The aim of the study was to investigate how leptin and ghrelin contribute to winter-acclimatization in the Siberian hamster (Phodopus sungorus).

Adult female (n = 17) and male (n = 14) Siberian hamsters were divided into control, winter-acclimatization (WA), melatonin (MEL) or short-day (SD) groups. Control and MEL groups were maintained in 12L:12D and at Ta 22 ± 2°C, while WA and SD groups had 8L:16D and Ta of 10 ± 2°C or 22 ± 2°C, respectively. Body temperatures were recorded, using i.p. data loggers. Melatonin was given trough subcutaneous capsules (release rate: 12 mg/24-hours).

Plasma leptin and insulin concentrations were significantly reduced in WA (p < 0.01; p < 0.001), MEL (p < 0.05; p < 0.05) and SD (p < 0.01; p < 0.01) groups. Plasma ghrelin concentration was increased in WA group (p < 0.01) and melatonin in MEL group (p < 0.001). Night- and day-time body temperatures in WA, MEL and SD hamsters were lowered (p < 0.001 in all cases) throughout the study and torpor bouts were observed (Ta<32°C). Percentual fat content of the carcasses were significantly lower in all treated groups.

Siberian hamsters reduce their feeding in winter, though reduced leptin concentration in all treated groups and increased ghrelin concentration in WA group suggest just the contrary. The permissive role of leptin on reproduction was absent in treated groups, which reduced gonadal testosterone concentration. It appears that torpor bouts in Phodopus are related to lowered leptin and body weight. Mere increase of circulating melatonin does not affect on ghrelin concentration but requires cold-treatment also. Increased ghrelin may modify the feeding behaviour by activating food hoarding in WA group.