Aims: 

The maintenance of energy homeostasis involves both the regulation of body weight (BW) and that of core temperature (Tc). Alpha-melanocyte-stimulating-hormone (alpha-MSH) is a neuropeptide with coordinated catabolic actions: it decreases food intake (FI) and increases metabolic rate (MR). Our previous animal studies showed that the hyperthermic effect of alpha-MSH is not coordinated and it also depends on the ambient temperature and on initial Tc-s. Anorexigenic effects of centrally applied alpha-MSH showed characteristic age-related shifts with strong effects in young, diminished efficacy in middle-aged and very pronounced responsiveness in old rats. The aim of the present study was to discover, whether the thermoregulatory effects of alpha-MSH also show age-related alterations.

Methods: 

Thermoregulatory effects of an acute intracerebroventricular (ICV) alpha-MSH injection (0 or 5 mg) were analyzed in various age-groups (2-months: juvenile, 3-months: young adult, 12-months: middle-aged and 24-months: old) of male Wistar rats at a slightly subthermoneutral environment (25–26 °C). Core (Tc) and tail skin temperatures (Ts, indicating heat loss) of partially restrained rats were recorded by thermocouples linked to a 12-channel Digi-Sense Benchtop Thermometer (Cole Parmer). For measurement of oxygen consumption (VO2), cylindrical restraining cages of the animals were placed in metabolic chambers of an indirect calorimeter system (Oxymax Equal-Flow, Columbus).

Results: 

Alpha-MSH-induced hyperthermia was most pronounced in the young adult age-group. In these rats the hyperthermic effect of a significant increase in the VO2 was somewhat diminished by an simultaneous activation of vasodilatory mechanism indicated by a rise in Ts. Juvenile animals showed weaker hyperthermic responses, middle-aged rats none at all. However, alpha-MSH-induced hyperthermia became significant again in old rats.

Conclusions: 

Thermoregulatory responsiveness to an acute ICV alpha-MSH injection show similar age-related pattern to that observed in connection with anorexigenic melanocortin effects. Support: OTKA PD84241, PTE AOK-KA-34039-02/2010