摘要:

Abstract:Besides its presence in the pineal gland, melatonin has been found in a variety of other tissues as well. The indoleamine also has been identified in invertebrates including an unicellular organism where it exhibits a diurnal rhythm. Although melatonin is mainly known for its effects on seasonal reproduction and endocrine physiology, there is evidence showing that this ubiquitously acting hormone is also a potent free radical scavenger, thereby providing protection from oxidative attack to DNA and other biomolecules. Through the years, melatonin was thought to be exclusively cytosolic. However, careful examination of some of these pioneering reports revealed a nuclear localization of melatonin in different tissues including the retina and Harderian glands. Using a very sensitive immunocytochemical method, we have also found that melatonin is located in the nucleus of many cells where it may bind to nuclear components. The use of cell fractionation studies followed by radioimmunoassay confirmed these results. The administration of exogenous melatonin resulted in a marked increase in the nuclear melatonin content without a concomitant change in the cytosolic fraction. In addition to its ability to scavenge free radicals, its location in the nucleus suggests possible genomic actions.

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00511.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Experiments were conducted to determine if a correlation exists between any aspect of the pineal melatonin rhythm (such as its duration or phase) in the lizardAnolis carolinensisand the reproductive response to photoperiod. The rhythm of pineal melatonin content was determined in anoles exposed to nightbreak lighting protocols (10L:5D:1L:8D, 10L:10D:1L:3D), resonance lighting cycles (LD 11:13, LD 11:25), and T‐cycle lighting protocols (LD 11:7, LD 11:9, LD 11:13, LD 11:15, LD 11:19) and compared with the testicular response to these lighting protocols as determined previously [Underwood and Hyde, (1990) J. Comp. Physiol. (A) 167:231–243]. Different T‐cycles and nightbreak cycles elicited changes in both the duration of the melatonin peak and the phase of the melatonin peak relative to these light cycles. The response to the resonance cycle (LD 11:25) was complex, probably due to the overlapping patterns of two groups whose pineal melatonin rhythms were entrained approximately 12 hr out of phase with each other. No correlation was observed between the duration, or the amplitude, of the nocturnal melatonin peaks seen on the various light cycles and the reproductive response to these cycles. A correlation was observed between the phase of the pineal melatonin rhythm and the reproductive response. Light cycles were inductive (stimulated testicular growth) when the entrained melatonin rhythm peaked near the light‐to‐dark or the dark‐to‐light transition, but they were not inductive when the melatonin rhythm peaked during the middle third of the night. These results suggest that if melatonin is involved in the transduction of photoperiodic information inAnolis, neither the duration nor amplitude of the nocturnal melatonin pulse is involved in the measurement of day length. Instead, the phase‐relationship of the melatonin rhythm to the rest of the circadian system may determine photoperiodic

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00512.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Exposure of adult rat pineal glands in organ culture to the polypeptides vasoactive intestinal polypeptide (VIP), and peptide N‐terminal histidine C‐terminal isoleucine (PHI) increases pineal serotonin N‐acetyltransferase (NAT) activity and melatonin synthesis. The following research results are taken to indicate that VIP and PHI share common components of the NAT induction system: (1) The effects of the two peptides are additive at concentrations of 10 nM VIP and 100 nM PHI but not at higher peptide concentrations. (2) Pineals from newborns also respond to PHI with a dose dependent increase in NAT activity. NAT responses are additive at the same concentrations as seen with the adult pineals. (3) Light exposure affects the sensitivity of pineals to VIP and PHI stimulation in a similar manner; pineals taken after 3 hr of light are much less sensitive to PHI or VIP than those taken after 13 hr of light. (4) Pineals exposed for 48 hr to either PHI or VIP have a reduced NAT response to either agonist, which is reversible by culture in agonist‐free media. (5) Neither VIP nor PHI stimulation of NAT activity is affected by concentrations of the VIP antagonists (N‐Ac‐Tyr1, D‐Phe2)‐GRF(l‐29)‐NH2 (NAcTDGRF), L‐8‐K, VIP‐Neurotensin Hybrid (VIPNET), or (4Cl‐D‐Phe6, Leu17)‐VIP (4C1PLVIP), which affect VIP bindi

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00513.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:A new procedure with the G280 antibody of Kennaway provides an assay for circulating melatonin (aMT) with a sample volume (200 μl), an analytic (0.33 pg/ml) and functional (0.62–0.80 pg/ml) detectability, a 50% displacement dose (6.4 pg/ml), a Kd (0.657 pM), and measured circulating daytime levels lower than reported for previous procedures, and 100% assay recovery. The normal daytime range in adult human and Syrian hamster serum was 0.4–4 pg/ml. The pattern of fall of the nocturnal surge of Syrian hamster serum aMT near the time of lights‐on was unaltered by extended darkness. Isoproterenol (ISO) injection 1 hr after lights‐on, when aMT had reached daytime levels, raised serum and pineal aMT dramatically 2 hr postinjection. The same dose of ISO injected 4 hr into light produced only a small detectable increase. Novel extension of nocturnal darkness did not affect the responses to ISO. Thus, when they are allowed to occur at the usual time on a 10‐hr dark schedule, both the fall from the nocturnal aMT surge and the subsequent loss of pineal beta‐adrenergic responsiveness in this species occur endogenously (probably entrained) rather than from gating by acute effects of morning light. Changes in daytime serum aMT consistent with concomitant changes in the pineal can be measured with a sufficiently sensitive radi

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00514.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:This study examined the effects of two novel melatonin analogues in adult Djungarian hamsters housed under long photoperiod (LD 16:8). Daily injection (10 μg, s.c.) of either melatonin, 5‐methoxy N‐butanoyltryptamine (bMT), or 5‐methyl N‐butanoyltryptamine (5‐MebT) 3 hr before lights off for 8 weeks led to a significant decrease in paired testis weight compared to vehicle‐injected controls. The reduction in testis weight was of similar magnitude with melatonin and bMT, but 5‐MebT was not as effective. The affinity of the analogues was determined in competition experiments using chicken brain membranes and 2‐[125I]iodomelatonin (2‐[125I]aMT). Replacing the N‐acetyl side‐chain of melatonin with an N‐butanoyl group increased affinity for the chicken brain 2‐[125I]aMT binding site, but exchanging the 5‐methoxy group of melatonin for a 5‐methyl group reduced affinity. These studies show that these analogues not only inhibit 2‐[125I]aMT binding in vitro but also mimic melatoni

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00515.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Opioid binding sites in the bovine pineal were characterized using the highly selective delta opioid agonist3H‐[D‐Pen2, pCl‐Phe4, D‐Pen5] enkephalin (DPDP(Cl)E). Pineal membranes possess a single class of high affinity binding sites for this delta ligand (Kd= 0.26 nM; Bmax= 250 fmol/mg protein). The specific opioid antagonist naloxone dose dependently inhibited3H‐DPDP(C1)E binding, confirming that this ligand is indeed binding to opioid receptors. The delta selective ligands deltorphin and [D‐Pen2,5] enkephalin (DPDPE) were much more potent than the mu selective compounds dermorphin and [D‐Ala2, MePhe4Gly5‐ol]enkephalin (DAMGO) in inhibiting3H‐DPDP(Cl)E binding. These results demonstrate that in bovine pineal membranes, DPDP(Cl)E binds to delta opioid sites. Autoradiographic studies showed a uniform distribution of3H‐DPDP(Cl)E binding over the bovine pineal in the sections we analyzed. This distribution suggests that delta opioid binding sites are associated with pinealocytes which account for the majority of cell types in the pineal. However, it is not possible to rule out that these receptors may also be associated with other cell types which are present in the bovine pineal. The density and widespread distribution of delta opioid receptors supports the hypothesis that endogenous opioid peptides directly modul

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00516.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY