Microcalorimetric studies on the total metabolic activity of fat cells

We have applied microcalorimetry to the study of total cellular metabolic activity by direct registration of heat production from small samples of isolated fat cells. The cellular heat production is rapidly influenced by addition of hormones and substrates in vitro; e.g. glucose and insulin increases heat production two- to three-fold. The perirenal fat had the highest heat production. Fat cell thermogenesis decreases with age (and increasing mean fat cell size) of the rat. Obese patients had low heat production measured in gluteal adipocytes; the cellular thermogenesis increased, but did not fully normalize, on weight reduction. In combination with measurements of substrate and metabolite concentrations, microcalorimetry allows a detailed quantitative assessment of energy metabolism in the cell, which makes it a powerful tool for the study of adipose tissue metabolism under physiological and pathophysiological conditions.