Utilization of pyruvate, alanine and glutamate by isolated fat cells and their effects on glycerol metabolism.

To study the metabolic interactions of different substrates in adipose tissue in vitro, isolated fat cells from fed rats were incubated in medium containing either (U-14C)-pyruvate, L-(U-14C)-alanine, L-(U-14C)-glutamate or (1(-14)C)-glycerol, and supplemented or not with 5 mM glucose or with non-radioactive pyruvate, alanine or glutamate (2 or 10 mM). The utilization of pyruvate for CO2 or fatty acid formation was greater than that of alanine and glutamate, both in the absence and presence of glucose. Glucose enhanced the formation of fatty acids from all the labelled substrates, decreased the synthesis of glyceride glycerol from pyruvate and glycerol, and enhanced it from alanine and glutamate. Pyruvate and glutamate enhanced the utilization of glycerol by the adipocytes and these effects were significantly reduced in the presence of glucose. Thus, the metabolic fate of the glycerol taken up by the cells varied according to the nature of the available substrates.