Plasma melatonin concentration in hibernating marmots : absence of a plasma melatonin rhythm [Concentration de la mélatonine plasmatique chez les marmottes hibernantes : absence d'un rythme de mélatonine plasmatique].

Résumé

Plasma melatonin concentrations were measured thoughout bouts of hibernation in marmots maintained in a short photoperiod (light-dark 8:16) and ambient temperature of 5 or 15°C. Melatonin concentration was also measured in two animals maintained in constant darkness. As an animal entered hibernation, plasma melatonin concentration dropped to basal levels when body temperature reached 25°C, and they remained low until arousal. During deep hibernation plasma melatonin value did not vary significantly (P<0.05) with respect to time of day or different ambient temperatures. With nocturnal arousal plasma melatonin levels were similar to euthermic night values. Lack of a plasma melatonin rhythm during hibernation suggests that the pineal gland is not temperature compensated during hibernation, and due to the low tissue temperature of the pineal the circadian pacemaker driving melatonin secretion is incapable of stimulating a rhythm.