Effects of 2-mercaptoethylguanidine and other compounds on norepinephrine synthesis by adrenal medullary granules

The effects of 2-mercaptoethylguanidine and other compounds on dopamine uptake and norepinephrine synthesis by adrenal medullary granules were studied. The effects of these materials on crude dopamine-β-hydroxylase were also tested. A microanalytical technique was developed which allows the use of the natural precursor, dopamine, in studies of uptake and synthesis by adrenal medullary granules. The conversion of dopamine to norepinephrine by dopamine-β-hydroxylase was also studied with this technique. Catecholamines were assayed as their dansyl (5-dimethylaminonaphthalene-1-sulfonyl) derivatives, thereby increasing greatly the resolution and sensitivity of detection. The effects of 2-mercaptoethylguanidine and reserpine on dopamine uptake and norepinephrine synthesis by medullary granules were compared. Reserpine inhibited norepinephrine synthesis indirectly through inhibition of dopamine uptake. 2-Mercaptoethylguanidine, on the other hand, depressed norepinephrine synthesis in intact granules by a direct inhibitory effect on dopamine-β-hydroxylase rather than on the uptake mechanism. 2-Mercaptoethylguanidine increased the rate of norepinephrine synthesis by crude dopamine-β-hydroxylase in the presence of added Cu²⁺ and inhibited norepinephrine synthesis in the absence of added Cu²⁺. The nature of the latter effect was resolved by demonstrating the formation of a Cu-2-mercaptoethyl-guanidine complex in pure solutions. Since dopamine-β-hydroxylase is a Cu-containing enzyme, the mechanism of the 2-mercaptoethylguanidine inhibition of dopamine-β-hydroxylase appears to be through the binding of enzymic Cu.     

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.     

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.     

In vitro screening of food peptides toxic for coeliac and other gluten-sensitive patients: a review

Experience gained through investigations on coeliac disease makes it possible to propose a screening method based on agglutination of isolated K562(S) cells to evaluate the occurrence in food protein of amino acid sequences that are able to adversely affect coeliac and related gluten-sensitive patients. The method consists of in vitro sequential peptic and tryptic digestion of food protein fractions under optimal pH, temperature and time conditions and in vitro incubation of the digest with K562(S) cells; the toxic potential is detected as an agglutination of K 562 (S) cells after a short incubation. Other in vitro test systems, including atrophic coeliac intestinal mucosa and rat fetal intestine, can be used to confirm the results obtained with the isolated cells. A fractionation step of the proteolytic digest on a sepharose-mannan column before exposure of the in vitro systems to the separated peptide fractions adds to the sensitivity of the method. This screening method is not only very useful to investigate action mechanisms in coeliac disease, but also to assess the safety of genetically-modified plant foods and novel foods for gluten-sensitive patients.     

Hypotensive activity of the pineal indoleamine hormones melatonin, 5-methoxytryptophol and 5-methoxytryptamine

Injection of the pineal indoles melatonin, 5-methoxytryptophol and 5-methoxytryptamine via the external jugular vein elicited a dose-dependent depression in mean arterial pressure. Melatonin and 5-methoxytryptophol were approximately equipotent and a dose of 150 micromol/kg brought about a reduction of about 40 mmHg in mean arterial pressure. Methoxytryptamine exerted a much more potent hypotensive action. An abrupt decrement in mean arterial pressure by 30 mmHg occurred when the dose was only 2 nmol/kg. Subsequent increases in the dose further lowered the mean arterial pressure, but more gently. The other pineal indoles tested including 5-methoxyindoleacetic acid and 5-hydroxyindoleacetic acid, as well as 6-methoxy-2-benzoxazolinone, did not affect the mean arterial pressure when tested up to 80 micromol/kg. Methylene blue, a guanylate cyclase inhibitor, was not able to antagonize the hypotensive activity of melatonin, suggesting that the mechanism of action of melatonin does not involve guanylate cyclase. Lidocaine, which blocks sodium channels in perivascular nerves, antagonized the hypotensive action of melatonin.     

Effects of P-chlorophenylalanine on pineal and endocrine function in the rat

This study attempted to determine whether brain serotonin (5-HT), which is altered by melatonin administration, is involved in mediating the effects of melatonin on basal endocrine function. Pineal melatonin levels, serum N-acetylserotonin (NAS) levels, adrenocortical activity, and other endocrine parameters were measured following 5-HT depletion by p-chlorophenylalanine (p-CPA) together with either pineal stimulation by blinding or blinding plus pinealectomy. Blinding increased pineal melatonin levels in both saline and p-CPA treated animals. P-CPA treatment increased adrenal weights and morning plasma corticosterone levels in both blinded and blinded-pinealectomized animals. Conversely, p-CPA depressed pineal melatonin levels and serum NAS but elevated morning plasma corticosterone levels in sighted controls. P-CPA also decreased plasma prolactin and growth hormone levels in intact animals. These findings suggest that 5-HT inhibits morning corticosterone secretion and stimulates prolactin and growth hormone release. In addition, melatonin and serotonin may function independently in regulating adrenocortical function, while melatonin's effect is superceded by that of serotonin.     

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。     

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.     

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.     

Molecular mechanisms of the pro-apoptotic actions of melatonin in cancer: a review

Introduction: Compelling evidence has highlighted the complex pleiotropic functions elicited by the melatonin in cancer cells. Melatonin behaves as a ‘smart killer', i.e., modulating anti-apoptotic processes in normal cells, and triggering pro-apoptotic signals in cancer cells.

Areas covered: Melatonin induces programmed cell death in a wide range of different tumors (breast, gastro-intestinal, hematological, prostate, osteosarcoma, melanoma, kidney, etc…). Mechanisms of action and molecular pathways involved in pro-apoptotic processes under melatonin treatment are discussed.

Expert opinion: Melatonin involvement in apoptotic processes is a new and relevant field of investigation. Even in tumor models unresponsive to melatonin alone, this hormone can significantly amplify the cytostatic and the cytotoxic effects triggered by other compounds or conventional drugs. We are far from having a satisfactory understanding about how and when melatonin exerts its beneficial effects. Melatonin in the nanomolar range activates the intrinsic and/or the extrinsic apoptotic pathway in cancer cells, namely through an increase in the p53/MDM2p ratio and downregulation of Sirt1. This finding is of great relevance since there is intense research ongoing to identify nontoxic feasible inhibitors of MDM2 and Sirt1. Melatonin should be evaluated for the management of those cancers where both of these are overexpressed and functionally strategic.     

MDMA-induced impairment in primates: antagonism by a selective norepinephrine or serotonin, but not by a dopamine/norepinephrine transport inhibitor

Human MDMA (R,S-3,4-methylenedioxymethamphetamine) users display selective cognitive deficits after acute MDMA exposure, frequently attributed to serotonin deficits. We postulated that MDMA will compromise executive function in primates and that an inhibitor of the serotonin transporter (SERT) and the norepinephrine transporter (NET) but not the dopamine (DAT) transporter, will prevent impairment. The potencies of DAT/NET, NET and SERT inhibitors to block transport of [(3)H]MDMA and [(3)H]monoamines were compared in vitro. Subsequently, cynomolgus monkeys (Macaca fasicularis) were trained to stable performance in a reversal learning task. Effects of once-weekly oral or i.m. dose of MDMA (1.5 mg/kg, n = 4) on performance were monitored, alone or after pretreatment with inhibitors of the SERT, DAT or NET (prior to i.m. MDMA). 1) Drug potencies for blocking [(3)H]MDMA or [(3)H]monoamine transport were not consistent; 2) Oral MDMA increased error rates in a cognitive task for up to three days following exposure, whereas intramuscular MDMA prevented subjects from performing the cognitive task on the day of administration, but not on subsequent days; 3) The SERT inhibitor citalopram and the NET inhibitor desipramine, but not the DAT/NET inhibitor methylphenidate, reversed the effects of MDMA on task performance and mandibular movements induced by i.m. MDMA and 4) MDMA altered sleep latency. Oral MDMA impairs executive function in monkeys for several days, a finding of potential relevance to MDMA consumption by humans. Reversal of impaired executive function by a NET inhibitor implicates the NET and norepinephrine in MDMA-induced cognitive impairment and may be relevant to therapeutic strategies.     

褪黑素对大鼠脑内β-内啡肽、去甲肾上腺素和5-羟色胺释放的影响

目的　观察褪黑素(MLT)对大鼠脑内β-内啡肽(β-Ep)、去甲肾上腺素(NE)及5-羟色胺(5-HT)释放的影响,以探讨MLT镇痛作用机制。方法　结合痛阈测定,放免测定第三脑室推挽灌流液中β-Ep样免疫活性物质(ir-βEp)含量;高效液相色谱法测定脑内微透析液中NE和5-HT的代谢产物。结果　ipMLT110mg·kg^-1可显著增加第三脑室灌流液中ir-βEp含量,同时显著提高大鼠痛阈;但对中脑导水管周围灰质(PAG)、下丘脑微透析液中3-甲氧基-4-羟基苯乙二醇、5-羟吲哚乙酸含量无显著影响。结论　MLT可促进脑内β-Ep的释放,可能是其镇痛作用的机制之一;MLT的镇痛作用与PAG、下丘脑内NE、5-HT的释放可能无关。     

Implications of melatonin therapy in irritable bowel syndrome: a systematic review

Irritable bowel syndrome (IBS) is a highly prevalent chronic functional gastrointestinal (GI) disorder associated with abdominal pain and change in bowel habits that its etiology is not known yet. In the recent years, melatonin has been proposed as a possible candidate. In the present work, all clinical or non-clinical data about effects of melatonin in GI tract and IBS obtained from literature without time limit up to August 2010 have been studied and reviewed. Eight clinical trials were reviewed for efficacy and disturbance of melatonin in IBS and other GI disorders. The results showed disturbances in endogenous melatonin concentration in IBS patients and significant benefits of exogenous melatonin in these patients by decreasing abdominal pain and improvement of overall IBS symptom scores. The results of seventeen non-clinical studies showed anxiolytic, anti-inflammatory, anti oxidative and motility regulatory effects of melatonin on GI tract. In conclusion melatonin can be a target of interest in IBS because of its potentials to regulate GI motility.