BODY-SIZE ALLOMETRY OF MAMMALIAN BLOOD HEAT OUTPUT AS ASSESSED BY MICROCALORIMETRY

The heat output of heparinized blood samples from seven mammalian spec ies (hamster, rat, hedgehog, dog, swine, human and sheep) was determin ed by ampoule microcalorimetry and related to body mass. Typical micro calorimetric records consist of an initial plateau and a terminal decl ine of metabolic rate. A decrease in the plateau heat output with incr easing body mass was found, corresponding to the allometric relationsh ip between specific basal metabolic rate and body mass. Moreover, the duration of the plateau was nearly reciprocal to the level of heat out put, indicating a relatively constant ''energy content'' of blood samp les which in smaller species, due to their higher thermal power, is ut ilized faster than in larger ones. The presence of scaling effects in a physiological cell suspension may elucidate-the still unknown regula tory mechanisms of metabolic size allometry.