Hepatic mitochondrial efficiency in lines of mice differing in feed intake

Selection was practiced for high (MH) and low (ML) heat loss using direct calorimetry to create lines of mice differing in feed intake per unit average BW (FI/BW). A total of 25 generations of selection was practiced during maintenance of an unselected control (MC). As a percentage of MC, mice of MH and ML lines differed in heat loss and FI/BW by 56 and 34%, respectively, when selection ceased. The purpose of this study was to determine hepatic mitochondrial efficiency in mice at maintenance across the genetic lines. After measurement of feed intakeand BW over a 2-wk period, mice were euthanized, and their livers were extracted. Livers were homogenized and mitochondria were isolated in buffer for measurement of oxygen consumption and, hence, mitochondrial activity using a Clark-type oxygen electrode. Mitochondria of ML mice expressed greater (P < 0.03) respiratory control ratio by 22% than that for MH mice, revealing greater degree of uncoupling during electron transport in MH mice. Difference in FI/BW (P < 0.001) was large with MH mice consuming 34% more than ML mice. The respiratory control ratio differed between mice of MH and ML lines as expected; however, regression analysis revealed that it explained essentially no variation in feed intake per BW.