Outflow segment of the efferent arteriole of the rat glomerulus investigated by in vivo and electron microscopy.

Abstract

In previous intravital microscopic studies of the hydronephrotic split kidney a narrow segment in the efferent arteriole at its origin from the glomerulus was observed. In the present study in vivo techniques were combined with transmission electron microscopy of thin sections to investigate the structural basis for the luminal narrowing. At the point where the efferent arteriole leaves Bowman's capsule prominent endothelial cells were found to bulge into the lumen of the vessel. These cells participate in the overall narrowing of the lumen at this site and appear to be responsible for the in vivo picture. However, the principal basis for the narrowing seems to be an extrinsic constriction of the vessel, possibly by extraglomerular mesangial cells located at the exit level. It is suggested that the outflow portion of the efferent arteriole may be an important site of control of glomerular blood flow.