Meeting Abstract
36.3 Friday, Jan. 4 Energy metabolism of small muscle phenotype mice compared to inbred strains in response to exercise MIDDLETON, KM*; COATS, BR; University of Missouri; University of Chicago middletonk@missouri.edu
In recent years, studies of the skeletal system have revealed that it occupies a central role in whole-organism energy regulation via interactions with the autonomic nervous and endocrine systems. Much of this interaction is mediated by the adipocyte-derived hormone leptin, which has broad activity on appetite, energy expenditure, reproduction, and the skeletal system. Although the leptin-bone-insulin pathway has been extensively studied in leptin or leptin receptor knockout models, selection experiments may provide a novel system in which to address similar questions. We compared physiological parameters between an inbred line of high activity mice that exhibit a small muscle mutation and two inbred strains of mice that exhibit high and low bone mass phenotypes. The high activity mice were derived from a long-term selection experiment for high levels of voluntary wheel running. We divided mice from three strains into activity and stationary groups (n = 8 each) and recorded daily wheel activity for 10 weeks. Insulin and fasting glucose levels were assayed post wheel access, while circulating leptin was assayed both before and after wheel access. Insulin was significantly lower in the activity group but did not differ among strains. In contrast, fasting glucose did not differ between strains or treatments. Mini-muscle mice showed significantly higher initial leptin levels than the other strains, and were significantly lower in exercise groups. Leptin levels were more variable in sedentary mice across strains compared to the activity group. We conclude that mice with the small muscle phenotype exhibit a similar response to exercise as has been shown in other strains and that these mice might be an appropriate model for simultaneous studies of exercise, skeletal morphology, and energy physiology.
