RELATIONSHIP BETWEEN ENDOTHELIAL-CELL TURNOVER AND PERMEABILITY TO HORSERADISH-PEROXIDASE

The quantitative relations between cell turnover (cell mitosis and dea th) and macromolecular leakage were studied at the level of individual endothelial cells (ECs) in the thoracic aortae of 32 adult male Sprag ue-Dawley rats. The experiments were performed on en face preparations of aortic specimens obtained 1, 3, 5 or 10 min after the intravenous administration of horseradish peroxidase (HRP). Mitotic ECs were ident ified by hematoxylin nuclear staining; dying or dead ECs containing cy toplasmic immunoglobulin G were detected by indirect immunocytochemist ry and endothelial leakages to HRP were visualized by light microscopy . The number and size of HRP spots increased with time and the spots f used to form large brown areas in 10 min. Quantitative data on the con tributions of EC mitosis and EC death to the transendothelial leakage of HRP were obtained in the same animals. Although mitotic ECs (0.01%) and dying ECs (0.1%) were infrequent in occurrence, the great majorit y (over 90%) of these ECs were associated with focal HRP uptake. These mitotic and dying ECs, however, accounted for only 17% of the total l eakage sites indicating that significant leakage of the 4-5 nm HRP als o occurs in normal ECs not morphologically identified as being in mito sis or death. The percentages of leaky spots attributable to mitosis o r cell death were greater for the 6 nm albumin and the 22 Mn low densi ty lipoprotein (LDL) which probably cannot traverse the normal junctio ns and use the leaky junctions during cell turnover as the major pathw ay. (C) 1997 Elsevier Science Ireland Ltd.