Free fatty acid turnover and oxygen consumption. Effects of noradrenaline in nonfasted and nonanesthetized cold-adapted rats

Abstract

The effects of a 3-h noradrenaline (NA) infusion (1.5 μg kg−1 min−1) on the O2 consumption, the respiratory quotient (RQ), the concentration of plasma free fatty acids (FFA), and the rates of appearance (Ra) and disappearance (Rd) of plasma FFA were studied in nonfasted and nonanesthetized control and cold-adapted rats. To calculate the Ra FFA and Rd FFA, [1-14C]palmitate complexed to albumin was infused as a tracer. The concentrations of glucose and lactate in blood were also determined before and during the NA infusion. The enhanced O2 consumption produced by NA in cold-adapted rats was associated with a decreased RQ. The Ra FFA and Rd FFA were more enhanced by NA in cold-adapted than in control rats whereas the plasma FFA concentration was less elevated in cold-adapted rats. The blood lactate was barely increased by the NA infusion in cold-adapted rats and was not modified in control rats. Blood glucose was increased by NA in both control and cold-adapted rats but to a greater extent in control rats during the last 90 min of NA infusion. These results suggest that the enhanced calorigenic response to NA observed in nonfasted and nonanesthetized cold-adapted rats is related, at least partly, to an enhanced lipid metabolism; the RQ is low and Ra FFA and Rd FFA are greatly increased. However, the contribution of other energetic substrates like glucose will also be investigated in further studies.