Abstract
The histochemical distribution of the succinic dehydrogenase system, DPN diaphorase and TPN diaphorase has been studied in the rat kidney. The staining pattern for each enzyme shows a highly reproducible and distinctly different zonal distribution in the cortex and medulla and a corresponding regional distribution along the course of individual nephrons. With these methods, virtually all the different segments of the nephron can be sharply delineated and identified.
Collecting ducts in the papilla, unstained with the succinate method, are well stained with DPN and TPN diaphorase. TPN diaphorase gives good staining of the thin limbs of Henle which are so difficult to demonstrate by other methods.
With the succinate system and DPN diaphorase, the thin limbs of Henle are unstained, but the thick ascending limbs stain heavily. This accounts for the sharp demarcation in staining seems between the outer medullary zone and the papilla. It is interesting that, with the succinate system, the collecting ducts show an abrupt cessation of staining at the same level.
Vascular endothelium and glomeruli show delicate staining with both diaphorases but not with succinate. Similarly, smooth muscle and the epithelium of the renal pelvis are stained by the diaphorase methods, but poorly, if at all, with succinate.
A distinct inner non-glomerular zone of the cortex is present in the rat and mouse kidney and is composed principally of coiled terminal portions of proximal convoluted tubules. In these rodents, the terminal segment of the proximal convoluted tubule is not straight and no distinct medullary rays are present. The staining of the inner cortical zone is distinctively different by all three methods from the staining of the outer zone which contains the first portion of of the proximal convoluted tubule. This furnishes additional evidence for a functional division of labor in the proximal convoluted tubule.
In the papilla, fusiform cells of unknown function are present in parallel formations, oriented at right angles to the direction of the tubules. These are well demonstrated in the rat kidney by TPN diaphorase and are found to be even more abundant in a desert rodent, the kangaroo rat. Should these cells prove to have a contractile function, they might play a role in the regulation of urinary volume.
Studies of the chemical anatomy of the kidney using these enzyme methods offers further evidence that the nephron is divisible into more than the conventional number of functional segments.