摘要:

Huerto‐Delgadillo L, Antón‐Tay F, Benítez‐King G. Effects of melatonin on microtubule assembly depend on hormone concentration: rate of melatonin as a calmodulin antagonist. J. Pineal Res. 1994: 17: 55–62. ©Munksgaard, 1994AbstractMelatonin may play a key role in cytoskeletal rearrangements through its calmodulin antagonism. In the present work, we tested this hypothesis by studying melatonin effects on both microtubule polymerization in vitro and cytoskeletons in situ. Microtubule assembly is a dynamic process inhibited by Ca2+/calmodulin. Calmodulin antagonists prevent the inhibition by binding to Ca2+‐activated calmodulin, thus causing microtubule enlargement. In the presence of calmodulin (5 μM) and CaCl2(1 mM), polymerization at equilibrium was inhibited by 40%. Complete reversal of the Ca2+/calmodulin effect on microtubules was observed with 10‐9M melatonin or with 10‐5M trifluoperazine or 1 μg/ml of compound 48/80. In the absence of Ca2+/calmodulin, melatonin at 10‐5M inhibited tubulin polymerization like 10‐4M trifluoperazine does. Melatonin effects on microtubule assembly at both nanomolar and micromolar ranges were corroborated in cytoskeletons in situ. Therefore, it is suggested that at a low concentration (10‐9M), cytoskeletal melatonin effects are mediated by its antagonism to Ca2+/calmodulin. At a higher concentration (10‐5M), non‐specific binding of melatonin to tubulin occurs, thus overcoming the melatonin antgonism to Ca2+/calmodulin. The results support the hypothesis that under physiological conditions, melatonin synchronizes different body rhythms through cytoskeletal rearrangements mediated

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00114.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Zawilska JB. Clonidine in vivo mimics the acute suppressive but not the phase‐shifting effects of light on circadian rhythm of serotonin N‐acetyltransferase activity in chick pineal gland. J. Pineal Res. 1994; 17: 63–68. ©Munksgaard, 1994AbstractComparative in vivo studies on effects of pulses of light and clonidine, a selective agonist of α2‐adrenergic receptors, on the circadian rhythm of serotonin N‐acetyltransferase (NAT) activity in chick pineal gland were performed. Six‐hour pulses of white light caused an acute suppression of the nocturnal NAT activity and phase‐dependent phase shifts of the circadian rhythm of the enzyme activity relative to controls. Systemic administration of clonidine acutely suppressed NAT activity of chick pineal gland, but did not affect the phase of subsequent cycles in constant darkness. These results give further support to the concept based on in vitro studies that α2‐adrenergic receptors are involved in regulation of melatonin biosynthesis in chick pineal gland by a mechanism distal to the pacemaker that generates the circadia

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00115.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Meissl H, Yáñez J, Ekström P, Grossman E. Benzodiazepines influence melatonin secretion of the pineal organ of the trout in vitro. J. Pineal Res. 1994; 17: 69–78. ©Munksgaard, 1994AbstractThe effect of benzodiazepines (BZP) on melatonin release was investigated in the pineal gland of the rainbow trout,Oncorhynchus mykiss, maintained under in vitro perifusion culture conditions. Melatonin and the methoxyindoles 5‐methoxytryptophol (5‐MTOL), 5‐methoxyindoleacetic acid (5‐MIAA), and 5‐methoxytryptamine (5‐MT) were determined directly in samples of the supervision medium by HPLC with electrochemical detection. Melatonin release was significantly increased by addition of diazepam and clonazepam in a dose‐related and reversible manner. The effects of benzodiazepines were more pronounced in light‐adapted pineal organs, when melatonin secretion is low, than under scotopic conditions. When the perifusion medium was replaced by a medium containing low calcium, high magnesium concentrations, melatonin release was considerably decreased by 70% in light‐adapted and 20% in dark‐adapted pineal organs. Addition of diazepam to low Ca2+, high Mg2+‐medium reversed the decrease of melatonin release and produced a clear rise in its secretion rate. Addition of the BZP antagonist flumazenil to the perifusion medium slightly decreased melatonin release in the light‐ and dark‐adapted state, whereas the peripheral receptor antagonist PK 11195 did not alter melatonin release. The effect of diazepam is reduced by simultaneous addition of flumazenil to the superfusion medium, suggesting that the effects of diazepam are receptor‐mediated. The methoxyindoles 5‐MTOL, 5‐MIAA, and 5‐MT showed no significant changes of their release pattern after diazepam application in light‐ and dark‐adapted pineal organs. These results suggest that BZP can influence melatonin production and release by an intrapineal action possibly on th

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00116.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Benouali‐Pellisier S. Melatonin is involved in cholecystokinin‐induced changes of ileal motility in rats. J. Pineal Res. 1994: 17: 79–85. ©Munksgaard 1994AbstractThe aim of this study was to determine, in the rat, the interaction between melatonin and cholecystokinin in the regulation of the ileal interdigestive motility. This was analyzed by the chronic electromyography technique. Ileal motility was defined by the presence of intermittent spike bursts corresponding to the contractile activity of the organe. In control rats, these spike bursts were organized in cyclic myoelectrical complexes. Each complex is characterized by two successive spiking activity phases: the irregular phase (ISA) followed by the regular phase (RSA). Pinealectomy suppressed the RSA phase so ileal motility was constituted only by the ISA phase. When melatonin (1 mg/kg i. v.) was injected into pinealectomized rats, RSA phases were immediately and definitively restored. RSA phases were also re‐established when the “alimentary” type of cholecystokinin receptors (CCKA) were blocked by selective antagonists such as L364,718 or SR27897 (1 mg/kg i. v.). The latter had better brain accessibility than L364,718. Unlike the effects of melatonin, the effect of these antagonists was neither immediate (the latency is longer for L364,718 than for SR27897) nor definitive. In control rats, cholecystokinin (5 |μg/kg i. v.) induced a characteristic long‐lasting (29 |Mp 2 min) excitomotor effect on the ileum. This effect was suppressed in pinealectomized rats and was restored after melatonin treatment. These results suggest that, via the central nervous system, melatonin is involved in the modulation of cholecystokinin action on

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00117.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Edmonds KE, Stetson MH. Photoperiod and melatonin affect testicular growth in the marsh rice rat (Orgzonys palustris). J. Pineal Res. 1994: 17: 86–93. ©Munksgaard 1994AbstractReproduction in rice rats is subject to photoperiodic control and the pineal gland mediates this effect. We examined the effects of the pineal gland hormone melatonin on testicular weight when administered via implants, injections, and infusions. Testicular weight was modified by photoperiod and the size of the melatonin implant. Twenty‐millimeter implants suppressed testicular weight in rice rats housed on 12‐ and 16‐hr photoperiods, while those housed on a 14‐hr photoperiod were more sensitive to melatonin; in these animals 10‐ and 20‐mm implants inhibited testicular weight. Melatonin implants also prevented rice rats from responding to a change in photoperiod with the appropriate alteration of testicular growth. Melatonin injections inhibited testicular growth when administered before lights out on LD 14: 10, but not on LD 16: 8. Morning injections had no effect on either photoperiod. Finally, 12‐hr duration melatonin infusions inhibited testicular growth in pinealectomized rice rats on LD 16: 8, while 6‐hr duration infusions were without effect. These data show that the pineal, through the secretion of melatonin, is a phototransducing organ intimately involved in testicular g

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00118.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Abe M, Reiter RJ, Orhii PB, Hara M, Poeggeler B. Inhibitory effect of melatonin on cataract formation in newborn rats: Evidence for an antioxidative role for melatonin. J. Pineal Res. 1994; 17: 94–100. ©Munksgaard 1994AbstractWe evaluated the inhibitory effect of melatonin, a recently discovered scavenger of free radicals, on cataract formation in the newborn rat. The glutathione synthesis inhibitor, buthionine sulfoximine (BSO) (3 mmol/kg), was intraperitoneally injected into newborn rats for 3 consecutive days starting on day 2 after birth. These glutathione depleted rats develop cataracts. Melatonin (4 mg/kg) was injected intraperitoneally into half of the rats once a day beginning at day 2 after birth; the other half of the animals received solvent daily. The incidence of cataract was observed on day 16, after the eyes of the newborn animals had opened. Both reduced glutathione (GSH) and oxidized glutathione (GSSG) levels were measured. Cataracts were observed in all animals (18/18) treated with BSO plus solvent. The incidence of the cataract in the animals cotreated with melatonin was only 6. 2% (1/15). Total lenticular glutathione (GSH + GSSG) levels in BSO only treated rats were reduced by 97%. The total glutathione in the lens of the BSO plus melatonin group was significantly higher (by 3%) than that of the BSO only group. The percentage of the total glutathione as GSSG for the BSO plus solvent group was higher than the control value. Cotreatment of BSO injected rats with melatonin (4 mg/kg/day) clearly reduced cataract formation proving that it is directly or indirectly protective against oxidative stress which accompanies glutathione deficiency. The inhibitory effects of melatonin on cataract formation in this study could be due to melatonin's free radical scavenging activity or due to its stimulatory effect on glutathione producti

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00119.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY