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We have previously shown that the immature tubule is tolerant of prolonged anoxia. In addition, cellular ATP is maintained at 2-fold higher levels during anoxia in the immature tubules compared with the mature tubules. The purpose of this study was: 1) to determine whether anaerobic glycolysis contributes to the tolerance to anoxia and preservation of cellular ATP in immature tubules and 2) to evaluate whether the tolerance demonstrated by immature tubules is dependent on preservation of cellular ATP. Suspensions of proximal tubules from immature (8-10 d) and mature (8-10 wk) rats were subjected to 15 and 45 min of anoxia in a standard buffer and in buffers designed to inhibit glycolysis. Lactate dehydrogenase release was used to assess plasma membrane damage, ATP levels were determined as an index of cellular energy and total lactate production was measured to evaluate glycolytic activity. After 45 min of anoxia, total lactate production was less in immature tubules (101 +/- 48 micrograms of lactate/mg of DNA) compared with mature tubules (148 +/- 36 micrograms of lactate/mg of DNA). After inhibition of glycolytic metabolism, ATP decreased to similar levels in both immature and mature tubules. However, immature tubules remained resistant to anoxic damage (lactate dehydrogenase: mature tubules 38 +/- 4%, immature tubules 29 +/- 1.0%). Therefore, enhanced glycolytic activity does not play a dominant role in the tolerance of the developing kidney to anoxia, and this tolerance is not primarily dependent on preservation of cellular ATP.

Very few data are available regarding the decreased susceptibility of the developing kidney to anoxia. Therefore, the purpose of this study was to develop an experimental system that would allow comparison of an anoxic insult in immature and mature proximal tubule segments and to investigate the hypothesis that the developing kidney is resistant to anoxia as compared with the mature kidney. Suspensions of proximal tubules from immature (age 8-10 d) and mature (8-10 wk) rats were obtained. The purity of the tubule suspension from the immature rats was documented by villin staining. A common buffer solution was developed to compare results from the immature and mature tubules. To study the response of the tubules to anoxia, we subjected the tubule suspension from both the immature and mature rats to 15, 30, 45, and 60 min of anoxia. Lactate dehydrogenase release was measured to assess plasma membrane damage, and ATP levels were determined as an index of cellular energy. After a short anoxic insult (15 or 30 min), the percentage of lactate dehydrogenase release was not significantly different from mature tubules. After prolonged anoxia (45 and 60 min) lactate dehydrogenase release continued to increase, whereas membrane integrity stabilized in the immature tubules. ATP levels decreased in both immature and mature tubules after anoxia, but the decline of ATP was greater in the mature tubules, with a plateau at 20% of basal ATP levels as compared with 40% in the immature tubules. Therefore, the developing kidney is resistant to prolonged anoxia.

Twenty-three patients were evaluated from 1-15 (mean 6) years after recovering from an episode of diarrhea-associated associated childhood hemolytic uremic syndrome (DA-HUS). All patients had received only conservative treatment; none had been given experimental, anti-coagulant, or immunological therapies. Follow-up studies included morphologic and duplex Doppler sonograms. Doppler sonography was used to determine the resistive index, a measure of renovascular resistance. Histories and physical examinations revealed no abnormalities. Results of laboratory studies, which included calculated glomerular filtration rates, were all within normal limits, except for one patient with minor urinary abnormalities. Renal sonograms showed no significant abnormalities of kidney length or parenchymal appearance. However, Doppler sonographic examinations revealed that the DA-HUS patients demonstrated less of a decrease in renovascular resistance with age than did the control group (p < 0.0002). After recovery, patients treated exclusively with conservative management during an acute episode of DA-HUS appeared to have an excellent long-term prognosis. Comparison of our results with those from other studies in which investigational therapies have been used during the acute phase of DA-HUS suggests that latent toxicities which cause long term sequelae may not have been appreciated previously. The clinical significance of the altered renal vascular resistance remains to be delineated.

Previous studies from our laboratory have demonstrated that postischemic infusion of thyroxin (T4) will augment the restoration of cellular ATP and enhance the recovery of renal function. It has not been clear, however, whether T4 has a direct effect on mitochondrial ATP synthesis or an indirect effect by stabilization of the plasma membrane. To differentiate these putative effects, rats were subjected to 45 min of renal ischemia and given either normal saline (0.5 mL) or T4 (20 micrograms/100 g body weight) during the first 15 min of reflow. Cellular ATP levels were assessed by 31P-nuclear magnetic resonance spectroscopy, and release of lactate dehydrogenase (LDH) was used as an index of plasma membrane integrity at 30 and 120 min of reflow. In rats given normal saline, renal ATP had returned to only 57.9 +/- 1.4% of preischemic values at 30 min of reflow and 66.1 +/- 1.4% by 120 min. LDH release was 13 +/- 0.89% at 30 min and 14.6 +/- 1.6% at 120 min. In contrast, T4-treated animals had ATP levels of 70.2 +/- 2.0% at 30 min and 84.0 +/- 1.9% at 120 min, whereas LDH release was elevated to values similar to those in normal saline-treated rats, 14.9 +/- 1.5% and 14.4 +/- 0.5% at 30 min and 120 min, respectively (nonischemic LDH 8.8 +/- 0.8%). These data suggest that T4 stimulates the recovery of renal ATP by a direct effect on synthesis rather than an indirect effect related to global improvement in cellular integrity.

To determine the mode of action of the beneficial effect of adenosine triphosphate (ATP)-MgCl2, recovery of microinjected inulin, proximal tubular pressure (PTP), and cellular damage as quantitated by histomorphometric analysis of necrosis and swelling were evaluated at 2, 6, and 24 hours after 45 minutes of renal ischemia in rats treated with either normal saline or ATP-MgCl2. At 2 hours both groups of rats demonstrated increased permeability to inulin, elevated PTP, and severe ischemic damage and necrosis. By 6 hours ATP-MgCl2 rats had less tubular back leak of inulin, PTP was modestly reduced, and ultrastructural studies demonstrated improved cellular morphologic features with evidence of early regenerative changes. The saline rats had progressive ischemic cellular damage. At 24 hours ATP-MgCl2 rats had reestablished tubular integrity, PtP had fallen, and ischemic alterations were improved, with only focal evidence of necrosis. Saline-treated rats still had a back leak of inulin, elevated PTP, and progressive ischemic injury. This study demonstrates that 1) cellular damage continues to occur for 6 hours after renal ischemia; 2) ATP-MgCl2 enhances recovery of tubular integrity and cellular morphologic features. The salutary effect of ATP-MgCl2 appears related to the preservation of sublethally injured cells and acceleration of the process of restoration and repair of damaged cells.

Children with steroid-dependent frequently relapsing nephrotic syndrome are generally assumed to have a minimal change in histology and therefore to respond favorably to treatment with cyclophosphamide. The clinical course of 38 children with steroid-sensitive frequently relapsing nephrotic syndrome was analyzed. Biopsy samples were obtained from these children several years (mean 6 years) after the onset of their disease but before they were treated with cyclophosphamide. Three histologic types of lesions were found: minimal change lesion, 18 patients (47%); focal and segmental glomerulosclerosis, 11 patients (29%); and mesangial proliferation, 9 patients (24%). Each patient then received cyclophosphamide (2mg/kg of body wt per day) for 12 weeks, and each responded with a complete remission, which lasted 1.5 +/- 0.2 years. During 6 years of followup after cyclophosphamide, 17 patients experienced one or more relapses, but 21 patients remained in sustained remission. The incidence of relapse after cyclophosphamide was significantly greater (P less than 0.01) in the patients with focal and segmental glomerulosclerosis (8/11, 73%) and mesangial proliferation (5/9, 56%), as compared with children with minimal change lesion (4/18, 22%). These data indicate that children with frequently relapsing steroid-dependent nephrotic syndrome (1) will not all develop minimal-change lesions within several years; in fact, approximately half will have either focal and segmental glomerulosclerosis or mesangial proliferation; and (2) after cyclophosphamide treatment, the incidence of relapse will be related to the histopathologic type of lesion present at the time of treatment with cyclophosphamide.

Renal energy metabolism was investigated before, during, and after ischemic insults of varying durations with in vivo 31P NMR spectroscopy. The postischemic recovery of renal ATP was found to be a biphasic process regardless of the length of the ischemia. This two-stage recovery consisted of a quick initial component immediately upon reflow followed by a slower, more gradual return toward preischemic levels. To characterize the source of each phase of the recovery, kidneys were extracted with perchloric acid at the end of the different periods of ischemia (before reflow). Concentrations of adenine nucleotides and breakdown products adenosine, inosine, and hypoxanthine were determined by 1H NMR spectroscopy. Excellent correlation was found between the residual nucleotide pool and the magnitude of the initial phase of ATP recovery. Additionally, the renal ATP content after 120 min of reflow was shown to have a strong correlation with subsequent functional recovery. These experiments show that in vivo 31P NMR can provide new and dynamic information concerning the biochemical recovery from ischemia. Furthermore, this data has the potential to predict the eventual functional recovery of the organ.

This study was designed to investigate the effects of ATP-MgCl2 when infused immediately 8 or 24 hr after 45 min of bilateral renal artery ischemia and to determine if an initial improvement in clearance of inulin (CIn) would be sustained throughout the course of recovery. In addition, the influence of ATP-MgCl2 on the pattern of recovery of whole kidney and single nephron function was assessed by determining the impact of this agent on proximal tubular pressure and transepithelial backleak. The postischemic administration of ATP-MgCl2 resulted in significantly enhanced recovery of CIn irrespective of the time of the infusion after the initial insult. This beneficial effect was sustained in that the ATP-MgCl2-treated rats had significantly better CIn 1, 3 and 7 days after the injury when compared to normal saline-treated animals. Moreover, single nephron inulin clearance (SNCIn) was better preserved than whole kidney CIn in both groups of animals and in the ATP-MgCl2-treated animals SNCIn was similar to control values even 1 day after the injury. The enhanced recovery of single nephron function in the ATP-MgCl2-treated animals resulted from reduced proximal tubular pressure and diminished backleak of tubular fluid. Animals given ATP-MgCl2 had better preservation of cellular morphology. Horseradish peroxidase was excluded from most epithelial cells and the interstitium in a manner similar to that seen in control animals while saline-treated rats demonstrated backleak of this tracer compound. Based on these studies, it appears that the beneficial effect of ATP-MgCl2 occurs because of the preservation of sublethally injured cells by augmentation of the process of recovery.

To determine the effect of thyroxin (T4) on the recovery from toxic acute renal failure, rats were injected, subcutaneously, with K-dichromate (15 mg/kg) and at the peak of the renal injury, each animal was given either T4 (4 micrograms/100 g body weight, i.p.) or normal saline (NS). The T4-treated rats had significantly better CIn (669 +/- 35 microliter/min/100 g body weight), improved FENa (0.49 +/- 0.05%) and increased UOsm (835 +/- 50 mOsm/kg) as compared to animals given only NS (CIn 422 +/- 27; FENa 1.02 +/- 0.12; and UOsm 613 +/- 23). A similar dose of T4 given to non-injured control rats had no effect on renal function. The beneficial effect of T4 on dichromate injected rats was sustained and lead to more prompt recovery of glomerular function. To eliminate any hemodynamic effects of T4, an isolated perfused kidney preparation was utilized, and kidneys from dichromate injected rats treated with T4 had significantly better CIn, urine flow and FENa compared to rats given NS. Cellular morphology was better preserved in T4-treated animals. These data indicate that treatment with T4 results in enhanced recovery from an acute toxic renal insult and that this beneficial effect is unlikely to be related to nonspecific systemic effects of the hormone.

The concentrations of renal ATP have been measured by 31P-nuclear magnetic resonance (NMR) before, during, and after bilateral renal artery occlusion. Using in vivo NMR, the initial postischemic recovery of ATP increased with the magnitude of the residual nucleotide pool at the end of ischemia. ATP levels after 120 min of reflow correlated with functional recovery at 24 h. In the present study the effect of blocking the degradation of ATP during ischemia upon the postischemic restoration of ATP was investigated. Inhibition of adenosine deaminase by 80% with the tight-binding inhibitor 2'-deoxycoformycin led to a 20% increase in the residual adenine nucleotide pool. This increased the ATP initial recovery after 45 min of ischemia from 52% (in controls) to 62% (in the treated animals), as compared to the basal levels. The inhibition also caused an accelerated postischemic restoration of cellular ATP so that at 120 min it was 83% in treated rats vs. 63% in untreated animals. There was a corresponding improvement in the functional recovery from the insult (increase of 33% in inulin clearance 24 h after the injury). Inhibition of adenosine deaminase during ischemia results in a injury similar to that seen after a shorter period of insult.

Although a number of manipulations prior to or during the initiation phase of an acute renal injury will modify the degree of functional impairment, agents administered after the acute insult usually have been ineffective. In the present study, adenine nucleotides (AMP, ADP, or ATP) combined with magnesium chloride were infused after an ischemic renal injury. Twenty-four hours later: (1) rats that received no infusion or one of the components of the mixture alone had reduced CIn (355 +/- 40 microliter/min/100 g of body wt vs. 977 +/- 40 control value), decreased RBF (3550 +/- 205 microliter/min/100 g of body wt vs. 5095 +/- 171 control value), elevated FENa (0.65 +/- 0.10% vs. 0.17 +/- 0.04 control value), and diminished UOsm (862 +/- 110 mOsm/kg vs. 1425 +/- 132 control value); (2) rats given dopamine or phenoxybenzamine maintained low CIn (365 +/- 50) despite improved RBF (4678 +/- 222); (3) rats infused with either AMP, ADP, or ATP combined with magnesium chloride had markedly improved CIn (594 +/- 44, P < 0.01), increased RBF (4269 +/- 223, P < 0.01); normalized FENa (0.18 +/- 0.07%, P < 0.01), and improved UOsm (1201 +/- 106 mOsm/kg, P < 0.05). In animals given no infusion or only magnesium chloride, ultrastructural studies demonstrated focal cellular necrosis and marked generalized tubular cell and mitochondrial swelling, whereas rats infused with ATP and magnesium chloride had fewer ultrastructural changes with better preservation of cellular morphology. Rats treated with ATP and magnesium chloride had improved CIn despite ischemic periods of 30, 45, and 60- min; and the degree of improvement was directly related to the quantity of ATP and magnesium chloride administered. The cellular content of exogenously administered ATP was 2.5 times greater in previously ischemic kidneys than in nonischemic kidneys. The data indicate that adenine nucleotides combined with magnesium chloride when infused after the initiation of acute renal failure significantly improve both CIn and tubular function and suggest that these agents effectively enhance recovery following an ischemc renal insult.

This article will provide a pathophysiologic basis for the assessment of critically ill children who have developed disorders of urine volume. The anatomical and pathophysiologic causes of oliguria and polyuria are considered. The physiologic basis for the use of urinary sodium and osmolarity as a guide to the assessment of patients with disorders of urine volume are discussed in detail. In addition, guidelines for the management of children with acute renal failure, with particular emphasis on the consideration for nutritional support of these patients, is discussed as a part of the comprehensive approach to this problem. This article emphasizes an understanding of the pathophysiology of salt and water excretion by the kidney as a foundation to the diagnosis and management of patients with oliguria and polyuria.