Central alpha-MSH infusion in rats: Disparate anorexic vs. metabolic changes with aging

Changes of the anorexigenic and hypermetabolic components of the overall catabolic effect of alpha-MSH were studied in rats as a function of age. In male Wistar rats a 7 day-long intracerebroventricular infusion of alpha-MSH suppressed food intake and caused a fall in body weight in 2 and 3–4 month-old (young) groups, but it was most effective in the 24 month-old group and had hardly any effect in the 12 month-old (middle-aged) animals. In contrast, metabolic rate as well as biotelemetric measurements of core temperature and heart rate revealed the most pronounced hypermetabolic effects of such infusions at age 12 months. The hypermetabolic effect was still high in the oldest group, but low in the younger groups. In conclusion: Changes of the anorexigenic and hypermetabolic effects in the course of aging are not concordant. The overall catabolic activity of alpha-MSH is smallest in the middle-aged and highest in the oldest group. ►Catabolic action of alpha-MSH is smallest in middle-aged, extreme in old rats. ►In young rats alpha-MSH acts mainly by suppressing food intake. ►In middle-aged rats the alpha-MSH-induced hypermetabolism dominates. ►In aged rats both anorexia and hypermetabolism are pronounced. ►Anorexigenic and hypermetabolic effects of MSH during aging change disparately.