INTESTINAL CAPILLARIES II. Structural Effects of EDTA and Histamine

Perfusion of the fenestrated capillaries of the intestinal mucosa of the rat with 0.05-0 .1 M EDTA removes the diaphragms of the endothelial cells and detaches these cells from one another and from the basement membrane . The latter, even when completely denuded, retains effectively particles of 340 A (average) diameter. Perfusion with histamine (1 μg/ml) results in partial removal of fenestral diaphragms, occasional detachment of the endothelium from the basement membrane, and fecal separation of endothelial intercellular junctions . In a previous paper, we have shown that horseradish peroxidase and ferritin, used as probe molecules for the small and large pore system, respectively, leave the capillaries of the intestinal mucosa through the fenestrae of the endothelium (1) . Since these fenestrae, usually provided with an aperture or diaphragm (2-4), appear to be important pathways for plasma-interstitial fluid exchanges, we decided to investigate their response to agents known to affect capillary permeability such as EDTA' (5, 6) and histamine (7, 8) .