Electron microscopy studies of papillary interstitial granules in normal human kidneys

The papillae of five kidneys from four heart-beating cadaver donors (one child and three young adults) were studied using electron microscopy (EM) technique. The kidneys were made available for EM study after they were found unsuitable for transplantation owing to low antigen match. All papillae had interstitial cells (IC), stellate processes, and intracellular and free granules. The three types of granules observed were (1) homogeneously dark, (2) gray and (3) layered; the free (outside the IC) granules were identical to the granules within the IC. The child kidney had more IC but fewer granules than the adult kidneys. The granules are ultrastructurally identical to those found in the rat renal papilla. Since rat renal papillary granules have been implicated as the source of renal vasodepressor substance(s), this ultrastructural resemblance suggests that human papillary interstitial granules likewise may be the source renal vasodepressor substance.