摘要:

Human pineal glands obtained from 77 post‐mortem sources from various age groups and times of death were used to examine the 24‐hour cycle of serotonin (5‐HT), melatonin, N‐acetylserotonin (NAS), and beta adrenoceptor density. Pineal glands were divided sagitally and a single half was used to measure 5‐HT, NAS, and melatonin concentrations, while the remaining half from the same gland was employed to assess changes in the density of beta adrenoceptors on partially purified membranes. The results show that density of pineal beta adrenoceptors was relatively constant between midnight and 18.00 h and became significantly higher between 18.00 and 20.00 h as measured by ligand saturation binding experiments using (125‐1) iodocyanopindolol. The receptor affinity of all of the samples assayed remained in relatively narrow range near 58 pM and only changes in the relative receptor density were apparent. The up‐regulation of receptors coincided with an increase in the concentration of 5‐HT that began to rise between 16.00 and 20.00 h and became maximal between 20.00 and midnight. NAS, the immediate precursor of melatonin, was also at maximal levels between 20.00 h and midnight. Both 5‐HT and NAS began declining after midnight and this change corresponded to the maximal pineal gland concentration of melatonin between midnight and 4.00 h. It is therefore suggested that the up‐regulation of beta adrenoceptors noted during the late afternoon and early evening hours corresponds to the increased synthesis of 5‐HT and the subsequent conversion to NAS. These events are followed by the highest accumulation of melatonin after midnight and represent the synthesis of melatonin from its precursor NAS in

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00688.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

This study examined plasma melatonin levels and the suppressant effect of light on melatonin production in the squirrel monkey. Monkeys were maintained on a 12: 12 light‐dark cycle (LD 12: 12) with lights on from 07:00 to 19:00. Plasma levels of melatonin were determined by gas chromatography negative chemical ionization mass spectrometry. Melatonin levels at 00:00 (99.5 ± 18.9 pg/ml) were significantly higher than at 02:00 (57.21 ± 7.7 pg/ml; Student's t = 2.859;P≤ 0.021). Baseline values at 02:00 were compared with levels at the same time of day after exposure to 2 hours of 200 lux of light (30.6 ± 13.1 pg/ml), which caused an average suppression of 54.8% in melatonin levels. One animal did not show light suppression. Results indicated that the squirrel monkey suppressant response to light, as well as baseline values of melatonin, varied between a

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00689.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The nocturnal peak in pineal and serum melatonin content was reduced following administration of the selective alpha‐1 adrenoceptor antagonist prazosin in a dose of 0.25 mg/kg. The effect was pronounced one hour post treatment during the late dark phase of the daily photocycle. These data confirm the reported findings that the hamster pineal sensitivity to adrenergic challenge is confined to the second part of the dark phase and indicate that postsynaptically located alpha‐1 adrenoceptors are also involved in the physiological control of melatonin synthesis and/or release in that spec

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00690.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Recent studies from our laboratories have shown that the bovine pineal gland contains a muscarinic cholinergic receptor with a Kdvalue of 0.423 ± 0.010 nM and a Bmaxvalue of 69.75 ± 20.91 fmol/mg protein. In order to substantiate further the possible existence of a pineal cholinergic transmission, we have measured the activity of choline acetyltransferase and delineated its kinetic properties in the bovine pineal gland. This enzyme exhibited an activity of 0.0339 ± 0.0042 nmol/mg protein/min. Furthermore, the bovine pineal choline acetyltransferase possessed a Km, value of 124.86 ± 24.06 μM and a Vmaxvalue of 0.0598 ± 0.0034 nmol/mg protein/min for acetyl CoA, and a Kmvalue of 3.11 ± 0.94 mM and a Vmaxvalue of 0.0155 ± 0.0016 nmol/mg protein/min for choline. The presence of muscarinic cholinergic receptors along with a specific choline acetyltransferase are supportive evidences that the bovine pineal gland may receive cholinergic inne

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00691.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00692.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of35S‐methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10: 00 or 18: 00. Injection of 100 μg/kg of melatonin for ten days at either time induced a significant depression in the incorporation of35S‐methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 μg/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot‐blot analysis, decreased only after the injection of 100 μg/kg melatonin for ten days at 10:00. Neither a 10‐μg/kg dose of melatonin, nor a single injection of 100 μg/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 μg/kg for ten days) did not modify hypothalamic somatostatin or H‐Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00693.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Free amino acids and indoles were measured by HPLC in single pineal glands of 5‐, 10‐and 20‐day‐old rats sacrificed during mid‐light and mid‐dark at each age. Melatonin was detectable in neonates (5‐day‐old), but day vs night differences in indole constituents did not occur until 10 days of age. Free amino acid steady state levels were high in neonates and there was a tendency for reversal of day vs night differences coinciding with the onset of circadian rhythmicity in indole biosynthesis. High correlations (r>0.85) existed for taurine vs. glutamate in individual glands regardless of age and time of sacrifice. These findings suggest that taurine and glutamate are biochemically interrelated and that developmental changes in amino acid metabolic pools reflect functional innervati

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00694.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Male Syrian hamsters were exposed to short photoperiods (10L: 14D) for ten weeks and received daily ethanolic saline (1:10), propranolol (125 μg, sc) or melatonin (25 μg, sc) injections at 16: 45. Some hamsters also received melatonin implants (1 mg in 24 mg beeswax, sc) every two weeks in addition to the above treatments. Testicular weights were determined at the beginning, every three weeks, and at the end of the experiment. Serum hormone levels, hypothalamic amine levels and cortical amine levels were also determined at the conclusion of the experiment. Propranolol prevented the decline in testes weight produced by short photoperiod (P<0.001 versus control). Propranolol was not able to prevent daily injections of melatonin from producing gonadal regression. Melatonin implants blocked testicular regression produced by both short photoperiod and melatonin injections. No differences in hypothalamic or cortical amine levels were observed between the treatment groups. These results add further support to the suggestion that propranolol is acting at the pineal gland preventing melatonin synthesis and not at a post‐pineal central site which would affect melatonin binding and act

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00695.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

We have studied the pattern of variations in extent of thymidine incorporation during pulse‐labelling in cultured chick pineal glands. During the first 24‐30 h in culture the extent of pulse‐labelling varied in parallel with the cycle in cumulative incorporation. Pulse‐labelling was seen during the period of apparent arrest of cumulative incorporation. However, it was probably “masked” by the SD of assays of cumulative incorporation and represented a minor, but distinct, process of thymidine incorporation. The pattern of variation in extent of pulse‐labelling was qualitatively consistent under a wide variety of conditions. Control of this pattern appeared to be different from that of the circadian rhythm in cumulative thymidine

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1990.tb00696.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY