Adipose tissue lipolytic activity and urinary catecholamine excretion in cold-acclimated piglets

Abstract

This study was designed to investigate the effect of chronic cold exposure (12 degrees C for 3 weeks) on catecholamine production and noradrenaline-induced lipolytic rate to further describe thermoregulatory mechanisms in 5- to 8-week-old pigs. Lipolytic activity in white adipose tissue was assessed in vitro while catecholamine production was estimated by measuring noradrenaline, adrenaline, and dopamine levels in 24-h urine samples. Animals were fed ad libitum and food intake was 20% greater in the cold. In control piglets maintained in a 23 degrees C environment, the addition of increasing amounts of noradrenaline (10(-6), 10(-5), 10(-4) M) stimulates lipolysis (p less than 0.05) and enhances the basal lipolytic rate (5.4 mu equiv. fatty acids.120 min-1.g-1 tissue) by 2.5-, 2.7-, and 3.9-fold, respectively. Three weeks of cold acclimation had no effect on basal lipolytic rate but increased significantly noradrenaline responsiveness: incubation of subcutaneous white fat in the presence of 10(-4) M noradrenaline does increase the basal lipolytic rate by sixfold. Noradrenaline effects were maximally activated by theophylline. Daily dopamine and noradrenaline excretions (3-10 micrograms/24 h) were increased significantly (up to eightfold) after 10 days of cold acclimation. By contrast, adrenaline excretion was quite low (0.6-1.6 micrograms/24 h) and showed no significant variation with time. It is likely that these hormonal and biochemical modifications play a prominent part in the mechanism of cold acclimation in the piglet. Their significance in the development of shivering and nonshivering thermogenesis is discussed in relation to the supply of energy substrates to the fatty acid utilizing tissues and to the possible uncoupling effect of free fatty acids.