Ultrastructure of the interstitium in the rabbit kidney

Kidneys from six male New Zealand white rabbits were fixed by perfusion, and the interstitium of all zones was studied by light and electron microscopy. The volume and amount of the basic components varied not only between cortex and medulla, but within each zone itself. Two main cell types were found in the cortical interstitium, the first appeared to be morphologically identical with a fibroblast, although it contained frequent surface depressions. The second cell type was of the mononuclear series, the most frequent of which was characterized by abundant free ribosomes and was frequently wrapped by processes of fibroblasts. Although collagenous fibrils, basement membrane‐like material, and flocculent electron‐dense material have previously been described in the interstitium of other animal species, this paper describes the presence and distribution of microfibrils approximately 150 Å in diameter with electron‐lucent cores throughout the entire kidney interstitium and discusses the distribution of globular deposits which may represent glycosaminoglycans in the various zones of the kidney.