LEPTIN SELECTIVELY INCREASES ENERGY-EXPENDITURE OF FOOD-RESTRICTED LEAN MICE

OBJECTIVE: To find out whether leptin can attenuate hypometabolic torp or-like states of metabolic rate (MR) in adult lean animals, as it att enuates the morning suppression of thermoregulatory thermogenesis in s uckling-age rat pups. DESIGN: Leptin effects on MR and food intake wer e studied in mice aged 4-7 months, in which a high incidence of exagge rated circadian reductions of MR had been induced by chronic food-rest riction and, for comparison, in free-feeding mice. PROTOCOL: Continuou s recordings of MR, for a group of seven mice maintained at an ambient temperature of 24 degrees C, while they were repeatedly-with pauses o f at least six days-treated for three consecutive days with either rec ombinant murine leptin (20, 200 or 600 pmol.g(-1).d(-1)) or saline. RE SULTS: Leptin treatment caused dose-dependent 5-15% increases in energ y expenditure by moderating the decreases in MR during the circadian m inima, without affecting either the MR during the circadian maxima or food intake. Similar treatment of free-feeding mice caused dose-depend ent decreases of food intake without changing MR. CONCLUSION: Leptin c ontrols thermoregulatory energy expenditure when food supplies are sca rce and changes food intake, rather than energy expenditure, when food is abundant.