Pineal Melatonin Content in Male Hamsters throughout the Seasonal Reproductive Cycle

Rollag, Mark D.; Panke, Elizabeth S.; Reíter, Russel J.

doi:10.3181/00379727-165-40981

Cited by 56 publications

(22 citation statements)

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“…Further, they are consistent with findings that the patterns of melatonin secretion in ewes maintained in natural photoperiodic conditions remain ap propriate to day length throughout the annual reproductive cycle, including during the reproductive transitions when animals may be refractory to the prevailing day length [2,13,27,29,30]. It is of interest that a normal 24-hour rhythm of pineal melatonin content has also been observed in pho torefractory golden hamsters [31].…”

Section: Pho To S E N S It IV E D Ev E Lo Pin G ___p H O T O R E F R supporting

confidence: 72%

Reproductive Refractoriness of the Ewe to Inhibitory Photoperiod Is Not Caused by Alteration of the Circadian Secretion of Melatonin

Malpaux¹,

Moenter²,

Wayne³

et al. 1988

Neuroendocrinology

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The 24-hour pattern of melatonin secretion was determined in 5 Suffolk ewes during extended exposure to a long day length to assess whether the eventual loss of response (photorefractoriness) to inhibitory long days resulted from an alteration in the circadian secretion of melatonin. Determinations of the secretory profile of melatonin were made once in short days (8 h light/day) before the switch to long days, and 11 times throughout the 250-day period of exposure to long days (16 h light/day). Samples were obtained hourly for 24 or 48 h. Reproductive state was assessed by response to estradiol-negative feedback, monitored as serum LH in ovariectomized ewes bearing estradiol implants. The characteristic secretory pattern of melatonin (low during the day, high at night), the duration of the melatonin elevation, and its phase relative to the light/dark cycle did not change as ewes became refractory to the inhibitory effects of long days. These results are consonant with the hypothesis that refractoriness of the ewe to inhibitory day length does not result from an alteration of the circadian rhythm of melatonin secretion.

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Section: Pho To S E N S It IV E D Ev E Lo Pin G ___p H O T O R E F R supporting

confidence: 72%

Reproductive Refractoriness of the Ewe to Inhibitory Photoperiod Is Not Caused by Alteration of the Circadian Secretion of Melatonin

Malpaux¹,

Moenter²,

Wayne³

et al. 1988

Neuroendocrinology

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“…Contrary to what has been claimed for some time Rollag et al, 1980 ;Tamarkin et al, 1980) this also appears to be true in the Syrian hamster (Roberts et al, 1985 ;Skene et al, 1987). Similar data were also obtained in the sheep (review in Arendt, 1986) Recently this hypothesis has been further elaborated and two models, the internal coincidence and the external coincidence ones, being proposed (Reiter, 1987b).…”

mentioning

confidence: 56%

The role of the pineal gland in the photoperiodic control of reproduction in different hamster species

Pévet¹

1988

Reprod. Nutr. Dévelop.

130

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“…In addition, Nett and Niswender (1982) observed that daily afternoon injections of melatonin could prolong the breeding season of the ewe, but the duration of this effect was limited t o a few weeks. Along similar lines, studies in the golden hamster, a long-day breeding species, have suggested that refractoriness t o short days is caused by a loss of responsiveness t o melatonin (Bittman, 1978;Reiter et al, 1979) and that the 24-h pattern of melatonin contained in the pineal gland does not change in relation to photorefractoriness (Rollag et al, 1980). Although our observations are consistent with these earlier findings, they conflict with those of Almeida and Lincoln (1984) who described abnormal melatonin profiles in Soay rams already refractory t o either short or long day lengths.…”

Section: Discussionmentioning

confidence: 95%

“…In the study of Almeida and Lincoln (1984), altered melatonin patterns were not observed until after refractoriness was expressed in terms of testicular size. Further, in previous studies of pineal melatonin content in rodents (Rollag et al, 1980), it was not possible to monitor the time course of melatonin secretion in the same animals as photorefractoriness progressed because a single measurement of the hormone required the removal of its source. Our present observations were made before the switch from long t o short days and then continued repeatedly until shortday refractoriness was fully expressed 100-1 50 days later.…”

Section: Discussionmentioning

confidence: 97%

Reproductive refractoriness of the ewe to inductive photoperiod is not caused by inappropriate secretion of melatonin

Malpaux

Robinson

Brown

et al. 1987

Biology of Reproduction

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The 24-h pattern of melatonin secretion was evaluated in Suffolk ewes during prolonged exposure to an inductive photoperiod to assess whether altered secretion of melatonin could account for the eventual loss of response to stimulatory photoperiod (photorefractoriness). Secretory patterns of melatonin were determined approximately every two weeks in samples obtained hourly for 24-48 h. Sampling was begun one week before the switch from inhibitory (long) to inductive (short) photoperiod and continued for 150 days, by which time all but one of the ewes were unresponsive to that stimulatory day length. Melatonin was measured in two different radioimmunoassay systems. Reproductive state was monitored by luteinizing hormone secretion in ovariectomized ewes bearing constant-release estradiol implants. No evidence for disruption of the melatonin pattern was observed on any occasion. The duration and the phase of the melatonin elevation relative to the light/dark cycle did not vary with time of exposure to short days. These findings indicate that refractoriness of the Suffolk ewe to an inductive photoperiod is not caused by an inappropriate secretory pattern of melatonin.

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Pineal Melatonin Content in Male Hamsters throughout the Seasonal Reproductive Cycle

Cited by 56 publications

References 0 publications

Reproductive Refractoriness of the Ewe to Inhibitory Photoperiod Is Not Caused by Alteration of the Circadian Secretion of Melatonin

Reproductive Refractoriness of the Ewe to Inhibitory Photoperiod Is Not Caused by Alteration of the Circadian Secretion of Melatonin

The role of the pineal gland in the photoperiodic control of reproduction in different hamster species

Reproductive refractoriness of the ewe to inductive photoperiod is not caused by inappropriate secretion of melatonin

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