Glycerol and nonesterified fatty acid metabolism in human muscle and adipose tissue in vivo

To determine the relationship between glycerol and nonesterified fatty acid (NEFA) release from adipose tissue, and to test whether forearm muscle and abdominal adipose tissue are capable of extracting these two lipolytic products from the circulation, 13 male subjects were studied after an overnight fast during combined infusion of radiolabeled palmitate and glycerol. Blood samples were taken from a radial artery, a deep forearm vein, and a superficial abdominal vein before and during a 2-h infusion of glucose at approximately 7 mg. kg-1. min-1. The ratio of the appearance rates of total NEFA to glycerol was approximately 3/1 during the baseline period but decreased to 1.3/1 during glucose infusion. There was significant extraction of both glycerol and NEFA by forearm muscle. In contrast, there was no apparent uptake of glycerol by adipose tissue. Adipose tissue NEFA uptake was undetectable during the baseline period but became significant during glucose infusion. These data indicate that there is very little to no in situ reesterification of NEFA in adipose tissue after an overnight fast. During glucose infusion, there was apparently a relative increase in the fraction of glycerol derived from the action of lipoprotein lipase and an increase in reesterification in situ.