Elevation of intrarenal adenosine by maleic acid decreases GFR and renin release

Evaluating renin and aldosterone levels in children with organic acidemia-therapeutic experience with fludrocortisone

Hyporeninemic hypoaldosteronism has been reported in only a few cases with methylmalonic acidemia (MMA) and has been attributed to the renal involvement. This study aims to investigate renin-aldosterone levels along with the renal functions of the patients with organic acidemia. This is a cross-sectional study conducted in patients with MMA, propionic acidemia (PA), and isovaleric acidemia (IVA). Serum renin, aldosterone, sodium, and potassium levels were measured, and glomerular filtration rates (GFR) were calculated. Comparisons were made between the MMA and non-MMA (PA+IVA) groups. Thirty-two patients (MMA:PA:IVA = 14:13:5) were included. The median GFR was significantly lower in the MMA group than in the non-MMA group (p < 0.001). MMA patients had the highest incidence of kidney damage (71.4%), followed by PA patients (23%), while none of the IVA patients had reduced GFR. GFR positively correlated with renin levels (p = 0.015, r = 0.433). Although renin levels were significantly lower in the MMA group than the non-MMA group (p = 0.026), no significant difference in aldosterone levels was found between the two groups. Hyporeninemic hypoaldosteronism was found in 3 patients with MMA who had different stages of kidney damage, and fludrocortisone was initiated, which normalized serum sodium and potassium levels.  Conclusions: This study, which has the largest number of patients among the studies investigating the renin-angiotensin system in organic acidemias to date, has demonstrated that hyporeninemic hypoaldosteronism is not a rare entity in the etiology of hyperkalemia in patients with MMA, and the use of fludrocortisone is an effective treatment of choice in selected cases. What is Known: • Hyperkalemia may be observed in cases of methylmalonic acidemia due to renal involvement and can be particularly prominent during metabolic decompensation. • Hyporeninemic hypoaldosteronism has been reported to be associated with hyperkalemia in only a few cases of methylmalonic acidemia. What is New: • Hyporeninemic hypoaldosteronism was found in one-fifth of cases with methylmalonic acidemia. • Fludrocortisone therapy leads to the normalization of serum sodium and potassium levels.

Extracellular Nucleotides and P2 Receptors in Renal Function

The understanding of the nucleotide/P2 receptor system in the regulation of renal hemodynamics and transport function has grown exponentially over the last 20 yr. This review attempts to integrate the available data while also identifying areas of missing information. First, the determinants of nucleotide concentrations in the interstitial and tubular fluids of the kidney are described, including mechanisms of cellular release of nucleotides and their extracellular breakdown. Then the renal cell membrane expression of P2X and P2Y receptors is discussed in the context of their effects on renal vascular and tubular functions. Attention is paid to effects on the cortical vasculature and intraglomerular structures, autoregulation of renal blood flow, tubuloglomerular feedback, and the control of medullary blood flow. The role of the nucleotide/P2 receptor system in the autocrine/paracrine regulation of sodium and fluid transport in the tubular and collecting duct system is outlined together with its role in integrative sodium and fluid homeostasis and blood pressure control. The final section summarizes the rapidly growing evidence indicating a prominent role of the extracellular nucleotide/P2 receptor system in the pathophysiology of the kidney and aims to identify potential therapeutic opportunities, including hypertension, lithium-induced nephropathy, polycystic kidney disease, and kidney inflammation. We are only beginning to unravel the distinct physiological and pathophysiological influences of the extracellular nucleotide/P2 receptor system and the associated therapeutic perspectives.

The efficacy of theophylline in preventing cisplatin-related nephrotoxicity in patients with cancer

OBJECTIVE

Cisplatin is a potent antineoplastic agent used and its major limiting side effect is nephrotoxicity. The aims of the study are early detection of acute kidney injury (AKI) with biomarkers and investigation of the potential nephron-protective effects of theophylline.

METHODS

Glomerular filtration rates (GFR), neutrophil gelatinase-associated lipocalin (NGAL), cystatin C were measured at 5th day of treatment in all of the patients. In addition, these parameters were measured repeatedly after the administration of cisplatin, at 2nd hour, 5th and 20th days.

PATIENTS

Sixty patients who are planned to receive cisplatin for the first time were included in the study. Patients were divided into two groups as Group 1 (n = 30) (standard treatment arm) and Group II (n = 30) (theophylline arm).

RESULTS

In both groups after the administration of cisplatin, GFR showed a significant decrease within time (p = 0.006). Urine NGAL levels were significantly high after 2 h of cisplatin administration (p < 0.001), no significant difference was observed between groups. However, when the time*group effects were considered together, higher NGAL levels were detected in the group not receiving theophylline (p = 0.025). After 5 days of cisplatin administration, urine protein levels were significantly higher in both groups (p < 0.001).

CONCLUSION

Results showed that urine NGAL level is a superior biomarker compared to serum creatinine and serum cystatin C in the detection of early AKI. Theophylline was found not to bring a complete protection for the kidneys, but less nephrotoxicity was developed when compared to the group not receiving theophylline.

Neurodegeneration and chronic renal failure in methylmalonic aciduria--a pathophysiological approach

In the last decades the survival of patients with methylmalonic aciduria has been improved. However, the overall outcome of affected patients remains disappointing. The disease course is often complicated by acute life-threatening metabolic crises, which can result in multiple organ failure or even death, resembling primary defects of mitochondrial energy metabolism. Biochemical abnormalities during metabolic derangement, such as metabolic acidosis, ketonaemia/ketonuria, lactic acidosis, hypoglycaemia and hyperammonaemia, suggest mitochondrial dysfunction. In addition, long-term complications such as chronic renal failure and neurological disease are frequently found. Neuropathophysiological studies have focused on various effects caused by accumulation of putatively toxic organic acids, the so-called 'toxic metabolite' hypothesis. In previous studies, methylmalonate (MMA) has been considered as the major neurotoxin in methylmalonic aciduria, whereas more recent studies have highlighted a synergistic inhibition of mitochondrial energy metabolism (pyruvate dehydrogenase complex, tricarboxylic acid cycle, respiratory chain, mitochondrial salvage pathway of deoxyribonucleoside triphosphate (dNTP)) induced by propionyl-CoA, 2-methylcitrate and MMA as the key pathomechanism of inherited disorders of propionate metabolism. Intracerebral accumulation of toxic metabolites ('trapping' hypothesis') is considered a biochemical risk factor for neurodegeneration. Secondary effects of mitochondrial dysfunction, such as oxidative stress and impaired mtDNA homeostasis, contribute to pathogenesis of these disorders. The underlying pathomechanisms of chronic renal insufficiency in methylmalonic acidurias are not yet understood. We hypothesize that renal and cerebral pathomechanisms share some similarities, such as an involvement of dicarboxylic acid transport. This review aims to give a comprehensive overview on recent pathomechanistic concepts for methylmalonic acidurias.

Adenosine and Kidney Function

In this review we outline the unique effects of the autacoid adenosine in the kidney. Adenosine is present in the cytosol of renal cells and in the extracellular space of normoxic kidneys. Extracellular adenosine can derive from cellular adenosine release or extracellular breakdown of ATP, AMP, or cAMP. It is generated at enhanced rates when tubular NaCl reabsorption and thus transport work increase or when hypoxia is induced. Extracellular adenosine acts on adenosine receptor subtypes in the cell membranes to affect vascular and tubular functions. Adenosine lowers glomerular filtration rate (GFR) by constricting afferent arterioles, especially in superficial nephrons, and acts as a mediator of the tubuloglomerular feedback, i.e., a mechanism that coordinates GFR and tubular transport. In contrast, it leads to vasodilation in deep cortex and medulla. Moreover, adenosine tonically inhibits the renal release of renin and stimulates NaCl transport in the cortical proximal tubule but inhibits it in medullary segments including the medullary thick ascending limb. These differential effects of adenosine are subsequently analyzed in a more integrative way in the context of intrarenal metabolic regulation of kidney function, and potential pathophysiological consequences are outlined.

Renal transplantation in a 14-year-old girl with vitamin B12-responsive cblA-type methylmalonic acidaemia

Renal tubular dysfunction and chronic renal failure are well recognised complications of methylmalonic acidaemia (MMA) and can occur even in the context of optimal medical metabolic management. Organ transplantation, such as renal and combined liver and renal transplants, have been utilised in the past for children whose disease cannot be managed by conservative medical practices and those with end stage renal disease. Our patient was diagnosed with B(12)-responsive MMA (subsequently proven to be cblA-type MMA) in the postoperative period following renal transplantation for idiopathic chronic renal failure. She remains well, with excellent graft function and metabolic control 4 years after transplantation. This patient highlights the importance of testing for the inborn errors of metabolism in patients presenting with recurrent acidosis and progressive renal impairment.

Mechanisms of adenosine-induced renal vasodilatation in hypertensive patients

BACKGROUND

Adenosine is an endogenous nucleoside with potent vasodilatory capacities, released under ischaemic conditions in particular. Its mechanisms of action, however, remain elusive.

OBJECTIVE

To evaluate the role of adenosine, using a non-selective purinergic receptor antagonist, and the possible involvement of nitric oxide in this mechanism. In addition, the production of renin and catecholamines was studied during infusion of adenosine, caffeine, or both.

METHODS

Thirty-three hypertensive patients who underwent diagnostic renal angiography received intrarenal infusions of adenosine either alone or in combination with caffeine or the nitric oxide synthase inhibitor, N-monomethyl-L-arginine (L-NMMA). The effects on renal blood flow (RBF) were assessed by the xenon-133 washout technique and both arterial and renal venous blood samples were taken for measurement of renin and catecholamine concentrations. Intra-arterial blood pressure and heart rate were monitored continuously.

RESULTS

Adenosine induced a dose-dependent vasodilatation. Caffeine alone did not change RBF, but shifted the dose-response curve of adenosine to the right during concomitant infusion of caffeine. RBF during combined infusion of L-NMMA and adenosine was not different from that during adenosine alone, but the decrease in renal vascular resistance was less pronounced during this combination. Renin secretion did not change during the infusion of either adenosine alone or adenosine in combination with caffeine. Catecholamine concentrations also did not change during any of the experiments.

CONCLUSIONS

Adenosine induces vasodilatation in the human hypertensive kidney and this effect is mediated by the adenosine receptor. Nitric oxide plays, at most, a minor part in the adenosine-induced vasodilatation. Furthermore, renin secretion is not affected by adenosine and caffeine.

Nephroprotection by theophylline in patients with cisplatin chemotherapy: a randomized, single-blinded, placebo-controlled trial

The aim of the present study was to assess the possible prevention of cisplatin-induced impairment of GFR by theophylline in patients with various malignancies. The trial design was parallel, randomized, single blinded, and placebo controlled. Patients received cisplatin at a dosage of 50 mg/m(2) either combined with etoposide, ifosfamide, and epirubicin or with paclitaxel and 5-fluorouracil/folinic acid with the usual precautions, including a standard hydration scheme before application of cisplatin in both arms. In the control arm, placebo was administered; in the verum arm, patients received theophylline in a loading dose of 4 mg/kg intravenously over 30 min before cisplatin, followed by 0.4 mg/kg per min over a minimum of 6 h, and then 350 mg three times daily orally for 4 consecutive days after completion of chemotherapy. GFR of each patient was assessed by renal clearance of inulin within 3 d before and at day 5 after cisplatin chemotherapy. Despite usual precautions, patients in the placebo group had a 21% decrease (range, 11 to 31%) of inulin clearance after a single cycle of cisplatin-containing chemotherapy (92.9 +/- 3.4 versus 71.8 +/- 3.5 ml/min; P < 0.01). Patients who received theophylline had no deterioration of GFR (91.5 +/- 3.7 versus 90.0 +/- 3.8 ml/min; P > 0.05). No adverse effects have been observed during theophylline application. Conventional precautions such as hydration and osmotic diuresis cannot prevent a significant decrease of GFR after a single cycle of cisplatin-containing chemotherapy. The prophylactic application of theophylline as an intravenous loading dose and oral maintenance regimen may preserve kidney function in terms of GFR.

No participation of adenosine A1 receptor in acute nephrotoxicity by 4-pentenoic acid administration in dogs

Intrarenal infusion of 4-pentenoic acid is known to lower renal cortical ATP content and cause a reduction in glomerular filtration rate (GFR). The alteration in nucleotide metabolism might augment the production of adenosine, thereby eliciting the fall in GFR. This study was conducted to examine whether 4-pentenoic acid stimulates renal production of adenosine, and if so, to examine the role of adenosine A1 receptor in the reduction of GFR by 4-pentenoic acid. With infusion of 4-pentenoic acid (1 micromol x kg(-1) x min(-1)) into the renal artery of anesthetized dogs, GFR gradually decreased and reached minimum at 60 min with values ranging from 33.9+/-2.2 to 20.2+/-2.8 ml/min. Neither renal blood flow nor mean arterial pressure was affected, but tubular reabsorption of water and sodium was significantly attenuated. Renal venous plasma concentration and urinary excretion of adenosine rose markedly (20-fold) without any change in arterial concentration, suggesting that renal adenosine production was augmented by 4-pentenoic acid. However, KW-3902 (8-(noradamantan-3-yl)-1,3-dipropylxanthine), a selective antagonist of the adenosine A1 receptor, did not affect the action of 4-pentenoic acid on GFR or renal handling of water and sodium. It is concluded that 4-pentenoic acid markedly increases renal adenosine production, but adenosine A1 receptor is not involved in the 4-pentenoic acid-induced nephrotoxicity.

Effects of long-term caffeine consumption on renal function in spontaneously hypertensive heart failure prone rats

Our previous studies supported the hypothesis that prolonged administration of caffeine to animals with high-renin hypertension causes progressive deterioration of renal function. However, thus far this hypothesis has been tested with only a few animal models of hypertension. The aim of this study was to test this hypothesis further by investigating the effects of long-term caffeine consumption on renal function in adult spontaneously hypertensive heart failure (SHHF/Mcc-fa(cp)) rats, another model of high-renin hypertension. Lean, male, 9-month-old SHHF/Mcc-fa(cp) rats were randomized to receive either normal drinking water (control group) or drinking water containing 0.1% caffeine (caffeine group) for 20 weeks. No changes in body weight, food and fluid intake, urine volume, and sodium and potassium excretion were found in conscious SHHF/Mcc-fa(cp) rats after 10 or 20 weeks of caffeine treatment. However, caffeine treatment accelerated the time-related decline in renal function and augmented urinary protein excretion. Ten weeks into the protocol, creatinine clearance was 3.6+/-0.4 and 5.7+/-0.9 L/kg/day in the caffeine group and control group, respectively (p<0.02), whereas 20 weeks into the study, creatinine clearance was similarly diminished in both groups. Proteinuria was greater in the caffeine group compared with the control group at both 10 (928+/-131 vs. 439+/-21 mg/kg/day, respectively; p<0.02) and 20 weeks (1,202+/-196 vs. 603+/-30 mg/kg/day, respectively; p<0.01) into the protocol. After 20 weeks, all animals were anesthetized and instrumented. Caffeine treatment for 20 weeks had no effects on blood pressure, heart rate, or vascular resistance in four examined vascular beds (abdominal aorta and renal, carotid, and mesenteric arteries). No changes in renal hemodynamics and electrolyte excretion were found, whereas significantly lower glomerular filtration rate (GFR; inulin clearance) and creatinine clearance (p<0.05) were observed in caffeine-treated animals. These data support our hypothesis that prolonged consumption of caffeine has adverse effects on renal function, in high-renin hypertension.

Natriuretic effect of an adenosine-1 receptor antagonist in cirrhotic patients with ascites

BACKGROUND & AIMS

The sodium and water retention and renal vasoconstriction exhibited by patients with cirrhotic ascites are similar to the changes observed by stimulation of renal adenosine 1 receptors. The aim of this study was to investigate the effects of FK352 (an adenosine 1 antagonist) on renal and systemic hemodynamics and renal function in cirrhotic patients with ascites.

METHODS

p-Aminohippuric acid and inulin clearance, urine flow rate, sodium and potassium excretion, and free water clearance were measured for 2 hours before and after FK352 administration. Cardiac output, systemic vascular resistance, plasma angiotensin II level, plasma renin activity, and noradrenaline, adrenaline, and adenosine 3', 5'-cyclic monophosphate (cAMP) levels were also measured before and after FK352.

RESULTS

Urine sodium excretion and urine flow rate increased after FK352 by a mean of 199.9% +/- 43.0% (P < 0.001) and 51.2% +/- 17.5% (P < 0.02), respectively. Plasma cAMP and angiotensin II levels and plasma renin activity also increased by 10. 8% +/- 3.2% (P < 0.01), 36.9% +/- 11.3% (P < 0.01), and 247.9% +/- 82.6% (P < 0.02), respectively. No change was detected in any other parameter.

CONCLUSIONS

The isokaliuretic improvement in natriuresis and diuresis suggests a role for adenosine 1 antagonism in the treatment of the renal abnormalities found in advanced cirrhosis.

Renal circulatory effects of adenosine in patients with chronic heart failure

OBJECTIVES

We sought to study the renal circulatory effects of adenosine in patients with chronic congestive heart failure (CHF).

BACKGROUND

Renal blood flow (RBF) is often reduced in patients with chronic CHF and may lead to decreased renal function. The cause of reduced RBF is multifactorial and involves systemic as well as local vasoregulatory mechanisms. Stimulation of renal adenosine A1 receptors in animal models has resulted in a significant vasoconstriction of afferent and efferent glomerular arterioles and deterioration of renal function. Although adenosine serum levels have been shown to be elevated in patients with CHF, their effect on the renal circulation in this patient population has not been studied.

METHODS

Nine patients with CHF from left ventricular systolic dysfunction were studied. The effects of adenosine at a dose of 10(-5) mol/liter infused directly into the main renal artery on heart rate, renal artery blood pressure, renal artery cross-sectional area (measured by intravascular ultrasound), renal Doppler blood flow velocity (measured by a Doppler flow wire in the renal artery), RBF and renal vascular resistance (RVR) were evaluated.

RESULTS

Infusion of adenosine resulted in no significant effect on heart rate or renal artery blood pressure but caused a substantial increase in RVR (11,204 +/- 1,469 to 31,494 +/- 3,911 dynes x s x cm(-5), p = 0.0005), which led to a marked fall in RBF in every patient (mean values 376 +/- 36 to 146 +/- 22 ml/m2, p = 0.0002). These changes in RVR and RBF were associated with no significant change in renal artery cross-sectional area (0.389 +/- 0.040 to 0.375 +/- 0.033 cm2, p = 0.3).

CONCLUSIONS

Stimulation of renal adenosine receptors in patients with CHF results in marked renal vasoconstriction that leads to an important reduction in RBF. Lack of change in renal artery cross-sectional area suggests that adenosine affects intrarenal resistance blood vessels rather than large conductance vessels. These results may indicate a rationale for investigation of renal adenosine receptor blockade for enhancement of RBF and improvement of renal function in patients with chronic CHF.

Sodium intake markedly alters renal interstitial fluid adenosine

Adenosine is produced locally in the kidney. Accumulating data suggest that adenosine plays a role in regulating renal functions. Using a microdialysis technique, we monitored adenosine levels in cortical and medullary renal interstitial fluid and urine after 5 days of diets containing low (0.15%), normal (0.28%), and high (4.0%) sodium. Samples were collected from anesthetized rats (n=5 for each diet). Microdialysis fluid was infused at a rate of 1 microL/min. Adenosine, measured by radioimmunoassay, was stable in the dialysate. During normal sodium intake, renal interstitial fluid adenosine estimated from the concentration in dialysate leaving the cortex was 63 +/- 6 nmol/L, which was significantly lower than in dialysate leaving the medulla (157 +/- 6 nmol/L, P<.01). The concentration of interstitial medullary adenosine was estimated to be 190 nmol/L. In rats consuming a low sodium diet, renal cortical and medullary dialysate adenosine concentrations were significantly decreased (P<.01) by 62.6% and 64.9%, respectively. Rats consuming a high sodium diet had renal cortical and medullary dialysate adenosine concentrations that were increased 18.2- and 18.9-fold, respectively (P<.01), compared with levels in rats on a low sodium diet. Similar to changes in dialysate adenosine, urinary adenosine concentration decreased during low sodium intake (P<.01) and increased during high sodium intake (P<.01). The higher adenosine levels in renal medullary than in cortical interstitial fluid may reflect its major renal site of generation. The changes in renal adenosine generation with sodium intake may reflect renal energy expenditure.

Exogenous adenosine triphosphate (ATP) preserves proximal tubule microfilament structure and function in vivo in a maleic acid model of ATP depletion

The hallmark of ischemic acute renal failure is a rapid and early decline in proximal tubule ATP. Since we have previously shown that over half of apical microfilament losses occur within the first 5 min of experimental ischemic injury, we postulated that microfilament (F-actin) structure and cellular location are dependent on cellular ATP levels. To test this hypothesis, we used maleic acid to selectively inhibit renal cortical ATP production in vivo. Maleic acid significantly decreased tissue ATP and apical F-actin in a dose-dependent manner relative to equimolar sodium chloride controls, yet higher doses of maleic acid quantitatively resulted in net actin polymerization, primarily in the cytoplasm. Functionally, maleic acid decreased glomerular filtration rate (GFR) and tubular reabsorption of sodium (TRNa) in a dose-dependent manner relative to sodium chloride controls. Administration of exogenous ATP resulted in significant increases in tissue ATP, net actin depolymerization, and relocation of F-actin from the cytoplasm back to the apical surface coinciding with increases in GFR and TRNa. Thus, ATP depletion induced by maleic acid resulted in significant cytoskeletal and functional alterations that were ameliorated by exogenous ATP. We therefore conclude that the structure and cellular location of F-actin necessary for normal functioning of proximal tubule cells in vivo is dependent on tissue ATP levels.

Adenosine receptors and signaling in the kidney

It is now generally accepted that adenosine is capable of regulating a wide range of physiological functions. Nowhere is the diversity of this action better illustrated than in the kidney. When adenosine binds to plasma membrane receptors on a variety of cell types in the kidney, it stimulates functional responses that span the entire spectrum of renal physiology, including alterations in hemodynamics, hormone and neurotransmitter release, and tubular reabsorption. These responses to adenosine appear to represent a means by which the organ and its constituent cell types can regulate their metabolic demand such that it is maintained at an appropriate level for the prevailing metabolic supply. Extracellular adenosine, produced from the hydrolysis of adenosine 5'-monophosphate and stimulated by increased substrate availability and enzyme induction, acts on at least two types of cell surface receptors to stimulate or inhibit the production of cyclic adenosine-3',5'-monophosphate and also acts in some renal cells to stimulate the production of inositol phosphates and elevation of cytosolic calcium concentration. To understand when and why this complicated system becomes activated, how it interacts with other known extracellular effector systems, and ultimately how to manipulate the system to therapeutic advantage by selective agonists or antagonists, requires a detailed knowledge of renal adenosine receptors and their signaling mechanisms. The following discussion attempts to highlight our knowledge in this area, to present a modified hypothesis for adenosine as a feedback regulator of renal function, and to identify some important questions regarding the specific cellular mechanisms of adenosine in renal cell types.

Renal tubular dysfunction in methylmalonic acidaemia

Renal tubular function was assessed in seven patients with methylmalonic acidaemia not responsive to vitamin B12. Five patients failed to concentrate their urine normally and in these patients the glomerular filtration rate was also reduced. Fractional excretion of sodium was increased in four patients, fractional excretion of potassium in one patient and in three there was a decreased tubular reabsorption of phosphate. Although possibly representing primary tubular damage these findings were thought to be consistent with adaptive changes secondary to the reduced glomerular filtration rate. Two patients had evidence of a defect of urinary acidification and several had a degree of hyporeninaemic hypoaldosteronism suggesting type 4 renal tubular acidosis. In one patient with a mild variant no renal disease was detected. Decreased renal function and tubular abnormalities were common in patients with methylmalonic acidaemia. It is likely that they are linked and essentially secondary to the tubulo-interstitial nephritis that is histologically demonstrable on renal biopsy. The failure of urinary concentrating ability and the disturbed urine acidification will contribute to the metabolic derangement during episodes of decompensation.

Distribution of 5'-nucleotidase in the renal interstitium of the rat

The hydrolysis of 5'-AMP by 5'-nucleotidase is the main source of adenosine. In various tissues adenosine is a local mediator adjusting the organ work to the available energy. In the kidney it regulates renal hemodynamics, glomerular filtration rate and renin release via specific receptors of the arteriolar walls. By immunocytochemistry we identified interstitial and tubular sites of 5'-nucleotidase in the rat kidney. In the interstitium the enzyme was detected only in the cortical labyrinth, the compartment that comprises all arteriolar vessels besides other putative targets of adenosine. The 5'-nucleotidase-positive cells of the interstitium were identified as fibroblasts. The fibroblasts are in close contact with the tubules as well as with the vessels. Thus, any 5'-AMP released by the tubules into the interstitial space would be converted to adenosine in the direct vicinity of its assumed targets. Adenosine produced by tubular cells would hardly have access to its known targets, since 5'-nucleotidase is restricted to the luminal cell surface. Pathological events affecting the fibroblasts might influence renal function by modifying the interstitial adenosine production.

Chronic renal failure in methylmalonic acidaemia

The renal function of 12 patients with non vitamin B12 responsive methylmalonic acidaemia has been investigated. Eight patients had reduced glomerular filtration rates, but the plasma creatinine concentration was only raised in those with values of less than 40 ml/min per 1.73 m2 surface area. The reduction in glomerular filtration was a function of the age and the severity of the disease. Plasma urate concentrations were increased in four patients but this may be secondary to the renal disease rather than its cause.

Endogenous intrarenal adenosine preserves renal blood flow in one-kidney, one clip rats

Intrarenal adenosine concentration is threefold greater in the one-kidney, one clip hypertensive rat compared with normotensive animals. Since exogenously administered adenosine may increase renal blood flow by direct vasodilation, inhibition of renin release, or prejunctional interruption of adrenergic neurotransmission, these studies examined whether endogenous intrarenal adenosine maintains renal blood flow distal to renal arterial stenosis. Administration of theophylline, which blocks the direct vasodilating effect of adenosine and antagonizes the inhibitory effect of adenosine on renin release and sympathetic neurotransmission, resulted in marked renal vasoconstriction in one-kidney, one clip hypertensive animals. This theophylline-induced renal vasoconstriction was markedly attenuated by angiotensin II blockade with saralasin and was unchanged by renal denervation or beta 1-adrenergic blockade with atenolol. These findings indicate that the marked renal vasoconstriction in one-kidney, one clip hypertension during theophylline administration is mainly mediated by angiotensin II, is to a lesser degree due to inhibition of adenosine-induced vasodilation, and is independent of sympathetic influences. These data suggest that endogenous interstitial adenosine preserves renal blood flow in one-kidney, one clip hypertension mainly by inhibiting renin release.