Modulation of leptin sensitivity by short photoperiod acclimation in the Djungarian hamster, Phodopus sungorus |
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Authors: | M Klingenspor H Niggemann G Heldmaier |
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Institution: | (1) Animal Physiology, Department of Biology, Philipps University, 35032 Marburg, Germany e-mail: Martin.Klingenspor@mailer.uni-marburg.de Tel.: +49-6421-2823908; Fax: +49-6421-2828937, DE |
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Abstract: | During seasonal acclimation, Djungarian hamsters spontaneously exhibit a reduction in food intake, body mass and body fat
stores, which is externally cued by shortening of day length in autumn and controlled by a sliding set-point. We investigated
the function of the leptin adipostatic feedback system in the photoperiodic control of seasonal acclimation. In response to
mouse recombinant leptin injections for 10 days, long day photoperiod (LD) and short day photoperiod (SD)-acclimated hamsters
decreased food intake and body mass. The reduction of body mass was due to the depletion of body fat, as revealed by carcass
composition analysis. In SD hamsters, leptin caused a larger reduction of body fat mass than observed under LD conditions,
whereas the anorectic effect was similar in both photoperiods. The serum leptin concentration was 9.3 ± 1.2 ng/ml in LD-acclimated
hamsters and decreased significantly to 4.2 ± 0.8 ng/ml and 2.1 ± 0.6 ng/ml in hamsters exposed to SD for 66 days and 116
days, respectively (P < 0.001). A strong positive correlation between total body fat mass and serum leptin concentration was found (r
S=0.935, P < 0.0001, n=70). Despite the anorectic action of exogenous leptin, higher endogenous leptin levels in LD hamsters were paralleled by
higher food intake in LD hamsters as compared to SD hamsters. This paradoxical finding further supports the increased leptin
sensitivity in SD hamsters as judged from leptin treatment experiments. We tested the functional significance of leptin for
the controlled down-regulation of food intake and body mass induced by short photoperiod. Food restriction for 10 days during
the transition phase decreased body mass below the desired sliding set-point, which was recovered in control hamsters following
ad libitum refeeding. Treatment with mouse recombinant leptin during ad libitum refeeding inhibited the recovery of body mass
and blunted the increase of food intake observed in controls, indicating that the sliding set-point utilizes leptin as a signal
for the adjustment of the appropriate body mass level.
Accepted: 15 October 1999 |
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Keywords: | Body weight Melatonin Sliding set-point Adipose tissue Energy expenditure |
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