摘要:

Abstract:Many studies of melatonin in human puberty are difficult to interpret in light of methodological considerations such as the use of single blood samples collected either during the day or at night; a small number of observations; the failure to include the temporal characteristics of melatonin secretion; the definition of puberty by the use of broad clinical features without use of hormonal markers of puberty; the lack of control for the actual duration and intensity of light exposure during the days preceding the study; and the cross sectional nature of most studies. The few studies that have examined the plasma melatonin rhythm in humans by multiple blood sampling overnight or over 24 hr suggest that normal pubertal development (as well as normal ovarian function) are not linked to alterations in the plasma melatonin profile. There is, however, some evidence to suggest that disorders of the hypothalamic‐pituitary‐gonadal axis (delayed puberty, precocious puberty, hypothalamic amenorrhea) may be linked to altered plasma melatonin profile, at least in some cases. These findings, taken together with strong evidence for the role of the pineal gland in the reproductive function of other vertebrate species, render unlikely the inference that the pineal gland has no role in the development and function of the human reproductive axis. Thus, one may speculate that a pineal‐puberty relation does exist in humans and that the research techniques applied to date have been inadequate to uncover this relation. Greater knowledge might be gained from studies of melatonin metabolism during growth and pubertal maturation, from longitudinal studies of the melatonin rhythm under rigorously controlled conditions of light exposure, and, perhaps, from the development of research strategies to explore the human melatonin receptor in

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00517.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Seasonal changes in the ultrastructure of the free‐living Rose‐Ringed ParakeetPsittacula krameripineal were examined in relation to the sub‐tropical environment and seasonal reproduction. Dark and light pinealocytes of the presumptive neuroendocrine cell line predominated, while supporting cells, ependymal cells, myelinated and non‐myelinated nerve fibers with nerve endings, and regressed photoreceptor elements were also observed. Unlike in pineals of many animals, particularly mammals, the presence of dense‐core vesicles (DCVs) with varying core density, and absence of clear vesicles and vacuoles with flocullent material, indicate the involvement of DCVs in the synthesis and secretion of pineals principle/s. In November (pre‐breeding) when the day length registered a drop to LD 10:14, pinealocytes showed significantly decreased and smaller DCVs and mitochondria, nuclei with heterochromatin, and greater distribution of glycogen and lipid droplets, all indicating low pineal metabolic activity. During the shortest day regime from December to March, when the birds peaked breading, the number and size of DCVs and mitochondria increased, and Golgi body‐endoplasmic reticulum‐lysosome complex (GERL) was very well defined. Images of DCVs suggested possible secretion of pineal principle/s by dissolution, and exocytosis. Coincidence of these features with peak gonadotrophic (circulating LH) and spermatogenic and testicular endocrine activity described previously suggested an active turnover of pineal products during this short day length regime when parakeets breed. In contrast, during the post‐breeding season (April onwards), when the day‐length increased to LD 13:11 and hypophyseal‐gonadal function was down, nuclei and RER continued to show active profile, the Golgi body and associated complex were moderately seen, and the DCVs and mitochondria were significantly smaller and lesser. It is therefore probable that the pineal is an important relay to translate cues related to less drastic sub‐tropical environmental change into DCV‐linked neurohormones that in turn may be involved in modulating seaso

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00518.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:The purpose of this study was to examine the day/night levels of pineal melatonin and its rate limiting enzyme N‐acetyltransferase (NAT) in relationship to the ratio of 11‐cis‐to all‐trans‐retinal. Three‐week‐old chicks were placed in 12:12 light: dark (LD 12:12) cycle for one week, pineals were collected during the light phase at 1500 (i.e., after 10 hr light), during the dark phase at 1900 (i.e., 2 hr after dark), at 2100 (i.e., 4 hr after dark), and at 2300 (i.e., 6 hr after dark) and after light extension to 1900. The results show that light‐sensitive 11‐cis‐retinal in the chick pineal has the same diurnal rhythm as NAT and melatonin; all constituents increased within 2 hr of darkness onset (at 1900) and reached their peak after 4 hr of dark. All values were lowest during the light phase at 1500. Low values for 11‐cis‐retinal, NAT, and melatonin were also seen in the group of chicks which experienced light extension to 1900. The data indicate that in vivo light plays a major role in triggering rhodopsin‐bound 11‐cis‐retinal production within 2–4 hr after darkness onset; this change likely serves as the signal for the subsequent formation of the hormonal product

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00519.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Melatonin is a hormone involved in neuroendocrine responses; its plasma concentrations display a circadian pattern which is modified by stress. Studies for determining the effects of stressors on melatonin levels in laboratory animals present the difficulty that the procedures for blood sampling are by themselves potential stressors capable of influencing the levels of the hormone measured. A simple non‐stressful method for measuring urinary excretion of melatonin has been consequently developed. The method is applicable to single undisturbed mice kept in conventional cages, and consists of urine collection on chromatographic paper followed by extraction and melatonin assay by radioimmunoassay. The use of this method with BD2F1 mice indicates nocturnal excretion of melatonin significantly higher than during the day; nighttime melatonin levels were shown to be suppressed by constant illumination. A significant increase in nocturnal melatonin excretion was caused by the application of rotational stress applied as a mild experimental stresso

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00520.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:Five adult pasture‐bred Prim Holstein cows were used to document the time invariance of melatonin disposition in the cow. Melatonin was administered by an intravenous route as a bolus (5 μg/kg of body weight) at either 1430 or 2230. Data were analysed according to a three‐compartment open model with melatonin elimination from the central compartment. The mean (±SD) kinetic parameters describing melatonin disposition, during day and night, respectively, were plasma clearances: 0.0267 ± 0.0084 1/kg per min and 0.0229 ±0.0031 1/kg per min; steady state volume of distribution: 0.826 ±0.229 1/kg and 0.780 ±0.193 1/kg; terminal half lives: 58.9 ±23.7 min and 64.1 ±33.7 min; mean residence times: 32.0 ±8.8 min and 33.9 ±6.2 min. No statistical difference was found between diurnal and nocturnal values for these parameters. These results support the concept of time invariance for melatonin kinetics in cattle and validate the use of diurnal experiments for the study of melat

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00521.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:The effects of microiontophoretic application of melatonin and melatonin plus vasotocin on spontaneously active neurons of caudate‐putamen in sham‐operated and pinealectomized rats were studied. Extracellular unit recordings showed that in sham‐pinealectomized rats, melatonin ejection primarily produced inhibition of the responsive neurons (74.1%), whereas only 24.9% of the neurons were excited. Iontophoretic ejection of vasotocin or melatonin + vasotocin produced, in both cases, an inhibition of 100% of the responsive neurons. In pinealectomized rats, iontophoretic melatonin ejection produced a similar percentage of inhibition (46.1%) and excitation (53.8%) of the responsive neurons. The simultaneous ejection of melatonin + vasotocin further increased the percentage of inhibition (88.8%) compared with the melatonin only treated group. Moreover, iontophoretic ejection of vasotocin inhibited 100% of the responsive neurons in pinealectomized rats. The actions of melatonin and vasotocin seem to be specific, because their effects are dependent on the amount of these compounds ejected, i.e., the intensity of the ejection current. These results indicate that the pineal compounds melatonin and vasotocin are neuromodulators of spontaneous neuronal activity of the rat caudate‐

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00522.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Abstract:The direct action of pineal melatonin on the renal system is supported by our demonstration of 2‐[125I]iodomelatonin binding sites in the male guinea pig kidney. Scatchard analyses and Hill coefficients revealed a single type of binding site with an equilibrium dissociation constant (Kd) of 22.3 ±1.6 pmol/1 and a maximum binding density (Bmax) of 0.99 ±0.03 fmol/mg protein (n = 7) at mid‐light. There was no significant difference in the Kd and Bmax values between kidney tissues collected at the middle of light and dark periods. The pharmacological profile of these 2‐[125I]iodomelatonin binding sites indicated high specificity for melatonin, 2‐iodomelatonin and 6‐chloromelatonin while kinetic studies generated a Kd value of 28.4 ±7.3 pmol/1 (n = 5) which was comparable to that determined from Scatchard transformations. Our results suggest that these binding sites are stable, reversible, saturable, specific, and of high affinity. Regional distribution study showed that specific binding of 2‐[125I]iodomelatonin was 8‐fold higher in the cortical region than that in the medullary region. Studies of subcellular distribution showed that 59.3% of binding sites were localized in crude nuclear fractions followed by crude mitochondrial fractions (22.3%) and crude microsomal fractions (18.3%) with no detectable binding in cytosolic fractions. Our present findings suggest the presence of putative melatonin receptors in the guinea pig kidney, which support the hypotheses of melatonin‐regulated renin secretion together with renal excretory functions via m

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1993.tb00523.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY