Pulmonary arterial-venous differences in lipids and lipid metabolites

This study was designed to reevaluate the effectiveness of the lungs in taking up lipids from the blood, and to establish whether or not the blood triglycerides so extracted are metabolized. 8 normal human males were studied. With the subject fasting and supine, a percutaneous catheter was placed in the pulmonary artery, another in the superior vena cava, and a third in the brachial artery. Samples of mixed venous and arterial blood were drawn by syringe from the pulmonary and brachial arteries, respectively. Infusion of a triglyceride emulsion (20% Intralipid) into the superior vena cava was begun at 4.7 ml/min. After 12 min of infusion, mixed venous and arterial samples were taken and infusion was discontinued. 15 min following termination of infusion, blood samples were again drawn. Analysis showed the lungs to be retaining about 25% of available triglyceride. Cholesterol concentration was unaffected. Arterial-venous differences in glycerol and free fatty acid were insignificant, suggesting no metabolism of triglyceride by lungs. The lungs apparently serve as a mechanical screen to triglyceride.