TISSUE RESPIRATION, GROWTH, AND BASAL METABOLISM

Abstract

The relation between tissue respiration and body size is studied in 7 organs (heart, lungs, liver, kidney, brain, diaphragm, thymus) of rats, of 9 to 392 g. body wt. QO2 values for the organs mentioned, and their variations with body size are descr. and the results treated statistically. Some data on QO2 of fetuses and fetal organs are also given. The diaphragm is the only organ showing a high correlation between rate of tissue respiration and body size, while the other organs do not show differences in QO2 cor-responding to the decline in wt.-specific metabolic rate of the entire animals. In liver and thymus, a break in the regression line of QO2 against body wt. can be found which corresponds to a change of other physiological characteristics at the same period (about 100 g. wt.). Intraspecific and interspecific size dependence of tissue respiration are compared. The current theories on the systematic decline of wt.-specific metabolic rate with increasing body size (surface and 3/4-power rule) are discussed in the light of the expts. The decline in wt.-specific metabolic rate appears to be controlled by factors lying in the organism as a whole.