The importance of liver in normal and silicotic lung-lipid homeostasis. 1. Phospholipids

We studied the total content, concentration and specific activity of phospholipids (PL) in the lung, liver and serum of rats intratracheally injected with silica or saline. Intact rats served as controls. The animals were sacrificed at four time intervals ranging from 6 to 144 hours. The presented data are based on analyses of 87 rat lungs. Instillation of silica into rat lungs results in a significant increase of PL content in the lung 72 and 144 hours later. These changes, when correlated with PL changes in the serum and liver, indicate that the lung signals the liver to mobilize its PL which are then deposited in the lung. Injections of silica into the lung promote phospholipidgenesis in the liver. The de novo formed PL are then mobilized to the lung via the serum. Saline injection into rat lungs results in increased phospholipidgenesis only in the lung while liver PL content as well as concentration is significantly decreased; however, the synthesis of liver PL is not significantly increased. The lung thus communicates with the liver, causing the liver to respond with phospholipidgenesis and the mobilization of liver phospholipids.