Glucose, acetate, and lactate metabolism in perirenal adipose tissue of fetal and newborn calves.

Rates of utilization of glucose, acetate, and lactate and activities of selected enzymes were determined in vitro to characterize the nature of lipogenesis and metabolite utilization in perirenal adipose tissue from 6- to 7-month old fetal and 3- to 4-h-old unsuckled newborn calves. Contribution of the pentose phosphate cycle to glucose metabolism was estimated using specifically labeled glucose. Rates of fatty acid synthesis from all three substrates and oxidation of glucose were much greater in fetal than in newborn adipose tissue. In fetal adipose tissue, acetate and lactate were major sources of carbon for fatty acid synthesis; glucose functioned mainly by metabolism via the pentose phosphate cycle to provide reducing equivalents for fatty acid synthesis and by incorporation into glyceride glycerol for fatty acid esterification. Pentose phosphate cycle contributed 58 and 12% to glucose metabolism in adipose tissue of fetal and newborn calves, respectively. Adipose tissue metabolism of newborn calves was characterized by greatly depressed rates of fatty acid synthesis despite high enzyme activities and elevated rates of glyceride glycerol synthesis.