Brown adipose tissue and carnitine in cold-adapted rats

Cold-adapted (CA) and warm-adapted (WA) rats (5 and 28 degrees C) were infused with noradrenaline (4 microgram.kg-1.min-1) for 15 min. Blood was collected from Sulzer's vein coming from brown adipose tissue and analyzed for total carnitine, free carnitine, and beta-hydroxybutyrate content, before and up to 45 min after the infusion. Acylcarnitine (total minus free carnitine) levels increased more and total carnitine levels decreased more in the CA group than in the WA group. beta-Hydroxybutyrate content increased to the same extent (from about 0.16 to 0.8 mM) in both groups. Brown fat was found not to release carnitine into the circulation after NA infusion. Twenty minutes after the end of the infusion brown fat retained both ketones and acylcarnitine in the CA rats only.