Influence of Morning Melatonin Injections on the Antigonadotrophic Effects of Afternoon Melatonin Administration in Male and Female Hamsters

Richardson, Bruce A.; Vaughan, Mary K.; Brainard, George C.; Huerter, Joachim J.; Santos, R. de los; Reiter, Russe J

doi:10.1159/000123213

Cited by 19 publications

(7 citation statements)

References 23 publications

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“…The data are, in principal, well in accor dance to previously described experiments [1, 4-6, 8, 9, 12, 14, 15, 17, 19, 22-25, 27, 28]. It is generally believed that the duration of melatonin synthesis is the main factor responsible for the physiological effects of short-day photoperiods [3,4,7,15,[22][23][24]. However, other the ories exist which take into account that similar melatonin patterns in hamsters, exposed to a similar photoperiod, may induce opposite effects depending on the lighting conditions the animals were initially exposed to.…”

Section: Discussionsupporting

confidence: 84%

“…by daily collection of vaginal smears). In the Syrian hamster, there is evidence indicating sexual dimorphism in response to melatonin on reproductive organs [2,24], In the present study the effects of changes in photoperi ods were investigated in female Djungarian hamsters. In particular, comparisons of the diurnal profiles of melato nin synthesis as well as the profiles of its main precursor, serotonin, and 5-hydroxyindole acetic acid (5-HIAA), a metabolite of serotonin, were studied.…”

Section: -| a C Y C Licmentioning

confidence: 96%

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Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus

Lerchl¹,

Schlatt²

1993

Neuroendocrinology

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In order to investigate female Djungarian hamsters’ reactions to changes of the photoperiod, the following two experiments were performed. Experiment I: Age-matched female hamsters were exposed to either short (8L:16D) or long days (16L:8D) for 38 weeks. Initially, the short-day group showed a decline in body weight, associated with changes in gonadal function and fur color. This was not maintained by the short-day group which returned, on the most part, to long-day levels, thus becoming insensitive to this regressive lighting regimen. The time courses of these events compare well with those observed in males, which suggests a common mechanism. Experiment II: Two groups of female hamsters were exposed for 8 weeks to either long days or short days. At the end of the test period, the diurnal variations in pineal content of melatonin, serotonin, hydroxyindole acetic acid, and serum melatonin were estimated, revealing marked differences between the two groups. Not only was there a prolongation of melatonin synthesis observed in the short-day animals, but there was also a significant elevation of the melatonin levels when compared to the long-day animals. Together with recent findings in males, these findings lend support to the hypothesis that, in the Djungarian hamster, the elevation of nocturnal melatonin levels may be of additional significance, with respect to the physiological changes induced by short-day photoperiods.

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Section: Discussionsupporting

confidence: 84%

Section: -| a C Y C Licmentioning

confidence: 96%

Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus

Lerchl¹,

Schlatt²

1993

Neuroendocrinology

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“…It is also possible that the contradictory findings in the current study may be due to modulation of the pituitary hormone prolactin caused by experimental conditions as observed by other investigators [29] which might have a different effect on immature and mature prostate glands.…”

Section: Discussioncontrasting

confidence: 58%

Role of the pineal gland in the regulation of prostatic androgen receptors in pubertal and mature rats

Moêller

Rödl

et al. 1983

Res. Exp. Med.

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The effects of exposure to continuous light, continuous darkness, and administration of melatonin on prostatic androgen receptors in relation to pubertal development in rats were examined. Darkness produced dissimilar results between the pubertal and adult groups. Whereas the prostate weight in the pubertal group remained unaltered, it increased in the adult group. In the pubertal group exposed to darkness, plasma melatonin increased significantly, and androgen receptors declined, whereas in the adult group these receptors rose significantly with a simultaneous increment of melatonin concentration in plasma. Exposure to continuous light did not produce any effective alterations in the parameters examined. The afternoon melatonin administration showed trends similar to those seen in animals exposed to darkness. The results indicate that exposure to darkness or administration of melatonin both have age-dependent effects on prostatic androgen receptors. Exposure to darkness may interfere with the process of sexual maturation in the pubertal animal as a result of increased melatonin production.

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“…In such a case no storage takes place and a concentration peak is absent. This may explain the findings of Tamarkin et al (1976Tamarkin et al ( , 1977, Reiter et al (1976), and Richardson et al (1981) who found gonadal atrophy in hamsters kept under long photoperiods (LD 14 : 10) when the animals were injected with aMT just before the beginning of the dark period. At this time never a high concentration of aMT in the pineal was found.…”

Section: Discussionmentioning

confidence: 82%

Rhythmic synthesis of various 5-methoxyindoles in the pineal gland of male adult golden hamsters, kept under the same artificial conditions throughout the year

Benthem

Mans

Ebels

et al. 1985

J. Neural Transmission

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Until now the day/night and seasonal rhythmicity in the synthesis of 5-methoxyindoles (MI) is thought to be regulated by environmental factors, especially photoperiod and temperature. Endogenous factors are also implicated in the generation of N-acetyltransferase and hydroxyindole-O-methyltransferase activity rhythms. In the present experiments seasonal rhythmicity in the synthesis of MI in the pineal gland was investigated in hamsters kept under the same artificial conditions throughout the year. Though the environmental conditions were the same, day/night and seasonal rhythmicity in the production of MI in the pineal were observed indicating the existence of endogenous factors influencing the rhythmicities. In November, most of the MI showed the highest synthesis, MA and ML excepted, which were especially produced in July and September. The results obtained sustain the hypothesis that aMT is synthesized from MT rather than from aHT. Moreover, the rhythmicities in aMT synthesis are not identical to those found in aMT concentration as described in the literature. This indicates that synthesis and concentration of a compound are not comparable. At the end of the light period, when aMT injections have an antigonadotropic effect, a peak of aMT synthesis was always present. Although MI synthesis showed seasonal rhythmicity, no reproductive cycle occurred in the hamsters. At present, the concept that the pro- and/or antigonadal effects of the pineal are mediated by aMT seems to be the most acceptable. The present results, however, indicate that aMT and perhaps other MI, often regarded as factors influencing gonadal growth in golden hamsters, are not the only factors involved.

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Influence of Morning Melatonin Injections on the Antigonadotrophic Effects of Afternoon Melatonin Administration in Male and Female Hamsters

Cited by 19 publications

References 23 publications

Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus

Influence of Photoperiod on Pineal Melatonin Synthesis, Fur Color, Body Weight, and Reproductive Function in the Female Djungarian Hamster, Phodopus sungorus

Role of the pineal gland in the regulation of prostatic androgen receptors in pubertal and mature rats

Rhythmic synthesis of various 5-methoxyindoles in the pineal gland of male adult golden hamsters, kept under the same artificial conditions throughout the year

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