Effects of Fasting and Refeeding in the Rat on Adipocyte Metabolic Functions and Response to Insulin

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Abstract
Glucose metabolism, lipolysis, intracellular free fatty acids (IFFA) and response to insulin were determined in epididymal fat cells of mature rats before and after 2 days of fasting, and following refeeding ad libitum for intervals up to 20 days. Fasting for 2 days produced a significant decline in body weight (-18% from control values), weight of the epididymal fat pads (-21%) and mean fat-cell size (-32%); these changes returned to control levels after 3 to 5 days of refeeding. The metabolic data show that basal glucose metabolism to CO2 and lipids, expressed on a per fat cell basis, declined by 57% with fasting, returned to control values 2 days after refeeding, and reached higher values at 5 to 10 days of refeeding. The insulin-stimulated glucose metabolism diminished markedly with fasting (to 33% of control values) and then rose to higher values (approximately 150% of control) in 3 to 10 days of refeeding. In contrast, the rate of lipolysis doubled with fasting, reached highest levels (500% of control) after 1 day of refeeding, and then progressively returned to control values. The IFFA levels were found to decrease 35% with fasting and to return to control values 3 to 5 days after refeeding. These findings underscore the value of expressing adipose tissue metabolic data on the basis of fat-cell number to uncover marked, novel, and protracted metabolic alterations produced in animals by a short period of food deprivation followed by resumption of ad libitum feeding.