Genetic relation of life span to metabolic rate for inbred mouse strains and their hybrids.

Average life spans were estimated for the male progeny from 21 of the 25 possible matings of 5 inbred mouse strains. Oxygen consumption was measured in an open system over a 48-hour interval. Resting metabolism, Mre, and average metabolism, Mav, were determined at 6-8 months of age, and at 24-34 months. Body weight, W, was determined at the time metabolism was measured. Life span, L, is negatively correlated with Mre and Mav, and positively correlated with W at both ages of measurement. This is in accord with the metabolic wear factor that had previously been established among 85 different species of mammals. A new metabolism variable, the energy partition coefficient, defined as the ratio of average to resting metabolic rate, Mav/Mre, has a parabolic relation to body weight, i.e., is maximal at an intermediate body size. The squared body weight deviation in turn has a negative correlation with life span. The correlation of L with Mav/Mre is positive, as expected, but not significant. These data suggest the existence of a longevity factor dependent on the partition of energy between the phasic metabolism of activity and the continuous maintenance metabolism.