CHANGES INDUCED BY FASTING AND DIETETIC OBESITY IN THERMOGENIC PARAMETERS OF RAT BROWN ADIPOSE-TISSUE MITOCHONDRIAL SUBPOPULATIONS

The effects of starvation on the thermogenic parameters of three diffe rent mitochondrial subpopulations in brown adipose tissue (BAT) of bot h post-cafeteria obese and lean rats were investigated. Tissue from di fferent BAT depots from fed and 24 h starved rats were collected, pool ed and three mitochondrial subpopulations were isolated by differentia l centrifugation; the M1 fraction (1000 g), the M3 fraction (3000 g) a nd the M15 fraction (15000 g). Thermogenic parameters were measured in the three mitochondrial subtypes, and uncoupling protein (UCP) mRNA w as determined in BAT. The results showed that starvation induced a dec rease in mitochondrial turnover in BAT from both lean and obese rats. Moreover, a selective net loss of UCP from the lightest mitochondrial fraction (M 15) in lean rats, with a concomitant reduction of UCP mRNA was observed. The reductions did not occur in obese rats and, as a re sult, a change in UCP distribution between the mitochondrial subpopula tions was produced, with an increase in the M1 mitochondrial subtype. The lack of response of UCP to starvation observed in BAT of obese rat s compared with the decrease seen in lean animals, is a consequence of a different mitochondrial subpopulation composition and/or a differen t response of a particular subpopulation to starvation.