Tracer kinetic studies on in vivo fatty acid metabolism in white adipose tissue of well-fed and starving newborn rabbits during acute or prolonged exposure to cold.

Pool size (M), and specific radioactivities (SA) of lipids of white adipose tissue (WAT), as well as the flow rates (ms) of free fatty acids (FFA) from plasma into WAT were studied by injecting 14C-1-palmitate (20.10(6) cpm/100 g body weight) into 7-day-old rabbits reared in a thermoneutral (Group I) or a cold environment (Group II) or subjected to starvation at an ambient temperature (Ta) of 35 degrees C (Group III) or at Ta 20 degrees C (Group IV). Experiments were carried out at Ta 20 degrees C in all four groups of rabbits. The pool size of esterified and non-esterified fatty acids of WAT was reduced in both the well-fed animals raised in the cold and in the starving ones. The SA of tissue FFA and phospholipid fatty acid (PL-FA) was highest in Group III and Group IV indicating an increased FFA metabolism of WAT in animals subjected to starvation prior to acute exposure to cold. The flow rate (ms) of FFA between plasma and WAT increased twofold in Group IV but remained about one fifth that of the ms between plasma and brown adipose tissue (BAT) indicating that the contribution of WAT to cold-induced calorigenesis of the whole animal must be regarded as of secondary importance.