SIZE EFFECTS ON METABOLIC-RATE IN CELL, TISSUE, AND BODY CALORIMETRY

Size effects on metabolic rate include the effects of body size (biolo gical) and sample size (methodological) and are to be found in cell, t issue, and body calorimetry. The biological size effect, known as Klei ber's rule and consisting of a metabolic reduction with increasing bod y mass, is demonstrated by the size relationship of blood heat output in several mammalian species (cellular level) and by the differing met abolic behaviour of cardioplegic rat and dog heart samples (tissue lev el). The methodological size effect, known as the crowding effect and consisting of a metabolic decrease with increasing sample size, is dem onstrated in human renal carcinoma cells (cellular level) and ischemic rat liver samples (tissue level) and is explained by a simple mathema tical simulation. With respect to body calorimetry, it is stressed tha t metabolic size allometry may be temporarily inactivated in special b iological adaptations (neonatal period, mammalian hibernation), and we ight correction of metabolic rates may produce methodological problems when mass differences are mainly due to varying body fat content (cir cannual rhythms). In conclusion, careful size standardization is a pre requisite of comparability in biomedical calorimetry.