Fine structure of the rat renal papilla

Abstract

The fine structure of the rat renal papilla was studied after fixation with various fixative solutions and by using three modes of fixative application: immersion, vascular perfusion and injection of fixative into the renal pelvis. The morphology of the following was described: thin limbs of Henle's loop, collecting ducts, capillaries, interstitial cells, and interstitium. Several previously undescribed features were seen. Two types of capillaries were identified on the basis of their fine structure. Regions identified as limbs of Henle had at least two types of mural structure differing in degree of cellular interdigitation. In addition, numerous projections were seen extending from the basal cytoplasm of capillary endothelium and collecting duct epithelium through the basement membrane into the interstitium.It has long been assumed that the renal papilla is important in the production of concentrated urine (Marshall, '34). Though the exact mechanisms involved are still the subject of considerable debate, several groups of workers (Wirz and co-workers, '51; Wirz, '53; and others) hypothesized that the papilla was the site of a countercurrent multiplier, a counter-current exchanger and an osmotic exchanger. The loop of Henle is presumed to function as the counter-current multiplier by creating an increasing gradient of solute concentration from the cortex to the papillary tip. When the collecting duct (an osmotic exchanger) passes through the concentrated interstitium of this region, water leaves the tubular lumen resulting in the production of hypertonic urine. The capillaries form a counter-current exchange system allowing blood flow without abolition of the gradient. Micropuncture studies by Gottschalk and Mylle ('59) were consistent with this hypothesis. The majority of other physiological experiments are also consonant with the counter-current hypothesis, but some contradictory experiments have been reported '58; and Marsh and Solomon, '65).Although a few reports concerning selected aspects of papillary fine structure have been published (Rhodin, '58a,b, '62, '63; Sakaguchi and Suzuki, '58 study of all the structures in the papilla seems warranted as a basis for our morphological studies of this region in water diuresis and antidiuresis. MATERIALS AND METHODSSixteen Sprague-Dawley and 14 Charles River male and female rats, weighing 175-300 gm were used in this experiment. The rats were allowed access to food and water at will until the time of sacrifice.The animals were anesthetized with pentobarbital and opened with a mid-ventral incision. Kidneys were fixed by three methods.( 1 ) The kidneys were removed and small (-1 mm) slices or pieces immersed in the fixative solutions for various time intervals. (2) At the time of laparotomy with the blood supply still intact, 5 ml of fixative solution were injected into the renal pelvis for a period of approximately five minutes with a needle and syringe. The fixative could be seen to move down the ureter into the bladder if the needle was in the renal pel...

Comparative Analysis of the Concentration of Injected Horseradish Peroxidase in Cytoplasmic Granules of the Kidney Cortex, in the Blood, Urine, and Liver

“…The ability of interstitial cells in the renal medulla to ingest peroxidase (Figs. 8 and 9) is in agreement with observations by other investigators (1,9), who reported the phagocytic ability of these cells . An increase in the number of lysosome-like granules in the interstitial cells after K+ depletion has also been described (9,21) .…”

“…In experiments in which rats weighing 60, 160, 240, and 400 g received the same dose of 62,500 units of peroxidase per 100 g body weight, the proportion of peroxidase found in homogenates of the kidney cortex of the rats weighing 60 and 160 g each was 1 .6% of the injected amount (specific activity, 8 …”

Proliferation and Migration of Label-Retaining Cells of the Kidney Papilla

“…It is unresolved whether these two cell populations are related, but detailed morphologic observations of collecting duct cells found numerous projections extending from the basal part of the cell's cytoplasm through the duct's basement membrane into the papillary interstitium 30 and suggest that collecting duct cells can migrate into the interstitium. 31 Interestingly, we also found that interstitial LRC are nestin positive, a protein of the intermediate filament family originally found in neuroepithelial stem cells (see reference 32 for a review).…”

Randall’s plaque of patients with nephrolithiasis begins in basement membranes of thin loops of Henle

“…Thin-limb basement membrane is unusually thick and is composed of collagen with considerable mucopolysaccharides (21). Such a matrix offers electrostatically charged ionic sites that can attract calcium and phosphate.…”