摘要:

Paterson AM, Foldes A. Melatonin and farm animals: Endogenous rhythms and exogenous applications. J. Pineal Res. 1994:16:167–177.AbstractStudies on farm animals have contributed significantly to our increased understanding of basic melatonin‐related physiological mechanisms, as well as to the regulation of reproduction and pelage in individual domestic species. This review concentrates on recent work on the role of melatonin in the regulation of porcine reproduction, cervine endocrine, and behavioral cycles and wool and cashmere production which has added to this knowledge base. Early studies of the domestic pig indicated that melatonin secretion in this species differed markedly from that in other domestic and laboratory animals. There is now clear evidence that this is not the case and that the domestic pig uses a circadian rhythm of melatonin release for the transduction of photoperiodic information. Apparent inconsistencies among reports may be due, in part, to differences in the conditions under which the experiments were performed and to the assay systems employed to measure circulating melatonin, the concentrations of which are much lower than in other domestic species. Appropriately administered exogenous melatonin advances the onset of puberty in gilts, and may prove to be effective in overcoming seasonal infertility in female pigs. Appropriately timed melatonin and/or photoperiod treatments, administered to ruminants in utero, influence the reproductive physiology of the offspring, indicating that even in species which don't develop an endogenous melatonin rhythm till some weeks postnatally, awareness of photo environment, presumably via maternal melatonin, predates birth. Pre‐ or early postnatal melatonin‐related treatments also influence the development/cycle frequency of pelage. Areas requiring further investigation include the hormonal/growth factors involved, reasons for the transient nature of the effects in sheep and goats, and the reason for similar effects on pelage of augmenting or inactivating melatonin. Aspects of endogenous melatonin rhythms in farm species which require further study include: the significance of the abolition of the nocturnal melatonin peak in the sheep by prolonged short day exposure; the increased pineal bloodflow in sheep bred to produce high wool yields; the presence of high daytime melatonin levels immediately prior to the rut in the fallow buck; and the low amplitude of the rhythm in the domes

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00097.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Schmid HA, Requintina PJ, Oxenkrug GF, Sturner W. Calcium, calcification, and melatonin biosynthesis in the human pineal gland: A postmortem study into age‐related factors. J. Pineal Res. 1994:16:178–183.AbstractIt is believed that pineal calcification may be age‐associated and that the well‐demonstrated age‐related decline in melatonin biosynthesis may be an expression of an alteration in calcium homeostasis in the pinealocyte. Prior correlations of melatonin to calcium deposition and age were made on the basis of radiological or semiquantitative analysis. In this postmortem study of 33 subjects (age range 3 months to 65 years) calcium deposits measured by atomic absorption spectrometry correlated positively with age in day and night samples (day: r = 0.56, P<0.05; night: r = 0.818, P<0.001). Nighttime (2200 h to 0800 h) pineal melatonin content (HPLC fluorometry) was higher than daytime melatonin levels (nighttime 3.80 ± 0.3 vs. daytime 0.85 ± 0.4 ng/mg protein). Nighttime calcium levels in the supernatant correlated negatively with melatonin content (r =−

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00098.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Duncan MJ, Purvis CC. Effects of aging on photoperiodic responsiveness and specific 2‐[125I]‐iodomelatonin binding sites in the pars tuberalis and suprachiasmatic nuclei of Siberian hamsters. J. Pineal Res. 1994:16:184–187.AbstractSiberian hamsters undergo reproductive quiescence during exposure to a short day photoperiod, but this response appears to diminish with age. This study investigated whether age‐related losses in photoperiodic responsiveness may be related to decreases in specific 2‐[125I]‐iodomelatonin binding sites in the suprachiasmatic nuclei or pars tuberalis. Adult male Siberian hamsters (group 1: 3–6 months of age and group 2: 9–12 months of age) were exposed to short photoperiod (10 hr of light/day) for 10 weeks. Profound testicular regression was evident in the majority of the hamsters in group 1, but in only a few of the hamsters in group 2. There were no significant differences between the groups in the density or affinity of the specific 2‐[125I]‐iodomelatonin binding sites in either the suprachiasmatic nuclei or the pars tuberalis. These findings suggest that the failure of older hamsters to respond to short photoperiod is not caused by a loss of specific 2‐[125I]‐iodomelatonin binding sites in the suprachiasmatic n

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00099.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Walsh HA, Daya S, Whiteley CG. Mode of inhibition of rat liver tryptophan 2,3‐dioxygenase by melatonin. J. Pineal Res. 1994:16:188–192.AbstractLiver tryptophan 2,3‐dioxygenase is a cytosolic enzyme that plays a crucial role in the regulation of circulating levels of tryptophan. Stimulation of the activity of this enzyme by heme enhances the catabolism of tryptophan, making less tryptophan available for uptake into the brain. Melatonin, the major hormone of the pineal gland, is shown to cause competitive inhibition of this enzyme (Ki = 2. 70 μM). This structural analog of the substrate L‐tryptophan is a negative homotropic cooperative modulator of the enzyme. The enzyme has a Km = 100 μM, and the substrate concentration required for optimum activity was found to be 2. 5 mM with substrate inhibition becoming a feature at higher levels of t

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00100.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Bhagat L, Duraiswami S, Muralidhar K. Mode of action of inhibin‐like pineal antigonadotropin is different from melatonin during compensatory ovarian hypertrophy. J. Pineal Res. 1994:16:193–197.AbstractBoth melatonin and pineal antigonadotropic peptides have the same end effect, i. e., prevention of the hypertrophic response when tested in the conventional compensatory ovarian hypertrophy (COH) model. The present work was undertaken to study the effect of melatonin and a melatonin‐ and steroid‐free inhibin‐like ovine pineal antigonadotropin (PI) on serum follicle stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL) following hemiovariec‐tomy in adult Holtzman rats and also to ascertain if any similarity exists in their mode of action during COH. While melatonin prevented the transient rise in FSH at 12 hr after unilateral ovariectomy (ULO), thus retaining the basal preoperative level, PI depressed basal levels of FSH too. In addition, melatonin suppressed PRL and LH levels at 12 hr and 120 hr after ULO, respectively. PI, on the other hand, had no effect on serum LH and PRL levels. In light of our earlier in vitro results, which showed a direct inhibitory effect of PI and not of melatonin on pituitary FSH synthesis and release, the present results indicate a dichotomy in the mode of action of PI and melatonin. PI acts directly at the level of the pituitary while melatonin may act at the level of the hypothalamus or higher brain centers to suppress the FSH surge and the ensuing compensato

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00101.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Shida CS, Castrucci AML, Lamy‐Freund MT. High melatonin solubility in aqueous medium. J Pineal Res. 1994:16:198–201.AbstractThe pineal hormone melatonin (5‐methoxy‐N‐acetyl‐tryptamine) has been reported to participate in important physiological processes. Although some of its biological actions seem to depend on a protein receptor at the membrane surface, melatonin is known to interact with a large variety of tissues and cells, suggesting that the molecule may not necessarily interact through a specific membrane receptor at a specific cell. Most discussions of melatonin activity have assumed that the molecule is highly hydrophobic. Contrary to belief, the present work shows that melatonin is soluble in a purely aqueous medium up to 5 ± 10‐3M and describes a new method of melatonin preparation which shows the high hydrophilicity of the molecule. The results presented will affect the current biological hypothesis on the need of a melatonin carrier in the blood stream or the mechanisms which allow the hormone to cross the cell membrane and interact at the level

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00102.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Mockett BG, Lapwood KR. Changes in ovine pineal gland neuron‐specific enolase immunoreactivity following bilateral, but not unilateral, superior cervical ganglionectomy's. J. Pineal Res. 1994:16:202–209.AbstractPineal gland tissue from control and from unilaterally or bilaterally superior cervical ganglionectomized (SCGX) sheep was found to contain neuron‐specific enolase immunoreactive cells and nerve fibers. Morphological characteristics of pineal cells exhibiting immunoreactivity indicated that they were predominantly pinealocytes, while other cell types were nonimmunoreactive. Whereas bilateral SCGX resulted in a reduction in the size, and possibly number, of immunoreactive cells in the pineal, unilateral denervation did not result in any significant effects when compared with control pineals. Concomitant with the reduction in immunoreactivity in bilaterally denervated pineals was a significant increase in the volume of interstitial space, but not the number of nonimmunoreactive cells. These results suggest that sympathetic nerve fibers innervating the pineal of unilaterally sympathectomized sheep exhibited a degree of neural plasticity that resulted in denervated pinealocytes being reinnervated by remaining intact nerve terminals, thus preventing the occurrence of degenerative changes normally associated with complete loss of neural input through bilateral denervation. The fact that in unilaterally denervated sheep neither left nor right SCGX produced any discernible effects in either half of the pineal indicates that nerve fibers from each of the ganglia cross over to innervate the contra lateral as well as the ipsilateral pineal half. In the stalk of the pineal an extensive network of immunoreactive nerve fibers was found in both the caudal and habenular commissars, and occasionally these fibers were observed to enter the body of both intact and sympathetically denervated pineals. This latter result suggests that the sympathetic innervation enters the pineal over its surface and not via the

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00103.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Guerrero JM, Reiter RJ, Poeggeler B, Chen L‐D, Tan D‐X. Elevation of cyclic GMP levels in the rat pineal gland induced by nitric oxide. J Pineal Res. 1994:16:210–214.AbstractThe present paper reports that nitric oxide (NO) released by sodium nitroprusside (SNP) is a potent activator of rat pineal cyclic GMP production without affecting cyclic AMP synthesis. Other drugs such as isoproterenol, vasoactive intestinal peptide, and peptide histidine isoleucine were ineffective in stimulating cyclic GMP production, but activated cyclic AMP production. However, L‐arginine, the physiological precursor of NO, did not activate either cyclic GMP or NO synthesis. Because L‐arginine failed to activate cyclic GMP production, results suggest that NO is not produced in the pineal gland, but behaves as a potent regulator of this cyclic n

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00104.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY

摘要:

Crespo D, Fernández‐Viadero R, Verduga R, Ovejero V, Cos S. Interaction'between melatonin and estradiol on morphological and morphometric features of MCF‐7 human breast cancer cells. J. Pineal Res. 1994:16:215–222.AbstractMelatonin has been shown to have a direct inhibitory effect on the proliferation of estrogen‐responsive MCF‐7 human breast cancer cells, involving an interaction with estradiol. The anti‐proliferative effect of melatonin is reversed by the addition of estradiol to the culture. In the present study, we examined whether inhibition by megaton and subsequent estrogen rescue of MCF‐7 cells are correlated with morphological and morph metric changes in these cells. After 4 days of exposure to melatonin, MCF‐7 cells showed significantly smaller cell and nuclear sizes than other groups. These morphometric results were closely related to the ultra structural features observed in these cells. While control and estradiol‐treated cells showed increased tumor characteristics, melatonin‐treated cells presented greater differentiation, in keeping with their epithelial origin (presence of cytokeratin filament bundles, conspicuous rough endoplasmic reticulum, and Golgi cisternae together with the presence of prominent nucleoli at the nuclear level). Additionally, some melatonin‐treated cells displayed degenerative features (mitochondrial swelling with disruption of cristae, cytoplasmic vacuolation, nuclear chromatin disgregation and cell lysis). The addition of estradiol to cells previously incubated with melatonin reversed the changes induced by the latter and these cells showed the same ultrastructural features as the control cells. Our results support the notion that melatonin exerts its antitumor effect through a cell‐cycle‐specific mechanism by delaying the entry of MCF‐7 cells into mitosis. This allows the tumor cells to achieve greater differentiation. The fact that the morph metric and morphological effects induced by megaton are counteracted by estrogens suggests a cell‐cycle acc

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1994.tb00105.x

出版商:Blackwell Publishing Ltd    

年代:1994

数据来源: WILEY