June Mason

The early phase of experimental acute renal failure

Experiments were performed to determine whether furosemide, given in doses high enough to induce a strong diuresis and to inhibit the mechanism of tubuloglomerular feedback, offers any protection from acute renal failure induced by a nephrotoxin or ischaemia. Microperfusion of the loop of Henle revealed that a tubular furosemide concentration of 5·10−5 mol·l−1 was necessary to fully inhibit the tubuloglomerular feedback response to a raised sodium chloride concentration at the macula densa. The infusion of furosemide systemically to achieve such concentrations in the tubule resulted in an improvement in renal function when given before or after the nephrotoxin but was without effect when given before or after ischaemia. Measurements of furosemide concentrations in the urine, however, confirmed that sufficient amounts were applied to inhibit the feedback mechanism. It is concluded from this and similar studies that furosemide is only beneficial in models of acute renal failure with an obstructive or nephrotoxic pathogenesis, in which it acts by flushing out the noxious material and not by inhibiting the mechanism of tubuloglomerular feedback.

The early phase of experimental acute renal failure. III. Tubuloglomerular feedback

SummaryExperiments were designed to determine whether tubuloglomerular feedback, which modifies nephron filtration rate in response to alterations in the macula densa sodium chloride concentration, was still apparent in the initiation phase of various types of acute renal failure. The response of the glomerulus to changes in the macula densa stimulus was evaluated in haeme pigment, ischaemic and nephrotoxic induced renal damage by measuring early proximal flow rates. The sodium chloride concentration at the macula densa was varied between low values and isotonicity in two ways: firstly, by interruption of flow through the loop of Henle, followed by orthograde perfusion with Ringers solution; secondly, by retrograde perfusion of the loop of Henle with isosmotic mannitol or Ringers solution. In all nephrons examined, filtration rate was inversely correlated to the macula densa sodium chloride concentration, except during orthograde perfusion with 10−4 M furosemide in Ringers solution, when, despite the high sodium chloride concentration, filtration rate remained high. It is concluded that the mechanism of tubuloglomerular feedback is viable after the onset of compromised renal function, and may, as postulated, account for the reduction in blood flow and nephron filtration rate occurring in acute renal failure.

The early phase of experimental acute renal failure. II. tubular leakage and the reliability of glomerular markers.

SummaryExperiments were designed to determine whether leakage of substances across the tubular epithelium, which are impermeant in the normal kidney, falsifies the measurement of glomerular filtration rate in acute renal failure. Permeability to those substances most commonly used for filtration rate determination, polyfructosan, inulin and ferrocyanide, was estimated by measuring their recoveries following perfusion through various nephron segments in haeme pigment, ischaemic and nephrotoxic models of actue renal failure. Late proximal recovery of14C ferrocyanide was only marginally decreased compared to controls, by a maximum of 6%. Distal recovery of polyfructosan,14C and3H inulin were depressed somewhat more, by a maximum of 11%. Urinary recovery of14C inulin was reduced by only 15% in kidneys showing severely restricted renal function. It is concluded that tubular leakage is not a feature of significance in the early phase of moderate acute renal failure, that ferrocyanide and inulin are reliable markers for the determination of nephron filtration rate and water reabsorption, and that the reduction in whole kidney inulin or polyfructosan clearance reflects primarily a reduction in glomerular filtration rate.

Intracellular elemental concentrations in renal tubular cells. An electron microprobe analysis

SummaryIn order to be able to examine the processes involved in transepithelial transport in tissues, which are not composed of a single cell type, methods are required, which permit analysis at a cellular level. The technique of electron microprobe analysis permits the intracellular concentrations of many elements to be determined simultaneously in various portions of the cell. The application of this method to renal cortical tissue has shown that the best estimates of the cytoplasmic concentrations are to be obtained in regions close to the nucleus, farthest from the basolateral infoldings and microvilli, which separate the intracellular environment from the extracellular space. The nuclear concentrations of Na and K do not differ from those in the surrounding cytoplasm, although those of P and C1 are somewhat higher in cytoplasm. The intracellular element concentrations in the different cell types vary somewhat, proximal tubular cells contain higher concentrations of Na and C1 and lower ones of P than distal tubular cells. Following ischaemia, a manoeuvre know to result in a disturbance of intracellular electrolytes, Na was observed to rise and K to fall only in the non-surface cells of kidneys exposed to the air, but in all cells, if the kidneys were kept air-free in an atmosphere of N2. The proximal and distal tubular cells showed a variable resistance to ischaemia, the distal tubular cells being much more resistant. Despite the severity of the electrolyte disturbance following ischaemia, the intracellular composition was completely restored one hour after re-introducing renal blood flow.

Chapter 8 Quantitative Determination of Electrolyte Concentrations in Epithelial Tissues by Electron Microprobe Analysis

Publisher Summary This chapter describes the methods and data on the intraepithelial electrolyte concentrations in frog skin and rat kidney by electron microprobe analysis (EMA) of thin freeze-dried cryosections. The EMA data obtained from the analysis of transepithelial sodium (Na) transport in frog skin are in good agreement with the chemical analysis of isolated epithelial cells that have been jet-washed in Na-free solution to reduce the amount of extracellular Na. The Na transport compartment comprises all living epithelial layers forming a functional syncytium, where Na enters the epithelium passively across the outer facing membranes of the stratum granulosum, passes via intercellular junctions into deeper epithelial layers, and is actively extruded across the basolateral membranes into the intercellular spaces, from which it diffuses toward the corium. Analyses of electrolyte concentrations in rat kidney tubular cells showed differences in the electrolyte concentrations in proximal and distal kidney tubules in the control that may reflect a functional inhomogeneity in the nephron segments after short-time ischemia—for example, differences in the cellular energy metabolism and/or transport properties of the apical or basolateral cell membranes.