Absence of increased oxygen consumption in brown adipose tissue of rats exhibiting "cafeteria" diet-induced thermogenesis

Young male Sprague-Dawley rats were induced to overeat (approximately 45%) by provision of a "cafeteria" (CAF) diet of palatable human foods. Normophagic rats fed a commercial chow or a semisynthetic diet served as controls. The CAF rats exhibited (a) the reduced food efficiency and the propranolol-inhibitable elevation in resting metabolic rate (resting VO2) that are indicative of a facultative diet-induced thermogenesis (DIT) by which excess energy gain is resisted, and (b) certain changes in brown adipose tissue (BAT) that are among those taken as evidence for BAT as the effector of DIT, e.g., increased protein content and increased mitochondrial binding of GDP. To assess directly and quantitatively the contribution by BAT to the elevation in VO2 (apparent DIT) of the CAF rats, BAT O2 consumption was determined (Fick principle) from measurements of tissue blood flow (microsphere method) and the arteriovenous difference in blood O2 across interscapular BAT (IBAT). To obtain the measurements, the animals were fitted under halothane anesthesia with vascular cannulas for intraventricular injection of microspheres and sampling of arterial blood and the venous effluent of IBAT. After recovery from anesthesia and rewarming to normal body temperature the animals were placed singly in a temperature-controlled metabolic chamber and the measurements, which also included determination of resting VO2, were made 1.5-2 h later about 11:30 h. As determined from measurements made at 28 degrees C (thermoneutrality) mean values of resting VO2 for the cannulated rats were unchanged from those of intact (unoperated) CAF or control rats.(ABSTRACT TRUNCATED AT 250 WORDS)