LEPTIN INCREASES ENERGY-EXPENDITURE OF A MARSUPIAL BY INHIBITION OF DAILY TORPOR

Leptin plays an important role in regulating body fat stores of placen tal mammals, but the contribution of changes in energy expenditure to this adjustment remains controversial. We were interested in how recom binant murine leptin would affect metabolic rate (MR) and body tempera ture (Tb) Of a marsupial mammal (Sminthopsis macroura, 25 g) known to display daily torpor but lacking thermogenetically active brown adipos e tissue. In a group of eight animals deprived of food for 1 day at 18 degrees C, leptin treatment halved the duration of torpor bouts (time at T-b < 30 degrees C) and raised the average daily minimum Tb by 4.5 degrees C and minimum MR by 2.2-fold. Leptin treatment thus increased daily energy expenditure by 9%, although MR and Tb during the activit y phase were not raised. Body mass was also not affected. These findin gs in a marsupial suggest that the adjustment of thermoregulatory ener gy expenditure during the rest phase in accordance with energy availab ility is a phylogenetically old function of leptin.