitize pinealocyte beta-adrenoceptors.     

Antidepressants and protein kinases: desipramine treatment affects pineal gland cAMP-dependent protein kinase activity

To further describe the molecular mechanisms involved in reductions in noradrenergic responsiveness induced by antidepressants, the effects of antidepressant treatment on the rat pineal gland cAMP-dependent protein kinase system were examined. The concentration of cyclic AMP-dependent protein kinase activity was reduced 24 h after acute treatment with desipramine, as well as in animals treated repeatedly with desipramine. Assays performed in the presence of cAMP protein kinase inhibitor showed no significant effects of either acute or repeated desipramine treatment on the concentration of cAMP-independent protein kinase activity. Neither acute nor repeated treatment with other antidepressants (zimelidine, iprindole or fluoxetine) significantly altered the concentration of cAMP-dependent or cAMP-independent protein kinase activity. Using activity ratios to judge the extent of activation of cAMP-dependent protein kinase in vivo, it was found that isoproterenol-induced increases in cAMP protein kinase activity were similar in control and acutely-treated animals, but were reduced with repeated desipramine treatment. The extent of protein kinase activation was also elevated by both acute and repeated treatment in the absence of isoproterenol. In further studies, desipramine (10 microM) did not directly affect activation of the kinase by cAMP or maximum kinase catalytic activity. These results show that the concentration and extent of activation of cAMP protein kinase is altered following desipramine treatment in the rat pineal gland and that modulation of cAMP protein kinase may be a locus of regulation for desipramine-mediated reduction in noradrenergic responsiveness.     

Pineal gland and melatonin influence on chronic alcohol consumption by hamsters

Male golden hamsters preferentially consume alcohol solution when given a free-choice between water and the alcohol solution. The pineal gland has been implicated as influencing the predilection for the ethanol solution. Melatonin, a pineal hormone, was administered either daily for 11 weeks as a subcutaneous injection (25 μg/animal) or weekly as a subcutaneous beeswax implant (1 mg melatonin/24 mg beeswax) for 5 weeks to hamsters allowed a free-choice between water or a 10% ethanol solution. Food, water and alcohol consumptions were measured on a daily basis. Animals treated by daily injection with melatonin consumed slightly less ethanol than animals not given melatonin. In light-deprived animals given chronic implants of melatonin, alcohol consumption was reduced when compared to alcohol consumption by light-deprived hamsters not receiving melatonin. Melatonin treatment also resulted in reducing daily total fluid intake as well as ethanol consumption in light-deprived hamsters. The results indicate that the pineal gland may influence fluid consumption in the hamster, and indirectly alters the propensity of the hamster to consume alcohol.     

Regulation of serotonin N-acetyltransferase activity in the chick pineal gland by UV-A and white light: role of MK-801- and SCH 23390-sensitive retinal signals

The rhythmic melatonin synthesis in the pineal gland is one of the most extensively studied circadian rhythms in vertebrates. Light is the dominant environmental factor controlling this process. Light at night acutely suppresses pineal melatonin content and activity of serotonin N-acetyltransferase (AANAT; the key and penultimate enzyme in the hormone biosynthetic pathway). In addition, pulses of light appropriately timed reset the circadian oscillator generating the melatonin rhythm. Although the avian pineal gland is a directly photosensitive organ, it has recently been demonstrated that light perceived by the eyes only regulates its activity. The present study shows that ocular exposure of chicks to UV-A radiation or white light during the second half of the subjective night markedly decreased AANAT activity in the pineal gland, and produced a significant phase advance of the circadian rhythm of the enzyme activity. Both the suppressive and phase-shifting effects of UV-A light were antagonized by intraocular pretreatment of birds with MK 801 (a selective blocker of NMDA glutamate receptors), but were not modified by SCH 23390 (a selective antagonist of D1-dopamine receptors). On the other hand, the suppressive and phase-shifting effects of retinally perceived white light were antagonized by intraocular injection of SCH 23390, and not affected by MK 801. Our results demonstrate that retinal illumination with UV-A radiation and white light provide powerful signals that shift phase of the circadian oscillator generating melatonin rhythm in the chick pineal gland. It is suggested that control of pineal melatonin synthesis by retinally perceived UV-A and white light might involve input from different photoreceptors.