Effects of Escherichia coli endotoxin on structure and permeability of myocardial capillaries.

A study was carried out to investigate changes in myocardial capillaries induced by endotoxin, in order to clarify the pathogenesis of myocardial damage in endotoxemia. Wistar rats were injected intraperitoneally with 100 mg/kg Escherichia coli lipopolysaccharide and then sacrificed at 1, 2, 3,4, 5, 6, 8, and 24 h after injection. The myocardium was observed by electron microscopy with histochemistry using horseradish peroxidase and immunocytochemistry for Na+, K(+)-ATPase/TPase. The earliest evident endothelial alterations were swelling, increased numbers of pinocytotic vesicles, and formation of cytoplasmic projections. Interstitial edema and focal detachment of the endothelial cells from the basement membrane occurred with time. Vascular permeability was increased after endotoxin injection. Activity of Na+, K(+)-ATPase was reduced on the plasma membrane of the endothelial cells. It is concluded that endotoxin induces structural and enzymatic changes in the myocardial capillary endothelium and an increase of capillary permeability.