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 BW (FI/BW). Selection occurred for both criteria in each of 3 replications (R); an unselected control (MC) was also maintained in each replicate. A total of 25 generations of selection was practiced; the 9 lines are presently maintained without selection. 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 218 male mice measured in the present study came from R1-R3 and multiple generations. The purpose of this study was to determine hepatic mitochondrial efficiency in mice at maintenance across the genetic lines. Additionally, line comparisons of BW, FI/BW, liver weight per BW (LW/BW), and body composition were analyzed. Following measurement of FI and BW over a 2-wk period, mice were euthanized, and their livers were extracted and weighed. 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 \u3c 0.03) respiratory control ratio by 22% than that for MH mice, revealing greater degree of uncoupling, thus less efficient electron transport in MH mice. There were no line differences (P \u3e 0.99) in ADP:Oxygen ratio. There was no difference in BW between MH and ML mice (P \u3e 0.35), however MC mice were heavier (P \u3c 0.02). Difference in FI/BW (P \u3c 0.001) was large with MH mice consuming 34% more than ML mice. No line differences in LW/BW were found. Selection tended to affect on fat percentage (P \u3c 0.07) with ML mice being 19% fatter than MH mice. RCR 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. Adviser: Merlyn K. Nielse