Search PubMed⌕ Search

Biomedical subjects

N Zisapel

Publications and source records attributed to N Zisapel.

At least 55 records · Page 3Linked to original sources
PubMed1996

Reciprocal effects of chronic diazepam and melatonin on brain melatonin and benzodiazepine binding sites.

Recent reports indicate that benzodiazepines can suppress melatonin levels and that melatonin can increase brain benzodiazepine binding. We have studied the possibility of reciprocal effects of chronic diazepam and melatonin on brain melatonin and benzodiazepine binding sites. Daily injections (3 weeks) of diazepam markedly reduced 125I-melatonin binding site density in the medulla-pons but not cortex of male rats, whereas benzodiazepine binding was not significantly affected. Melatonin, administered via the drinking water, significantly enhanced benzodiazepine (3H-RO 15-1788) binding in the medulla-pons and slightly reduced it in the cortex, but did not affect 125I-melatonin binding. Diazepam and melatonin combination reversed the suppression by diazepam of 125I-melatonin binding in the medulla-pons and the suppression by melatonin of benzodiazepine (3H-RO 15-1788 and 3H-flunitrazepam) binding in the cerebral cortex. These results indicate benzodiazepine-mediated suppression of brain melatonin binding sites that can be abrogated by melatonin administration.

Animals↗
PubMed1996

Functional melatonin receptors in human prostate epithelial cells.

Melatonin, secreted nocturnally by the pineal gland, affects gonadal growth and pubertal development in rodents and, presumably, in humans. Recently, we have found, using 125I-labeled melatonin as a probe, specific melatonin binding sites in the human benign prostate tissue; these sites were primarily associated with the microsomal fraction of the epithelial cells. In the present study, we have explored 125I-melatonin binding sites in human benign prostate epithelial cells in culture and investigated the effects of melatonin on growth and viability of these cells. 125I-melatonin bound to the prostate cells with high (K(d) = 68 pM) affinity. Competition experiments revealed that specific binding was inhibited by subnanomolar concentrations of melatonin and 2-iodomelatonin, whereas serotonin and 5-methoxytryptamine reduced the binding only partially. Melatonin (10 pM-10 nM) inhibited the incorporation of 3H-thymidine and 3H-uridine into the prostate epithelial cells in a dose-dependent manner. Inhibition was transient, and the incorporation recovered to control levels within less than 24 h. Protein synthesis as measured by the incorporation of 35S-methionine into cell proteins decayed to minimal levels about 2 h after addition of melatonin, and its recovery was slower compared with that of 3H-thymidine or 3H-uridine incorporation. Melatonin treatment (1 nM) for 2-7 days inhibited cell growth and markedly increased the percentage of non-viable cells in culture, measured by the trypan blue exclusion assay. The results demonstrate high affinity melatonin receptors in the human benign prostate epithelial cells, which may affect cell growth and viability.

Binding Sites↗
PubMed1996

Putative melatonin receptors in benign human prostate tissue.

Melatonin, secreted by the pineal gland at night, inhibits pubertal development of rats and presumably men. In addition, it may directly suppress prostate growth in the adult rat. To investigate the possibility for a causal relationship between the age-related decline in melatonin production and increase in prevalence of benign prostate hypertrophy (BPH) in man, the presence of melatonin binding sites in human BPH tissue was examined. In vitro autoradiography indicated specific 125I-labeled melatonin (125I-melatonin) binding in the prostate, localized to the glandular epithelium. Separation and subcellular fractionation indicated that these sites were associated with the microsomal fraction of the epithelial cells. Kinetic and equilibrium 125I-melatonin binding experiments revealed that the binding was time dependent and reversible, with an apparent half saturation at 140 pmol/L. Competition experiments indicated high and low affinity melatonin binding sites; binding was inhibited by melatonin (IC50 1 nmol/L and 1 micromol/L, respectively) and partially by the putative melatonin antagonist, N-(2,4 dinitrophenyl)-5-methoxytryptamine (ML-23; IC50 0.1 nmol/L). Serotonin and 6-hydroxymelatonin were less potent, whereas up to 0.1 mmol/Lol/L of 5-methoxytryptamine, 6-methoxymelatonin, and tryptamine caused only a partial reduction in specific binding. The guanine nucleotide analogs, guanosine 5'-O-[3-thiotriphosphate] and guanosine 5'-O-[2-thio-diphosphate, inhibited specific 125I-melatonin binding, whereas 5'-guanylyl imidodiphosphate was less potent. The results indicate putative melatonin receptors in the human prostate epithelium.

Aged↗
PubMed1995

The modulatory effect of melatonin on the dopamine-glutamate interaction in the anterior hypothalamus during ageing.

We investigated the effects of melatonin on the dopamine-glutamate interaction in the anterior hypothalamus of young, middle-aged and aged rats. In young rats, under the effects of amphetamine, melatonin produced an inhibition of dopamine release and a significant increase in glutamate and aspartate release. In middle-aged and aged rats, the inhibitory effects of melatonin on amphetamine-evoked dopamine release were maintained, but no effects on glutamate or aspartate release were found. These results suggest that, during ageing, the modulatory effect of melatonin on dopamine release in rat anterior hypothalamus is preserved whereas the dopamine-glutamate interaction is disrupted with age.

Aging↗
PubMed1995

Improvement of sleep quality in elderly people by controlled-release melatonin.

Melatonin, produced by the pineal gland at night, has a role in regulation of the sleep-wake cycle. Among elderly people, even those who are healthy, the frequency of sleep disorders is high and there is an association with impairment of melatonin production. We investigated the effect of a controlled-release formulation of melatonin on sleep quality in 12 elderly subjects (aged 76 [SD 8] years) who were receiving various medications for chronic illnesses and who complained of insomnia. In all 12 subjects the peak excretion of the main melatonin metabolite 6-sulphatoxymelatonin during the night was lower than normal and/or delayed in comparison with non-insomniac elderly people. In a randomised, double-blind, crossover study the subjects were treated for 3 weeks with 2 mg per night of controlled-release melatonin and for 3 weeks with placebo, with a week's washout period. Sleep quality was objectively monitored by wrist actigraphy. Sleep efficiency was significantly greater after melatonin than after placebo (83 [SE 4] vs 75 [3]%, p < 0.001) and wake time after sleep onset was significantly shorter (49 [14] vs 73 [13] min, p < 0.001). Sleep latency decreased, but not significantly (19 [5] vs 33 [7] min, p = 0.088). Total sleep time was not affected. The only adverse effects reported were two cases of pruritus, one during melatonin and one during placebo treatment; both resolved spontaneously. Melatonin deficiency may have an important role in the high frequency of insomnia among elderly people. Controlled-release melatonin replacement therapy effectively improves sleep quality in this population.

Aged↗
PubMed1995

Modulation by melatonin of protein secretion from melanoma cells: is cAMP involved?

The pineal hormone melatonin modulates constitutive protein secretion from melanoma M2R cells. Nanomolar concentrations of melatonin inhibited protein secretion early after plating or at low cell density, but facilitated it late after plating or at high cell density. Inhibition by melatonin of adenylate cyclase is the best known downstream response to melatonin. We have therefore examined the involvement of cAMP in the melatonin-mediated modulation of protein secretion from the melanoma cells. Melatonin slightly but significantly reduced cell cAMP content when effecting inhibition and marginally increased cAMP levels when effecting facilitation of protein secretion. Dibutyryl cAMP abrogated the melatonin-mediated inhibition but not facilitation of protein secretion without affecting basal secretion. Accordingly, forskolin prevented the inhibitory action of melatonin on protein secretion without affecting basal secretion. The selective protein kinase A inhibitor H-89 did not alter the inhibitory effect of melatonin at low cell density and slightly facilitated secretion at high cell density with or without melatonin. Thus, melatonin's effects on protein secretion may not be mediated via cAMP. Nevertheless, changes in cAMP or protein kinase A activity can abrogate, or mask, the melatonin-mediated responses.

Animals↗
PubMed1995

Effects of long-term administration of melatonin and a putative antagonist on the ageing rat.

Adult rats were treated with either melatonin, the putative melatonin antagonist N-(2,4 dinitrophenyl)-5-methoxytryptamine (ML-23), their combination, or a vehicle for 16 months via the drinking water. The survival rates, serum testosterone and densities of 125I-melatonin binding sites in the medulla-pons and hypothalamus of the animals at the age of 27-29 months were significantly higher in the melatonin than vehicle-treated group. Surprisingly, ML-23 without or with melatonin, also prolonged the life-span of the aged animals. ML-23 treatment greatly increased 125I-melatonin binding in the medulla-pons whereas this increase was prevented by melatonin supplementation. Thus melatonin can attenuate age-related decrease in survival rates, testosterone and brain 125I-melatonin binding sites, while chronic blockade by the putative antagonist also elicits melatonin-mimetic responses, perhaps by effecting supersensitivity.

5-Methoxytryptamine↗
PubMed1995

High-affinity binding of melatonin to hemoglobin.

Determination of melatonin by radioimmunoassay in plasma samples from hemolyzed blood often yields flawed values. We studied the possibility that hemoglobin can bind melatonin and the iodinated tracer 125I-melatonin. The specific binding of 125I-melatonin to purified bovine hemoglobin was found to be rapid, saturable, and reversible (Kd = 315 pM, Bmax = 58 pmol/mg protein) and was inhibited by 2-iodomelatonin, serotonin, melatonin, and 5-methoxytryptamine. These data are compatible with the concept that hemoglobin can interfere with melatonin determinations by competing for melatonin and the iodinated tracer. Unlike melatonin receptor binding, the binding of 125I-melatonin to hemoglobin was not inhibited by guanine nucleotide analogs (i.e., GTP gamma S, GTP beta S, and Gpp(NH)p). Sodium cyanide had no effect on 125I-melatonin binding, indicating that 125I-melatonin does not bind to the heme group. On the other hand, 2,3-bisphosphoglycerate, at physiological concentrations (3-4 mM), decreased the apparent Bmax and Kd of 125I-melatonin binding to hemoglobin. These data suggest that 125I-melatonin binding to hemoglobin is conformation-specific and is unfavorable in the deoxyhemoglobin state. Hemoglobin may serve as a carrier protein for melatonin in the blood and discharge it in the target organs. Subsequently, the efficacy of melatonin's action as a hormone or antioxidant in target tissues may be enhanced.

2,3-Diphosphoglycerate↗
PubMed1995

Oxygen consumption and body temperature rhythms in the golden spiny mouse: responses to changes in day length.

The golden spiny mouse Acomys russatus is a rock dwelling rodent which lives in extremely arid and hot habitats. In Israel it is nocturnal except in areas in which it coexists with the common spiny mouse A. cahirinus. In such places it is diurnal. The daily rhythms of body temperature (Tb) and oxygen consumption (VO2) were compared in mice acclimated to two different photoperiod regimes in the laboratory: 8L:16D (short day) and 16L:8D (long day) at a constant ambient temperature. The daily rhythms of VO2 and of Tb in A. russatus were found to differ greatly under long and short photoperiod. Both parameters peaked at lights-out under both photoperiod regimes. In short day acclimated mice the effect of transmitter implantation was also studied. VO2 values at night were lower after implanting. The results of this study show that Tb and VO2 rhythms are altered by the lighting regimes. Seasonal acclimatization of thermoregulatory mechanisms in the golden spiny mouse are partly induced by changes in photoperiodicity.

Acclimatization↗
PubMed1995

Facilitation and inhibition of G-protein regulated protein secretion by melatonin.

Melatonin has been found to inhibit or enhance the constitutive secretion of proteins from the cultured melanoma cells at nanomolar concentrations (0.5-10 nM), in a dose dependent manner. The amplitude and direction of the response were found to depend on cell density: melatonin inhibited the release early after plating or at low cell density, but facilitated the release later on, or at high cell density. To elucidate the involvement of G-proteins in these responses, the effects of guanosine 5'-O-(3-thiotriphosphate) (GTP tau S; which was introduced into the cells during the process of permeabilization and resealing with ATP), aluminum fluoride, pertussis and cholera toxins on protein secretion from the cells were assessed in the absence and presence of melatonin. At low cell density, melatonin inhibited release, but paradoxically enhanced it when GTP hydrolysis was blocked (by GTP tau S or cholera toxin treatment). Aluminum fluoride and melatonin inhibited protein release in the absence or presence of GTP tau S. At high cell density, melatonin facilitated the release and so did GTP tau S, aluminum fluoride, their combination, and cholera toxin treatment. However, in the presence of the combination of GTP tau S, aluminium fluoride and melatonin, protein release was paradoxically inhibited. Similar treatment of the cells with pertussis toxin, did not affect the melatonin-mediated inhibition or facilitation. These results indicate that the effects of melatonin on protein secretion are mediated by at least one heterotrimeric G protein which belongs to the Gs class. In addition, melatonin can facilitate secretion via a cholera and pertussis toxins-insensitive mechanism which can be inhibited by aluminum fluoride. This effect is manifested when Gs is permanently activated (by GTP tau S or cholera toxin).

Aluminum Compounds↗
PubMed1995

Melatonin replacement therapy of elderly insomniacs.

Changes in sleep-wake patterns are among the hallmarks of biological aging. Previously, we reported that impaired melatonin secretion is associated with sleep disorders in old age. In this study we investigated the effects of melatonin replacement therapy on melatonin-deficient elderly insomniacs. The study comprised a running-in, no-treatment period and four experimental periods. During the second, third and fourth periods, subjects were administered tablets for 7 consecutive days, 2 hours before desired bedtime. The tablets were either 2 mg melatonin administered as sustained-release or fast-release formulations, or an identical-looking placebo. The fifth period, which concluded the study, was a 2-month period of daily administration of 1 mg sustained-release melatonin 2 hours before desired bedtime. During each of these five experimental periods, sleep-wake patterns were monitored by wrist-worn actigraphs. Analysis of the first three 1-week periods revealed that a 1-week treatment with 2 mg sustained-release melatonin was effective for sleep maintenance (i.e. sleep efficiency and activity level) of elderly insomniacs, while sleep initiation was improved by the fast-release melatonin treatment. Sleep maintenance and initiation were further improved following the 2-month 1-mg sustained-release melatonin treatment, indicating that tolerance had not developed. After cessation of treatment, sleep quality deteriorated. Our findings suggest that for melatonin-deficient elderly insomniacs, melatonin replacement therapy may be beneficial in the initiation and maintenance of sleep.

Aged↗
PubMed1992

Modification by oxazepam of the diurnal variations in brain 125I-melatonin binding sites in sham-operated and pinealectomized rats.

Sham-operated and pinealectomized male rats were maintained at 14 h light:10 h dark cycles (lights-on 5.00 h) and injected daily, for 14 days, with oxazepam or vehicle. 125I-melatonin binding was recorded in synaptosomes prepared at 10.00, 18.00, and 24.00 h from the hypothalamus, hippocampus and medulla-pons of the rats. In the sham-operated, vehicle treated rats, specific 125I-melatonin binding in all brain areas studied was higher at 18.00 h, whereas in the oxazepam-treated animals, binding was higher at 24.00 h than at the other times tested. In the pinealectomized, vehicle-treated rats, the binding recorded at 18.00 h in all three brain areas, was lower than at the other times of day tested. Oxazepam treatment decreased 125I-melatonin binding at 24.00 h in the hippocampus and medulla-pons of the pinealectomized rats and did not significantly affect the binding in the hypothalamus. These results indicate the ability of oxazepam, pinealectomy and their combination, to manipulate the diurnal variations in 125I-melatonin binding sites in the rat brain.

Animals↗
PubMed1991

Melatonin binding proteins identified in the rat brain by affinity labeling.

N-Bromoacetyl-2-iodo-5-methoxytryptamine (BIM), a novel derivative of the biologically active melatonin analog, 2-iodomelatonin, was prepared and used to identify melatonin binding proteins in rat brain synaptosomes. Incubation of the synaptosomes with BIM resulted in a time and concentration dependent, irreversible inhibition of 2-[125I]iodomelatonin binding. In parallel, the radioactive form of BIM, N-bromoacetyl-2-[125I]iodo-5-methoxytryptamine ([125I]BIM) became incorporated into the synaptosomes. The incorporation of [125I]BIM was inhibited by BIM, 2-iodomelatonin and melatonin but not by 5-methoxytryptamine or N-acetyl serotonin. [125I]BIM became covalently attached to three polypeptides with apparent molecular weight values of 92, 55 and 45 kDa; the labeling of all three proteins was markedly inhibited by melatonin. These results indicate that the 92, 55 and 45 kDa polypeptides are melatonin binding proteins.

Affinity Labels↗
PubMed1991

Affinity labeling of melatonin binding sites in the hamster brain.

N-Bromoacetyl-2-iodo-5-methoxytryptamine (BIM), a novel derivative of the biologically active melatonin analog, 2-iodomelatonin, was used to identify melatonin binding proteins in synaptosomes from Syrian hamster brain. Incubation of the synaptosomes with BIM resulted in a concentration dependent, irreversible inhibition of 2-125I-iodomelatonin binding. The radioactive form of BIM, N-Bromoacetyl-2-125I-iodo-5-methoxytryptamine (125I-BIM), became covalently attached to three proteins in the synaptosomes, in a concentration dependent manner. These proteins had apparent molecular weight values of 92, 55 and 45 kilodaltons. The incorporation of 125I-BIM into all three proteins was inhibited by BIM greater than 2-iodomelatonin greater than melatonin whereas the melatonin antagonist N-(1,4 dinitrophenyl)- 5-methoxytryptamine (ML-23) selectively inhibited the labeling of the 45 kDa protein. These results indicate that the 92, 55 and 45 KDa polypeptides are melatonin binding proteins.

5-Methoxytryptamine↗
PubMed1991

Castration affects brain iodomelatonin binding in hamsters maintained in long but not short days.

The effects of castration on 2-[125I]iodomelatonin ([125I]melatonin) binding sites in discrete brain areas were investigated in male Syrian hamsters exposed to long and short days. In hamsters maintained in long days (14 h light: 10 h darkness), castration produced a marked decrease in [125I]melatonin binding in the brain, particularly in the medulla-pons hypothalamus and hippocampus. Maximal response in the medulla-pons and hypothalamus was observed at 3 days; specific [125I]melatonin binding subsequently increased to reach control levels within 30 days after castration. In the hippocampus, the decrease in [125I]melatonin binding was still evident at 90 days after castration and could be reversed by testosterone. Exposure to short days (8 h light: 16 h darkness) did not affect [125I]melatonin binding in the various brain areas of the intact hamsters; even after 90 days when circulating testosterone decreased to castrated levels, the binding remained as in intact, long-day-housed controls. Moreover, [125I]melatonin binding in the various brain areas of hamsters exposed to short days was unaffected by castration. The results clearly indicate that the regulation by testosterone of melatonin receptors in the medulla-pons, hypothalamus and hippocampus of the male hamster depends on the prevailing photoperiod.

Animals↗
PubMed1989

Diurnal variations in melatonin binding sites in the hamster brain: impact of melatonin.

The distribution of 125I-melatonin binding sites in the male Syrian hamster brain was recorded at 3 times over a 24 h period. The binding in the hypothalamus, hippocampus, medulla-pons and midbrain of the hamsters varied significantly over the 24 h period with different patterns and phases. No such variations were observed in the parietal cortex. Daily morning (10.00 h) or late afternoon (18.00 h) injections of melatonin for 28 days markedly increased the serum concentrations of melatonin at all times recorded. Serum concentrations of testosterone were significantly lower in animals injected with melatonin in the late afternoon than in the untreated controls; no such decrease was observed in animals injected in the morning despite the continuously elevated levels of circulating melatonin. The daily melatonin injections did not significantly affect 125I-melatonin binding in the hypothalamus, parietal cortex and medulla-pons. In the midbrain, 125I-melatonin binding decreased regardless of the time of injection. In the hippocampus, morning melatonin injections caused a marked decrease in 125I-melatonin binding at all times recorded whereas melatonin injected in the late afternoon led to a decrease in 125I-melatonin binding at 10.00 h only. These results indicate diurnal variations in 125I-melatonin binding sites in discrete brain areas of the golden hamster, persisting despite prolonged duration of elevated levels of circulating melatonin. The differential effects of timed melatonin injections on the hippocampal 125I-melatonin binding sites are positively correlated with the counter-antigonadal response produced by morning melatonin injections.

Animals↗
PubMed1989

A novel melatonin antagonist, N-(2,4-dinitrophenyl)-5-methoxytryptamine neutralizes some effects of melatonin in the female Syrian hamster.

In this present study we evaluated the ability of a recently synthesized melatonin antagonist, N-(2,4-dinitrophenyl)-5-methoxytryptamine (ML-23), to antagonize the effects of afternoon injections of melatonin on the reproductive and thyroid axes in the female Syrian hamster. Thirty-six animals were divided into four groups and treated daily for 13 weeks with an afternoon injection of melatonin (25 micrograms/injection) or saline diluent. ML-23 was given via the drinking water to both melatonin- and saline-treated groups. The experiment was continued until 78% of melatonin-treated animals exhibited acyclicity. The results show that ML-23 partially reversed the effects of melatonin on pituitary follicle-stimulating hormone concentrations but was without effect on the decreased pituitary and plasma prolactin concentrations induced by melatonin treatment. Furthermore, ML-23 antagonized the effects of melatonin on plasma thyroxine levels and significantly increased plasma triiodothyronine concentrations and the free triiodothyronine index when used in combination with melatonin. The decrease in ovarian weight and plasma estradiol, but not progesterone, obtained with melatonin treatment also was reversed by ML-23. Our data suggest that ML-23 prevents the effects of melatonin treatment on ovarian weight, pituitary follicle-stimulating hormone levels, plasma estradiol, and thyroxine concentrations in the female Syrian hamster. Since ML-23 did not prevent the effects of melatonin on pituitary weight, plasma luteinizing hormone and prolactin, and pituitary prolactin concentrations, the actions of ML-23 may involve only peripheral sites of action of melatonin. Alternatively, the dose of ML-23 may not have been optimal to prevent all of the central effects of the indoleamine.

5-Methoxytryptamine↗