Hepatic uptake of albumin-bound substances: albumin receptor concept.

The single-pass hepatic uptake of long-chain fatty acids and other substances bound tightly to albumin in plasma is surprisingly efficient. Recent kinetic studies for several of these substances suggest that uptake is mediated primarily by direct interaction of the albumin-ligand complex with the hepatocyte surface rather than by the small fraction of unbound ligand, as has been generally believed. Furthermore, 125I-albumin has been found to bind specifically, saturably, and reversibly to isolated hepatocytes, adipocytes, and erythrocytes. Although the nature and possible regulation of these binding sites remain to be fully elucidated, the putative albumin receptor may play an important role in the bidirectional transfer of many classes of endogenous and exogenous substances between albumin and cells.