摘要:

Abstract:The effects of melatonin (25 μg s.c. daily in the late afternoon for 10 days) on the ovarian morphometry and the gonadotropin secretion were investigated in food‐restricted rats and rats fed ad libitum. In food‐restricted rats melatonin produced the significant decrease of the surface area of the ovary and of zona granulosa. Moreover, melatonin treatment of food‐restricted rats resulted in significant diminishment of the relative areas of Graafian follicles and zona granulosa estimated in relation to the ovary cross‐sectional surface area. On the other hand, melatonin did not produce significant alterations of the morphometric indices of the ovary in rats fed ad libitum. Melatonin administration was found to inhibit the effects of gonadoliberin on gonadotropin release in food‐restricted but not in normally‐fed rats. These findings suggest that food restriction sensitizes the pituitary‐ovarian axis to antigonadotropic me

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00047.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The recent development of a specific 2‐[125I]‐iodomelatonin ligand has led to the identification of I‐melatonin binding sites in the brains of numerous mammalian species. The present study reports the localization of125I‐melatonin binding sites in the brain of the dairy goat. Six previously untreated female goats, aged 5–7 years, were culled under natural light between 0900 and 1100. Brains and pituitaries were immediately dissected out and frozen on dry ice. Both transverse and sagittal sections of frozen brain were cut 20 μm thick and thaw‐mounted onto gelatine‐coated slides. Three consecutive sections were cut at intervals throughout the brain, mounted onto three slides, labeled A, B, and C, and thusly treated: (A) incubated for 2 hr at room temperature in a 50 pM solution of125I‐melatonin; (B) incubated for 2 hr at room temperature in a 50 pM solution of125I‐melatonin plus 1 μM cold melatonin; (C) fixed in Clarke's fluid and stained with toluidine blue. After incubation, A (specific) and B (nonspecific) slides were washed three times in ice‐cold Tris‐HCl buffer (pH 7.7), air‐dried, exposed to an X‐ray film for 2 weeks at ‐20°C, and then fixed and stained. Specific125I‐melatonin binding sites were found in the pars tuberalis (PT), the area of the suprachiasmatic nucleus (SCN), preoptic area (POA), fornix/mediolateral septal areas, hippocampus, and the cerebral cortex.125I‐melatonin did not bind in the hindbrain, midbrain, neurohypophysis, pars intermedia or pars distalis of

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00048.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The objective of this study was to determine whether melatonin (aMT) influences the postnatal development of the mammary gland parenchyma in female mice from the time of weaning to adulthood. Twenty‐one‐day‐old female BALBc mice were treated with daily subcutaneous injections of aMT (200 (μg) or diluent, 3 hr before the onset of darkness (photoperiod LD 12:12). At 3, 5, 7, 9, 11, and 13 weeks of age, batches of 20 animals (ten controls and ten aMT‐treated) were sacrificed and the second pair of mammary glands were dissected to evaluate their degree of development. Melatonin decreased body weight gain from 2 weeks before until 2 weeks after the onset of puberty. Treatment with aMT also resulted in a lower DNA content and smaller area of the mammary gland from the time of puberty until the end of the study. In aMT‐treated mice the phase of highly positive allometric growth began 2 weeks later, but ended at the same time as in controls (11th week of life). Finally, aMT decreased the development of terminal, lateral, and alveolar buds while it increased the number of terminal ducts per gland. We conclude that pharmacological doses of aMT (1) reduce body weight gain at the peripuberal age; (2) partially inhibit postnatal mammary gland development by reducing the number of epithelial structures representing sites of growth and increasing that of structures representing the final state of ductal growth in virgin animals; (3) delay the onset of and shorten the phase of rapid mammary growth occurring in early postp

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00049.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:Male Syrian hamsters that were exposed for 8 weeks to short photoperiod (LD 10:14) or treated with melatonin in the late afternoon under long photoperiod conditions (LD 14:10) had a significantly higher content of androgen receptors in the Lipidex‐purified soluble fractions isolated from the Harderian glands as compared to the long photoperiod (LD 14:10) exposed controls. Simultaneous computer‐assisted analyses of all series of saturation and competition experiments revealed that the numerical value of the apparent Kd, as determined by using the synthetic androgen R‐1881 (methyltrienolone), was not different between the experimental groups, and ranged from 0.050 to 0.067 nM. Of the principal natural androgens, testosterone (T) was most potent in inhibiting methyltrienolone binding to the receptor (Ki values from 0.33 to 0.55 nM), and 5α‐dihydrotestosterone (DHT) and α4‐androstenedione (AD) were less effective (Ki values between 1 and 1.9 nM). In the hypothalami and pituitaries of the same animals, used in parallel control assays, DHT was twice as potent as T. Short‐term castration (24 hr post‐orchidectomy) did not result in significant changes in the receptor binding characteristics. Following 8 weeks exposure to a long photoperiod (LD 14:10) the Bmax values demonstrated a four‐fold increase in castrated animals (179 fmoles/mg protein vs. 47 fmoles/mg protein) over intact controls. The relative binding affinity of the major androgens under these conditions remained unchanged, with the exception of AD, where a five‐fold increase in the numerical Ki values (decrease in the binding affinity) was recorded (Ki = 9.6 nM). Studies on in vitro metabolism of the natural androgens by the cytosol during incubation under conditions identical to those employed in the binding studies revealed that in the normal intact animal AD is metabolized to T in elevated amounts. The ability of the Harderian gland to make this conversion is dramatically diminished following long‐term castration. This could explain the apparent “shift” in the high affinity of AD toward a much lower one. Testosterone, however, was not further metabolized. No DHT was formed and small amounts of AD were recovered. Thus, in the androgen receptor system of the hamster Harderian gland testosterone appears to be a strong androgen per se, binding to the receptor with affinity higher than that of DHT. This receptor system is apparently flexible in its response to changes in the photoperiod and to removal of the natural steroids from the endogenous milieu following long‐term castration. Both situations are accompanied by a significant increase in receptor numbers, though castration seemingly results in concomitant changes in the andro

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00050.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:Seasonal variations in daytime pineal 5‐methoxytryptophol (5‐ML) and in the daily pattern of both pineal 5‐ML and melatonin concentrations were measured by radioimmunoassay in male and female jerboas,Jaculus orientalis. Pineal 5‐ML content was found to be low in winter and spring and showed a short but marked increase in summer. A clear daily rhythm was present in pineal 5‐ML in September, with high concentrations during daytime and low concentrations during nighttime. In May there was a considerable drop in the daytime values and a marked decrease in the amplitude of the rhythm, while in December the daily rhythm completely disappeared. On the contrary, a clear daily rhythm was observed for pineal melatonin in September, December, and May with high values during nighttime and low values during daytime; no differences in the amplitude of the rhythm could be observed. Illumination during early night prevented both the nocturnal decrease of 5‐ML and the increase of melatonin in September; in May illumination had no clear effect on 5‐ML, while it prevented the normal increase of melatonin. These results suggest a possible desynchronization between the regulation of 5‐ML and melatonin synthesis and release, and stress the complexity of the mechanisms involved in the environmental synchronization of sea

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00051.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:The duration of nighttime synthesis of the pineal hormone melatonin is believed to determine the breeding season in many mammalian species. Hamsters exposed to short days undergo gonadal involution followed by a return to normal function, suggesting a developed insensitivity to regressive photoperiods. This recrudescence may be due to either exhaustion of the pineal or to target‐desensitization. Both theories have been tested previously but failed to explain this phenomenon. We performed an experiment in the Djungarian hamster (Phodopus sungorus), a well‐characterized photosensitive species with a type C melatonin pattern (prolonged peak during majority of dark phase), in an attempt to resolve this issue. Among age‐matched male hamsters exposed to short days for either 16 weeks (involuted) or 38 weeks (spontaneous recrudescent), marked phase differences in diurnal pineal melatonin rhythms were observed. Furthermore, in recrudescent hamsters the melatonin pattern was divided into two parts, possibly no longer recognizable as a typical short‐day

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00052.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Abstract:Cultured chick pineal glands show a persistent rhythm in the rate of cumulative incorporation of thymidine into DNA [Wainwright and Wainwright, 1989]. In this study we have examined the effects of a pulse‐exposure to ouabain in the dark on the first day of culture upon thymidine incorporation during the second and third days of culture in the dark with ouabain‐free medium. The phase of the rhythm in rate of thymidine incorporation was delayed by a 4‐hr exposure to 100 μM ouabain commencing in the final hour of the photoperiod, but not by a 2‐hr exposure or by 10 μM ouabain. This effect was phase‐dependent and not seen when exposure to ouabain began earlier in the photoperiod. The phase delay caused by ouabain was not due to a persistent direct inhibition of the process of thymidine incorporation. The phase‐shift due to exposure to ouabain was superimposed on a phase delay caused by renewal of culture medium 4 hr after explanting the glands

ISSN:0742-3098    

DOI:10.1111/j.1600-079X.1992.tb00053.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY