Further evidence of tubular blockage after acute ischemic renal failure in Tupaia belangeri and rats

Tree shrews at the German Primate Center

Abstract. For many years, Tupaia (family Tupaiidae), most commonly known as tree shrews, have been studied almost exclusively by zoologists resulting in a controversial debate on their taxonomic status among mammals. Today, tree shrews are placed in the order Scandentia; they are valuable, widely accepted and increasingly used model animals as an alternative to rodents and non-human primates in biomedical research. After a brief description on how tree shrews entered science and their taxonomic odyssey, the present article describes the history of the tree shrew (Tupaia belangeri) colony at the German Primate Center and selected aspects of our work with special emphasis on the psychosocial stress model in these animals.

Morphology of norepinephrine-induced acute renal failure in the dog

The 40-minute infusion of norepinephrine (NE) into the renal artery of dogs produces a reversible ischemic model of acute renal failure. While the physiology of this model has been extensively studied, no complete description of the pathology exists. This study uses light microscopy and transmission electron microscopy to describe and quantitate the structural and ultrastructural changes which occur in the kidneys of dogs 1, 3, and 24 hours after the intrarenal infusion of 0.75 mg/kg/minute of NE. One hour after a 40-minute NE infusion the majority of convoluted and straight proximal tubules showed apical blebs, loss of brush border, microvillar whorl formation, and mitochondrial condensation and high-amplitude swelling with flocculent densities. Necrotic cells were occasionally seen at 1 hour. The injury was progressive after 3 hours and by 24 hours animals had either complete or partial patchy necrosis of all regions of the proximal tubule. The percentages of injured and necrotic proximal tubules in outer, mid-, and inner cortical regions are presented. We conclude that the extent and pattern of injury seen after NE infusion differs significantly from the renal artery clamping model of ischemia.

Glomerular filtration and tubular reabsorption during anuria in postischemic acute renal failure

Complete occlusion of the left renal artery for 60 min in the rat produced anuric acute renal failure after 1 day. Using fluorescence microscopy, a television system combined with double slit densitometry, and micropuncture techniques, tubular pressure and tubular flow rates were determined in different segments of superficial nephrons. Intratubular pressures in proximal convolutions of the postischemic kidney were largely heterogeneous due to abnormally increased flow resistance in proximal tubules which were filled with loose obstructive material. Proximal tubular pressure in the control kidney was independent of the site of its measurement and had a mean value of 14.1 mm Hg. In the postischemic kidney pressure decreased gradually along the proximal tubule, its value in the early and late segments being 16.3 and 9.7 mm Hg, respectively. Low pressure in late proximal convolutions excludes a significant flow impediment due to obstruction in more distal segments. The mean nephron filtration rate (SNGFR) obtained by extrapolation of tubular flow data was 62% of the control value, whereas tubular reabsorption was estimated to be 50% above normal. Reduced SNGFR and increased outflux caused a total reabsorption of tubular fluid within 60% of proximal convoluted tubule length. The partial reduction of SNGFR can be explained by increased pressure in early proximal convolutions and reduced glomerular plasma flow known for these kidneys, without postulating a change in glomerular permeability. Tubular obstruction and increased passive outflux in proximal tubules due to cellular damage appear to be crucial mechanisms responsible for the loss of renal function in this model of acute renal failure.

Hydronephrosis: a new method to visualize vas afferens, efferens, and glomerular network

We have developed a new preparation for in vivo visualization of the glomerular microcirculation, the vas afferens and the vas efferens. This preparation utilizes postischemic hydronephrosis (PIH) to destroy the renal tubular system while preserving a portion of the cortex. In this preparation, glomeruli and associated vasculature remained intact. Observations can be made with either incident light or transillumination. The inner diameter of the vas afferens, measured within 50 microns of the glomerular vascular pole, was 7.9 +/- 0.5 microns (N = 12; SEM) while that of the vas efferens was 7.7 +/- 0.5 microns (N = 12). Both vessels were narrower adjacent to the glomerulus; minimal diameters in this region were 4.5 +/- 0.5 microns (N = 10) and 4.3 +/- 0.5 microns (N = 11), respectively. A specialized round cell, which may act as a sphincter, was seen in the vas efferens. In a second series of experiments, blood velocity was measured in the vas afferens and efferens about 100 microns from the vascular pole. Mean control velocities at these sites were 5.9 +/- 0.9 (N = 14) and 4.6 +/- 1.3 (N = 9) mm X sec-1, respectively; diameters at these same sites were 10.3 +/- 0.6 microns and 11.2 +/- 0.7. During angiotensin II infusion (first series, 0.2 to 0.4 micrograms X min-1 X kg-1, i.v.) the vas efferens in the vicinity of the glomerulus constricted by 22% whereas the corresponding vas afferens showed no consistent response. During angiotensin II infusion, the filtration fraction (GFR/RPF) may, therefore, be elevated by an increased resistance in the vas efferens, particularly at the outflow point of the glomerulus. In the second series of experiments higher dosages of angiotensin II caused vasoconstriction of both vessels, especially at sites more distant from the glomerulus. Furthermore, the new approach is suitable for observing the flow direction within single capillaries of one third to one half of the glomerulus. Therefore, for the first time it is possible to determine the real flow direction in a three-dimensional way.

Renal hemodynamics and oxygen consumption during postischemic acute renal failure in the rat

Acute renal failure in the rat was induced by occluding the left renal artery for 1 hour. The kidneys were examined 1, 3, 10, and 40 days after temporary ischemia. Inulin clearance was essentially zero in oligoanuric kidneys on days 1 and 3, and regained 14% and 63% of the control value on days 10 and 40, respectively. Mean cortical blood flow remained almost constant at 75% of control up to day 10 and normalized subsequently on day 40. Renal oxygen consumption during anuria on days 1 and 3 was 53% and 46% of the control value and increased thereafter concurrently with the restoration of renal function. With a single linear correlation being assumed to exist between sodium reabsorption and oxygen consumption for all kidneys, the sodium reabsorption and oxygen consumption for all kidneys, the sodium transport estimated from oxygen consumption on day 1 was about 40% of control value. The difference between the sodium transport calculated from oxygen consumption and that from inulin clearance decreased with time in the recovery phase. The results indicate only a partial reduction of GFR due to the reduced blood flow in this model. The data are consistent with the hypothesis that tubular leakage and tubular obstruction play an important role in the loss of renal function during the manifestation of acute renal failure.