PLASMA RENIN ACTIVITY IN ACUTE TUBULAR NECROSIS AND OTHER RENAL DISEASES ASSOCIATED WITH HYPERTENSION

The influence of extracellular and intracellular calcium on the secretion of renin

Changes in plasma, extracellular, and intracellular calcium can affect renin secretion from the renal juxtaglomerular (JG) cells. Elevated intracellular calcium directly inhibits renin release from JG cells by decreasing the dominant second messenger intracellular cyclic adenosine monophosphate (cAMP) via actions on calcium-inhibitable adenylyl cyclases and calcium-activated phosphodiesterases. Increased extracellular calcium also directly inhibits renin release by stimulating the calcium-sensing receptor (CaSR) on JG cells, resulting in parallel changes in the intracellular environment and decreasing intracellular cAMP. In vivo, acutely elevated plasma calcium inhibits plasma renin activity (PRA) via parathyroid hormone-mediated elevations in renal cortical interstitial calcium that stimulate the JG cell CaSR. However, chronically elevated plasma calcium or CaSR activation may actually stimulate PRA. This elevation in PRA may be a compensatory mechanism resulting from calcium-mediated polyuria. Thus, changing the extracellular calcium in vitro or in vivo results in inversely related acute changes in cAMP, and therefore renin release, but chronic changes in calcium may result in more complex interactions dependent upon the duration of changes and the integration of the body's response to these changes.

Hypercalcemia reduces plasma renin via parathyroid hormone, renal interstitial calcium, and the calcium-sensing receptor

Acute hypercalcemia inhibits plasma renin activity (PRA). How this occurs is unknown. We hypothesized that acute hypercalcemia inhibits PRA via the calcium-sensing receptor because of parathyroid hormone-mediated increases in renal cortical interstitial calcium via TRPV5. To test our hypothesis, acute in vivo protocols were run in sodium-restricted, anesthetized rats. TRPV5 messenger RNA expression was measured with real-time quantitative RT-PCR. Acute hypercalcemia significantly decreased PRA by 37% from 32.0±3.3 to 20.3±2.6 ng of angiotensin I per milliliter per hour (P<0.001). Acute hypercalcemia also significantly increased renal cortical interstitial calcium by 38% (1.73±0.06 mmol/L) compared with control values (1.25±0.05 mmol/L; P<0.001). PRA did not decrease in hypercalcemia in the presence of a calcium-sensing receptor antagonist, Ronacaleret (22.8±4.3 versus 21.6±3.6 ng of angiotensin I per milliliter per hour). Increasing plasma calcium did not decrease PRA in parathyroidectomized rats (22.5±2.6 versus 22.0±3.0 ng of angiotensin I per milliliter per hour). Parathyroidectomized rats were unable to increase their renal cortical interstitial calcium in response to hypercalcemia (1.01±0.11 mmol/L). Acutely replacing plasma parathyroid hormone levels did not modify the hypercalcemic inhibition of PRA in parathyroid-intact rats (39.1±10.9 versus 16.3±3.2 ng of angiotensin I per milliliter per hour; P<0.05). Renal cortical TRPV5 messenger RNA expression decreased by 67% in parathyroidectomized (P<0.001) compared with intact rats. Our data suggest that acute hypercalcemia inhibits PRA via the calcium-sensing receptor because of parathyroid hormone-mediated increases in renal cortical interstitial calcium via TRPV5.

Protection of canine renal grafts by renin-angiotensin inhibition through nucleoside transport blockade

The aims of this study were (1) to investigate the effect of R 75231, a nucleoside transport inhibitor, on renin-angiotensin release after renal ischemia-reperfusion and (2) to establish a possible protective effect of this drug on renal function. We used a canine model for auto- transplantation of kidneys that had been subjected to 30 min of warm ischemia and subsequently to 24h of cold storage in HTK preservation solution, with immediate contralateral nephrectomy. R 75231 was injected intravenously into six dogs in two equal portions of 0.05 mg/kg both 30 min and 10 min before reanastomosis was established. Another six dogs were used as a control group. At 2 weeks post-transplantation, five out of six dogs in the R 75231 group and one out of six in the control group were still alive. Starting on day 4, serum creatinine was lower in the R 75231 group than in the control group (p < 0.005). In contrast to the control group, an inversion of the median preischemia adenosine/inosine ratio was observed in the R 75231 group after reperfusion (0.4 preischemia vs 4.0 after 60 min of reperfusion). Reperfusion of the graft resulted in an immediate increase in renin, angiotensin I, and angiotensin II venous blood levels in the control group. In the R 75231 group, renin, angiotension I, and angiotensin II levels were significantly lower. We conclude that administration of R 75231 before reperfusion has a protective effect on post-transplant function of kidneys that have been subjected to prolonged warm ischemia. This effect may, at least in part, be ascribed to inhibition of the breakdown and disposal of endogenous adenosine which, in turn, inhibits the excessive stimulation of the renin-angiotensin system in the early phase of reperfusion.

[Change in renin activity and blood pressure in the dog autologous kidney transplant model with modified HTK solution]

Investigations of changes in activity of renin and blood pressure after reperfusion of the kidney transplant using HTK solution were carried out by means of an autologous, heterotopic model of kidney transplantation applied to dogs. Duration of cold ischemia was 48 h. According to variations in the composition of the HTK perfusion solution three test groups were set up. During the first 20 min after recirculation in each test group the renal venous and arterial renin activities were measured. Parallel to renin activity, the arterial blood pressure was recorded. During the first few minutes following recirculation of the kidney transplant the renin levels in the venous blood of the kidney were higher in test group 1 (HTK solution, perfusion height 120 cm) than in either of the other two, showing a median maximal increase of 195 ng/ml.h. In test group 2 the maximal venous renin concentration fell to 145 ng/ml.h, while graphs take a more uniform course. Test group 3 (HTK/tryptophan) differed from the others in having further improved renin values. After the 7.5 min of observation normal venous renin concentrations were measured following earlier values for maximal increase between 23.1 ng/ml.h and 120 ng/ml.h (median 61.5 ng/ml.h). The best reperfusion of the kidney was observed in the tryptophan group, albeit without any recognizable positive effects on the other renal functions. Initially low renin values do not necessarily correlate with a smooth postoperative renal function and vice versa. Initial renin values cannot provide a secure basis for predicting instant as well as long-term postoperative functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of filtration failure during postischemic injury of the human kidney. A study of the reperfused renal allograft

Postischemic filtration failure in experimental animals results primarily from depression of the transcapillary hydraulic pressure difference (delta P), a quantity that cannot be determined in humans. To circumvent this limitation we determined the GFR and each of its remaining determinants in transplanted kidneys. Findings in 12 allografts that exhibited subsequent normofiltration (group 1) were compared with those in 11 allografts that exhibited persistent hypofiltration (group 2). Determinations were made intraoperatively in the exposed graft after 1-3 h of reperfusion. GFR (6 +/- 2 vs 29 +/- 5 ml/min) and renal plasma flow by Doppler flow meter (140 +/- 30 vs 315 +/- 49 ml/min) were significantly lower in group 2 than group 1. Morphometric analysis of glomeruli obtained by biopsy and a structural hydrodynamic model of viscous flow revealed the glomerular ultrafiltration coefficient to be similar, averaging 3.5 +/- 0.6 and 3.1 +/- 0.2 ml/(min.mmHg) in group 2 vs 1, respectively. Corresponding values for plasma oncotic pressure were also similar, averaging 19 +/- 1 vs 21 +/- 1 mmHg. We next used a mathematical model of glomerular ultrafiltration and a sensitivity analysis to calculate the prevailing range for delta P from the foregoing measured quantities. This revealed delta P to vary from only 20-21 mmHg in group 2 vs 34-45 mmHg in group 1 (P < 0.001). Further morphometric analysis revealed the diameters of Bowman's space and tubular lumens, as well as the percentage of tubular cells that were necrotic or devoid of brush border, to be similar in the two groups. We thus conclude (a) that delta P depression is the predominant cause of hypofiltration in this form of postischemic injury; and (b) that afferent vasoconstriction rather than tubular obstruction is the proximate cause of the delta P depression.

Reduced Na-K-ATPase in distal nephron in glycerol-induced acute tubular necrosis

To further characterize changes in tubular Na-K-ATPase in acute tubular necrosis (ATN), segmental analysis was performed in rat nephrons. Na-K-ATPase was assayed in the following segments: proximal convolution (PC), proximal straight (PS), outer medullary thick ascending limb (MTAL), cortical thick ascending limb (CTAL), distal convolution (DC) and cortical collecting duct (CCD) in three groups of rats: 1.) intact; 2.) moderate non-oliguric ATN; and 3.) severe oliguric ATN. GFR and CNa/GFR X 100 were in group 1 0.80 +/- 0.05 ml/min and 0.68 +/- 0.06, in group 2 0.14 +/- 0.02 and 1.46 +/- 0.35, and in group 3 0.04 +/- 0.01 and 0.46 +/- 0.15, respectively. Na-K-ATPase in PC and PS were similar in all three groups. Na-K-ATPase levels were in MTAL: in group 1 37 +/- 2 X 10(-11) mol/mm/min, in group 2 20 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 24 +/- 2 X 10(-11), P less than 0.001 versus group 1. In CTAL Na-K-ATPase levels were: in group 1 40 +/- 2 X 10(-11), in group 2 33 +/- 1 X 10(-11), P less than 0.001 versus group 1, and in group 3 27 +/- 2 X 10(-11), P less than 0.001 versus groups 1 and 2.(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of protracted acute renal failure in man

Postischemic acute renal failure (ARF) induced by cardiac surgery is commonly prolonged and may be irreversible. To examine whether persistence of postischemic, tubular cell injury accounts for delayed recovery from ARF, we studied 10 patients developing protracted (36 +/- 4 d) ARF after cardiac surgery. The differential clearance and excretion dynamics of probe solutes of graded size were determined. Inulin clearance was depressed (5.0 +/- 1.7 ml/min), while the fractional urinary clearance of dextrans (radii 17-30 A) were elevated above unity. Employing a model of conservation of mass, we calculated that 44% of filtered inulin was lost via transtubular backleak. The clearance and fractional backleak of technetium-labeled DTPA ([99mTc]DTPA, radius = 4 A) were identical to those of inulin (radius 15 A). The time at which inulin or DTPA excretion reached a maximum after an intravenous bolus injection was markedly delayed when compared with control subjects with ARF of brief duration, 102 vs. 11 min. Applying a three-compartment model of inulin/DTPA kinetics (which takes backleak into account) revealed the residence time of intravenously administered inulin/DTPA in the compartment occupied by tubular fluid and urine to be markedly prolonged, 20 vs. 6 min in controls, suggesting reduced velocity of tubular fluid flow. We conclude that protracted human ARF is characterized by transtubular backleak of glomerular ultrafiltrate, such that inulin clearance underestimates true glomerular filtration rate by approximately 50%, and by sluggish tubular fluid flow, which strongly suggests the existence of severe and generalized intraluminal tubular obstruction. Because all patients also exhibited extreme hyperreninemia (16 +/- 2 ng/ml per h) that was inversely related to inulin clearance (r value = -0.83) and urine flow (r value = -0.70), we propose that persistent, angiotensin II-mediated renal vasoconstriction may have delayed healing of the injured tubular epithelium.

Renal and systemic hemodynamics in sustained essential hypertension

Cardiac output (CO), renal blood flow (RBF), calf blood flow (CBF), and hepatic blood flow (HBF), glomerular filtration rate (GFR), and dopamine beta hydroxylase (D beta H) activity were studied in 198 men (67 normotensive controls and 131 hypertensive patients) of the same age with sustained uncomplicated essential hypertension. In the hypertensive men, the RBF and the RBF/CO ratio were significantly decreased (p less than 0.001). The RBF and RBF/CO ratio were negatively correlated with age (p less than 0.01), blood pressure (p less than 0.01), and D beta H activity (p less than 0.01). None of these relationships were observed with CBF and HBF. The observed decreases in RBF and the RBF/CO ratio in hypertensive men were reversed after administration of clonidine and alpha-methyldopa (p less than 0.01), but not after administration of propranolol. The study provides evidence that the reduction of renal perfusion in essential hypertension is partly reversible and related to an abnormality in the adrenergic system control.

Myoglobinuric renal failure due to drug-induced rhabdomyolysis

1 Two cases of drug-induced rhabdomyolysis, one of them presenting with acute myoglobinuric renal failure are described. 2 The pathogenesis of rhabdomyolysis and renal failure in our cases is discussed with reference to work published by other authors. 3 Whereas there seems to be obvious evidence for direct toxic drug-muscle interaction, the mechanism for the development of myoglobinuric renal failure remains unclear.

The sympathetic nervous system in the pathogenesis of acute renal failure

The purpose of this review is to highlight the participation and the possible role of the renal sympathetic nervous system in the development of renal cell damage and the consequent dysfunctions and filtration filtration failure.

Attenuation of nephrotoxic acute renal failure in the dog with angiotensin-converting enzyme inhibitor (SQ-20,881)

Angiotensin-converting enzyme inhibitor was used in dogs with uranyl nitrate-induced acute renal failure to evaluate (1) a possible protective effect of angiotensin blockade and (2)the role of angiotensin II in the generation of renal failure in this model. Angiotensin-converting enzyme inhibitor treatment attenuated the fall in glomerular filtration rate and renal blood flow during the first 6 hours after injection of the nephrotoxic agent. A protective effect of similar magnitude was observed whether angiotensin-converting enzyme inhibitor treatment preceded, or shortly followed, the administration of uranyl nitrate. This indicates that angiotensin-converting enzyme inhibitor delivery to its intrarenal site of action remains effective after administration of the nephrotoxin. In addition, protection of glomerular filtration rate correlated with sodium and renal solute excretion. However, combined treatment with angiotensin-converting enzyme inhibitor and furosemide enhanced solute excretion but did not further improve the protection of renal function. Finally, the protective effects of angiotensin-converting enzyme inhibitor on renal function and hemodynamics were abolished by intravenous indomethacin. In conclusion, early, continuous blockade of angiotensin II protects partially against th initiation of acute renal failure. These findings support a major pathogenic role for angiotensin II in the generation phase of acute renal failure in this model. Furthermore, they suggest that an imbalance between vasoconstrictive (angiotensin II) and vasodilating factors (prostaglandins) may be operative in the early phase of uranyl nitrate-induced acute renal failure in the dog.

Norepinephrine-induced acute renal failure: a reversible ischemic model of acute renal failure

The present study has defined conditions whereby a reversible form of ischemia-induced ARF can be produced in the dog. Unlike previous studies [9-11] which examined the acute phase of NE-induced ARF, this study demonstrates the feasibility of using the model for the longitudinal study of ARF. Such a model may be useful in studying the pathologic and physiologic changes which occur during different phases of ARF. Perhaps most important, this model should also provide a setting in which treatment measures, either prophylactic or therapeutic for ARF, can be examined.

Action of the competitive angiotensin II antagonist saralasin during the initial phase of glycerol-induced acute renal failure of the rat

The effects of the competitive angiotensin II antagonist saralasin (1-sarcosine-8-alanine-5-isoleucine-angiotensin II) on renal function in healthy rats and in rats with myohemoglobinuric acute renal failure were studied. Acute renal failure was induced by an intramuscular injection of 50% glycerol (10 ml.kg-1). Functional impairment of the glycerol treated animals consisted in a decrease of renal blood flow (electromagnetic flowmeter) and GFR and in an increase of urine volume and arterial blood pressure. In healthy rats saralasin (6 microgram.kg-1.min-1 i.v.) had no renal effects by itself but antagonized the angiotensin II (200 ng.kg-1.min i.v.) induced fall of renal blood flow and GFR and the increase of arterial blood pressure. Given to glycerol treated animals saralasin did not induce any change of arterial blood pressure, renal blood flow, GFR or the urinary excretion of fluid and sodium.

Plasma renin and angiotensin II in acute renal failure

The role of raised plasma renin and angiotensin-II concentrations in the development of acute renal failure in man was examined in patients in shock from various causes and in patients in whom hypotension was used to promote haemostasis. Ten of the thirteen patients in shock had raised angiotensin-II concentrations in peripheral blood and acute renal failure manifested by oliguria, increasing serum-creatinine, a urine osmolality of less than 400 mos-mol/kg and a urine/plasma osmolality ratio of less than 1-5. Although patients who were hypotensive for periods of 1 h 45 min to 4 h to promote haemostasis during surgery had similarly raised plasma-renin activity and angiotensin-II concentrations in peripheral venous blood, they did not have acute renal failure. It is concluded that high plasma-angiotensin-II concentrations do not explain the pathogenesis of acute renal failure in patients in shock.

Reduction in severity of acute renal failure in rats by beta-adrenergic blockade

The effectiveness of beta-adrenergic blockade in preventing acute renal failure (A.R.F.) in rats was studied in the hypoxia model produced by unilateral nephrectomy and clamping of the contralateral renal artery for 70 minutes. Beta-adrenergic blockade effectively reduced the severity of A.R.F. in this experimental model. Treatment with a combination of propranolol and a synthetic angiotensin-II competitive inhibitor (P113) produced no further improvement. These results are consistent with the view that intrarenal release of renin is to some extent involved in the pathogenesis of A.R.F.

Reaction constants of renin in juxtaglomerular apparatus and plasma renin activity after renal ischemia and hemorrhage

Reaction constants of renin in juxtaglomerular apparatus and plasma renin activity after renal ischemia and hemorrhage. During and after total renal ischemia and acute hemorrhage, renin activity in plasma (PRA) and microdissected juxtaglomerular apparatus (JGA) of rabbits were investigated. In controls, the apparent Michaelis-Mentoen constant (MMC) of semipurified standard renin of rabbits was 1025 plus or minus 223 SD ng/ml. Plasma renin of normal rabbits showed similar values: 1062 plus or minus 138 SD ng/ml. Intrarenal JGA renin, however, showed a great scatter of MMC (920 to 4760 ng/ml) and a significantly higher mean value of 2572 plus or minus 1156 SD ng/ml (pis less than 0.001). After complete renal ischemia by clamping both renal arteries for a 90-min period, the following results wereobtained: 1) Sixty min after the beginning of ischemia, PRA decreased from 20.9 plus or minus 9.8 SD to 7.6 plus or minus 5.2 SD ng/ml-hr (P is less than 0.05) and increased to 103, 68 and 42 ng/ml-hr 10, 30 and 90 min after removal of the clamps, respectively (P is less than 0.05).

Active and passive immunization to angiotensin in experimental acute renal failure

A number of studies support, and others fail to support, the concept that the renin-angiotensin system plays a key role in the pathogenesis of acute renal failure. This study, employing active and passive immunization against angiotensin II, was designed to examine the primacy of circulating angiotensin as a mediator of this syndrome. Neither mode of immunization significantly affected the degree of azotemia or the marked reduction of inulin clearance expected in rats subjected to glycerol-induced myohemoglobinuria. Twenty-four hours after challenge, inulin clearance (Cin) in actively immunized rats fell to 3.2% of control and that of unimmunized rats given the same dose of glycerol was 2.5% of control. Although there was some variation among groups of passively immunized rats, Cin of one group being 18% of control, Cin of the other groups was less than 3% of control. The dose and binding capacity of the immune globulin used here were essentially the same as those reported in another study in which immunization was thought to be of prophylactic value in rats subjected to s.c. administered glycerol injections. Technologic differences unrelated to immunization are suggested to have caused the difference in results in the two studies, and it seems doubtful that circulating angiotensin plays a key role in the pathogenesis of myohemoglobinuric acute renal failure in the rat.

Plasma renin activity in acute poststreptococcal glomerulonephritis and the haemolytic-uraemic syndrome

Plasma renin activity (PRA) was determined in 10 children with acute glomerulonephritis and in 10 with the haemolytic-uraemic syndrome (HUS). Low renin levels were found in the hypertensive children with acute nephritis, all of whom had evidence of fluid overload. The amount of this overload correlated directly with the degree of hypertension and inversely with PRA. All the hypertensive children with HUS had high levels of plasma renin, and the highest levels were found in those cases who were subsequently shown to have the more severe degree of renal arteriolar occlusion. The findings emphasize the importance of measures designed to reduce salt and water overloading in the management of hypertension in acute nephritis, while drugs which suppress plasma renin are more likely to control blood pressure in HUS. Estimation of PRA may provide a guide to the management of hypertension in acute renal insufficiency.

Experimental acute renal failure induced by uranyl nitrate in the dog

The diminished glomerular filtration rate observed in previous studies of acute renal failure induced by uranyl nitrate has been ascribed to backflow of glomerular filtrate through necrotic tubular epithelium, since renal blood flow was essentially normal. Renal blood flow ( 133 xenon washout) and renal function were studied serially for 96 hours after the administration of uranyl nitrate (10 mg/kg, iv) in unanesthetized dogs with chronic renal artery catheters. Inulin clearance and total renal blood flow decreased to 25% and 52% of control, respectively, by 6 hours and remained depressed. By 3 hours, cortical flow decreased to 330±20 ml/min 100 g -1 (control 507±12 ml/min 100 g -1 ) and outer medullary flow increased to 147±8 ml/min 100 g -1 (control 97±18 ml/min 100 g -1 ), indicating intrarenal blood flow redistribution. From 6 hours on, these flow components were no longer separable. The ratio of flow in the outer two-thirds of the renal cortex to that in the whole cortex, determined using 85 strontium-labeled microspheres (15µ), decreased to 0.34±0.06 and 0.40±0.04 at 6 and 96 hours, respectively (control 2.21±0.12). Plasma renin activity was 1.8±0.6 ng/ml hour -1 at 3 hours and remained elevated (control 0.6±0.2 ng/ml hour -1 ). Histological examination revealed minimal tubular change at 6 hours and widespread disruption at 96 hours. The decrease in renal blood flow prior to any significant tubular pathology suggests that alterations in renal hemodynamics, which may be mediated by the renin-angiotensin system, are responsible for the diminished renal function observed in this model of acute renal failure.

Management of acute renal failure

Acute renal failure has oliguria and uraemia as its cardinal manifestations. The syndrome may be due to acute tubular necrosis, glomerulonephritis, urinary tract obstruction and occlusive vascular disease.

The renal damage due to acute tubular necrosis is of uncertain aetiology. Renal cortical ischaemia and depression of glomerular filtration rate are important in the pathogenesis. Activation of the renin-angiotensin system and glomerular coagulation may prove to be important in these changes.

The differentiation between reversible oliguria and established renal failure is generally accomplished on clinical grounds and the response to a therapeutic trial of mannitol. Measurement of urinary sodium concentration and osmolality are valuable adjuncts.

The keystone of management is the prevention of symptomatic uraemia. Infection and haemorrhage have now replaced pulmonary oedema and hyperkalaemia as the major causes of death. The mortality rate remains high in acute tubular necrosis and a significant mortality occurs in the diuretic phase.

Renin and acute circulatory renal failure in the rabbit

Plasma renin concentration (PRC) was measured in 25 rabbits before and 6, 24, or 72 hours after subcutaneous injection of glycerol. Renal failure and tubular necrosis developed in most animals and PRC rose sixfold to a maximum at 24 hours. Small insignificant changes of PRC were present at 6 and 72 hours. None of these changes was observed in a control group of nine animals killed 24 hours after an injection of saline. The amount of renin extractable from single superficial glomeruli and from renal cortical tissue was reduced after injection of glycerol. In a second study of 11 anesthetized rabbits, renal venous PRC increased on average from 151 to 1810 units/liter following a 4-hour period of renal artery occlusion. Arterial PRC did not change significantly during this time, but the kidneys showed histological changes of acute tubular necrosis. These experiments are compatible with the suggestion that renin is involved in the pathogenesis of acute circulatory renal failure.

Micropuncture studies of the recovery phase of myohemoglobinuric acute renal failure in the rat

Micropuncture studies of the recovery phase of glycerol-induced myohemoglobinuric acute renal failure were performed in rats whose blood urea nitrogen (BUN) had fallen at least 20% below its peak value. The glomerular filtration rate (GFR) of individual nephrons in a single kidney in the recovery period generally either was in the normal range or minimal. Each animal's BUN concentration at the time of the study was inversely related to the proportion of functioning surface nephrons, but did not correlate with individual nephron GFR values. Proximal tubule fractional water absorption was significantly depressed as manifested by both depressed inulin (TF/P) values and supernormal volumes of collections, a finding which, in the absence of a urea-induced osmotic diuresis, suggests impaired sodium transport by the damaged nephron. The mean proximal tubule hydrostatic pressure in recovery was normal and there was little variation in pressure among functioning nephrons. It is concluded that recovery from this model of acute renal failure reflects the progressive recruitment of increasing numbers of functioning nephrons. The recovery of individual nephron glomerular filtration, once begun, was rapid and complete. No evidence could be adduced that the gradual return of renal function towards normal reflects a slow release of tubular obstruction or repair of disrupted tubular epithelium. Rather, recovery appeared to be directly attributable to the return of an adequate effective glomerular filtration pressure. Significant limitation in proximal tubule water absorption persisted after individual nephron GFR had returned to normal or supernormal values in this model of experimental acute renal failure in the rat, a finding which readily accounts for the diuresis associated with the recovery phase of this syndrome.

Renin and acute renal failure: studies in man

Plasma renin concentration was increased, usually appreciably, in 22 out of 25 patients with acute renal failure, the average value being 226 units/litre (mean for normal subjects 8.2 units/1.). The highest renin values were found in the first 10 days of the disease; lower and sometimes normal values were found subsequently. Unequivocal acute tubular necrosis was present in only two of the eight cases examined post mortem.These findings are compatible with Goormaghtigh's proposal that an excess of renin and angiotensin may act within the kidney to produce acute renal failure.

Plasma renin activity in end-stage kidney disease

Plasma renin activity, fluid and electrolyte balance, and hemodynamic conditions were measured in seven hypertensive patients with end-stage renal disease before and after five exchanges of peritoneal dialytic fluids which removed large amounts of water and sodium, sodium but little water, and little water and sodium, respectively. The subjects had normal plasma renin activity, severe anemia, high cardiac output, high total peripheral resistance, and elevated blood volume. Plasma renin activity rose with large losses of sodium and water but changed slightly when large amounts of sodium with little water or small amounts of sodium and water were removed. Plasma renin activity prior to dialysis did not correlate with mean arterial pressure, blood volume, cardiac index, total peripheral resistance, or serum sodium concentration. Change in plasma renin activity with dialysis correlated inversely with change in mean arterial pressure, water balance, and change in cardiac output, and directly with change in total peripheral resistance and change in serum sodium concentration. There was no correlation with change in blood volume or sodium balance.