Giaja published a paper on the minimal energy consumption for life support with B. Maleš in 1921, showing that, as in poikilotherms, the energy consumption in homeotherms also depends on external temperature*. This paper is considered his first venture into studying hypothermia. In line with this study, in another paper in 1922 with B. Maleš, Giaja defines the oxygen consumption at normal and lethally high (40°C) external temperatures. He then introduced a parameter termed “peak metabolism” and defined its relationship to the classical basal metabolism and the dependence of both on various environmental factors. Thus, he defined peak metabolism as a counterpoint to basal metabolism – the limiting point of thermoregulation during fasting or in the cold. Giaja also introduced the “metabolic quotient”, or the ratio of peak to basal metabolism that defines caloric consumption. In 1925, he reported on the relationship between the loss of heat and basal metabolism as well as the role of some endocrine factors (insulin and adrenergics) in heat production.
During this period, Giaja also studied the effect of alcohol on the thermogenic potential of the organism and the influence of nutrition on metabolism. He established that fat in particular is mobilized for the production of additional heat. If glycogen serves as the immediate fuel, it must be mostly regenerated proportionally to its consumption on account of the fat. In 1928, he again revised the definition of basal metabolism, presenting it not as the minimum consumption necessary for life support but instead the sum of that minimum and an assumed limiting value adapted to the functional requirements of homeothermia.
Simultaneously, Giaja showed interest in hibernators. He hypothesized that hibernation could be a consequence of a lower peak metabolism, but showed that this was not the case since a hibernator such as the common hedgehog has a peak metabolism of the same amplitude as the other non-hibernating homeotherms.
Andjus PR, Stojilkovic SS, Cvijic G. Ivan Djaja (Jean Giaja) and the Belgrade School of Physiology. Physiol Res. 2011;60 Suppl 1:S1-13. Epub 2011 Jul 19. [link]