Metabolic differences between white and brown fat from fasting rabbits at physiological temperature

Abstract

It has been suggested that activated brown adipose tissue (BAT) shows increased glucose metabolic activity. However, less is known about metabolic activity of BAT under conditions offastingandnormal temperature.The aimof this studywas tocomparethepossible differences in energetic metabolism between BAT and white adipose tissue (WAT) obtained from rabbits under the conditions of physiological temperature and 24 h after fasting conditions. The studywas carriedoutonNewZealandrabbits (nZ10)maintainedfor aperiodof 8 weeks at 23G2 8C. Food was removed 24 h before BAT andWATwere obtained. Protein expression levels of the glycolytic-related protein, glyceraldehyde-3-phosphate dehydrogenase, and pyruvate dehydrogenasewerehigher inWAT than that inBAT. The expressionlevel of carnitine palmitoyltransferase 1 (CPT1) and CPT2, two fatty acidmitochondrial transporters, andthe fatty acidb-oxidation-relatedenzyme, acylCoAdehydrogenase,washigher inBAT than inWAT. Cytosolic malate dehydrogenase expression and malate dehydrogenase activity were higher inWAT than in BAT. However, lactate dehydrogenase expression and lactate content were significantly higher in BAT than inWAT. In summary, this study for the first time, to our knowledge, has described how under fasting and normal temperature conditions rabbit BAT seems to use anaerobic metabolism to provide energetic fuel, as opposed toWAT, where the malate-aspartate shuttle and, therefore, the gluconeogenic pathway seem to be potentiated.