Effects of adrenaline and noradrenaline on clearance of triacylglycerol-rich lipoproteins from plasma: studies with chylomicron-like lipid emulsions in rats.

1. Adrenaline was infused intravenously in rats during the clearance from plasma of an injected lipid emulsion designed to model chylomicrons and the triacylglycerol-rich plasma lipoproteins. The clearance rates of emulsion radiolabelled triolein (TO) and cholesteryl oleate (CO) were both increased, suggesting that hydrolysis of lipoprotein triglycerides and clearance of remnants from plasma were increased. The distribution of radiolabels in tissues showed more TO in skeletal and cardiac muscle after adrenaline, while more CO was found in liver compared with controls. Lesser amounts of both labels were found in the spleens of treated rats. 2. In a similar experiment with noradrenaline, the clearance rate of emulsion CO was decreased. The removal of CO was retarded more than that of emulsion TO, which was not significantly affected, and CO label recovered in liver was significantly decreased, suggesting that the removal of remnants from plasma was slowed after noradrenaline. In experiments in which noradrenaline was infused continuously for 1 week the clearances of emulsion CO and TO were both reduced. 3. Our findings suggest possible connections between plasma catecholamines and the development of arteriosclerosis, in view of the atherogenicity of remnants of the triacylglycerol-rich plasma lipoproteins. Yet to be established is whether the linkage we have found between lipoprotein clearance, adrenaline and noradrenaline contributes to the atherogenic effects of chronic stress and for the protective effects of exercise.