[Pathomorphological studies on arterial cushion. 1. Rat normal kidney]

The present studies are an attempt to elucidate the vulnerability of focal glomerular sclerosis (FGS). The distribution and morphology of the arterial cushions were studied in rat renal arteries by light microscopy, transmission electron microscopy and scanning electron microscopy (SEM) using of the renal vascular casts. The arterial cushions were observed at a region of the branching arteries from the arcuate arteries and the interlobular arteries. They were extensively demonstrated mainly in the mid cortex and juxtamedullary cortex by the serial sections, but not in the subcapsular cortex. The arterial cushions showed valve-like protrusions and consisted of three components, such as the endothelial cells, the smooth muscular cells and the interstitial ground substances, electron microscopically. The cushions are covered by the endothelial cells which often showed various variation in thickness. Also these had deep processes which elongate into the interior of the cushions. The cells of interior portions of the cushions were modified smooth muscular cells. These cells contained numerous myofibrils and a large number of scattered glycogen granules. No nerve fibers were seen within the cushions. The modified smooth muscular cells were embedded in a loose matrix (probably acid mucopolysaccharides) which contained strands of basement membrane like material. The cushions were observed on the wall of the arcuate and interlobular arteries in the cortex except for subcapsular cortex by SEM. They showed elongated indentation surrounding lumen of their arteries. These results of the observation, the cushion may be important factor for the regulation of blood flow in small arteries and arterioles. The disorder of autoregulation of interlobular arteries due to dysfunction of the cushions with anionic loss were assumed to be one of the important factor in progress to the glomerular sclerosis.