Increased capillary permeability in muscularis layer of rat intestine caused by kidney extract

Kidney extract and synthetic angiotensin II were injected into bilaterally nephrectomized rats in dosages capable of raising the mean arterial pressure by about 20 mmHg. Changes in ultrastructure and permeability for ferritin molecules were then examined in capillaries located in muscularis layer of the intestinal walls. Kidney extract with a high renin content was obtained from the renal cortex of rats by means of stepwise centrifugation methods. Animals injected with saline served as controls. In rats receiving kidney extract tissue edema was observed in the spaces around the blood and lymphatic capillaries. In these spaces ferritin molecules accumulated in high concentration indicating plasma protein leakage. Ferritin molecules within the endothelium were restricted within plasmalemmal vesicles, but were not found within interendothelial junctions or within the cytoplasmic matrix. Morphometric analysis of vesicular transport in the endothelial cells revealed a significant increase in labeling rate for the vesicles with ferritin molecules. These results suggest that the kidney extract contains substance(s) which increase capillary permeability for plasma proteins at least via increased vesicular transport, resulting in tissue edema.