Carbohydrate metabolism and uraemia-mechanisms for glycogenolysis and gluconeogenesis

Role of quercetin on hepatic urea production in acute renal failure

Acute renal failure (ARF) is a serious damage of renal function induced by various nephrotoxic drugs, ischemia, bilateral urethral obstruction, trauma and unilateral nephrectomy. Dramatic clinical syndrome, azotemia, develops as a result of hypovolemia, oliguria, reduced glomerular filtration and acidosis. In addition to classic medications recent studies give more attention to beneficial effect of natural plant products as bioflavonoids. We have studied the influence of bioflavonoid, quercetin, on hepatic urea production in glycerol induced ARF in the rats. Male Sprague Dawley rats were used in the experiment. The value of urea production in the liver was determined by measuring of liver arginase activity, the terminal enzyme of urea cycle. Arginase activity was increased (p < 0.01) as well as urea level (p < 0.001) 48 h after glycerol administration. Pretreatment by quercetin suppressed the arginase activity in the liver (p < 0.05) and plasma levels of urea (p < 0.01). So, we have concluded that quercetin may be beneficial in glycerol induced ARF.

Glucose-induced insulin secretion in uremia: effects of aminophylline infusion and glucose loads

To explain mechanisms responsible for derangement of insulin release in uremia, we investigated glucose metabolism through three different tests in 14 patients with end-stage chronic renal failure. These tests were: intravenous glucose tolerance test with 0.33 g/kg of glucose solution (IVGTT); IVGTT with 0.5 g/kg of glucose solution (IVGTT2); IVGTT during aminophylline infusion (IVGTT + A). Twelve of the patients had IVGTT repeated after two to four months of thrice-weekly regular hemodialysis (IVGTT3). In each test we measured plasma glucose (G), immunoreactive insulin (IRI) and C-peptide. We also calculated glucose constant decay (K), insulin production (IRI area), insulinogenic index (IGI), and insulin resistance index (RI). Twenty-nine healthy volunteers formed the normal controls for IVGTT. As compared to controls, during IVGTT uremic patients showed significantly lower values in K, IRI area and IGI, and showed a significant RI value increase. During IVGTT2, IRI are values were higher than during IVGTT but IGI and K values were unchanged. During IVGTT + A both IRI area and IGI values were higher than during IVGTT. After hemodialysis treatment (IVGTT3) K, IRI areas and IGI increased significantly as compared to the predialysis period. K increase after hemodialysis correlated directly to IGI increase and inversely to RI changes. IGI increase during IVGTT3 was directly correlated to IGI rise during IVGTT + A. From these data we infer that defective insulin release in uremia is due to a decrease of beta-cell glucose sensitivity rather than to their functional exhaustion. An impaired adenyl cyclase-cAMP system may have an important role in the pathogenesis of this abnormality.

Normalization of enhanced hepatic gluconeogenesis by the antiglucocorticoid RU 38486 in acutely uraemic rats

Hepatic amino acid uptake, urea and glucose production are increased in acute uraemia. It has been shown that this metabolic pattern is mediated by glucocorticoids. Accordingly, the administration of the antiglucocorticoid RU 38486 to acutely uraemic rats resulted in a reduction of serum urea-N and glucose levels. To clarify whether this effect is due to a reduction in hepatic gluconeogenesis we examined the effect of the antiglucocorticoid RU 38486 on urea and glucose formation in isolated hepatocytes from sham-operated (SHAM) and bilaterally nephrectomized (BNX) rats receiving RU 38486 or the vehicle only. Hepatic glucose production in BNX rats was considerably increased from Na-pyruvate (+79%), alanine (+174%), glutamine (+158%), and serine (+87%) compared with SHAM animals. Concomitantly, hepatic urea formation was also enhanced from amino acid substrates in acutely uraemic rats. When uraemic animals were treated with RU 38486, glucose production from amino acids and Na-pyruvate was reduced to the range of SHAM animals or even lower. This effect could not be demonstrated in SHAM-operated controls. A comparable decrement in hepatic urea production was observed in BNX rats treated with the antiglucocorticoid. Thus, glucocorticoids appear to play a key role in the abnormal hepatic urea and glucose production of acutely uraemic rats.

Effect of nifedipine on carbohydrate metabolism in the rat

The potential role of an oral administration of nifedipine was investigated in the rat. Therefore, animals were fed on a nifedipine-containing or control diet for 12 days. Nifedipine caused a significant decrease of liver glycogen (47.9 +/- 4.9 vs 132.6 +/- 17.1 micrograms/mg protein), whereas liver glucose (213.1 +/- 15.3 vs 110.4 +/- 6.4 micrograms/mg) and lactate (44.8 +/- 4.1 vs 26.5 +/- 1.8 nmol/mg) concentrations increased. Various concentrations of nifedipine failed to influence glycogenolysis but stimulated gluconeogenesis in isolated rat hepatocytes. Blood lactate and pyruvate levels were significantly elevated in the nifedipine pretreated rats, whereas ketone bodies remained constant. Nifedipine pretreatment also increased the rates of excretion of various electrolytes and water followed by significantly lower plasma sodium, potassium, phosphate, and normal glucose values. We conclude that nifedipine-induced liver glycogenolysis may deteriorate glucose tolerance in patients with an already impaired carbohydrate metabolism.

Long-term effects of nifedipine on carbohydrate and lipid metabolism in hypertensive hemodialyzed patients

To evaluate long-term effects of nifedipine on carbohydrate and lipid metabolism, 15 hypertensive patients undergoing regular hemodialysis treatment were investigated before nifedipine therapy, after 3 and 9 weeks, and 2 weeks after stopping nifedipine therapy. Three weeks following the administration of nifedipine, both glucose and insulin concentrations decreased significantly from 102.1 +/- 2.6 to 94.9 +/- 2.2 mg/dl and from 19.9 +/- 2.9 to 13.9 +/- 1.7 microU/ml and also remained significantly lower after 9 weeks of nifedipine therapy. This effect was paralleled by a fall of noradrenaline and dopamine. Glucagon levels remained constant. Glucose tolerance tests performed during nifedipine medication and 2 weeks after stopping of nifedipine therapy did not differ significantly. An increase of pyruvate, citric acid cycle intermediates, and ketone bodies--but not of lactate--was registered during nifedipine medication. The observed effects were not completely abolished after the 2-week placebo phase. Our data indicate that nifedipine lowers serum glucose values despite decreased insulin and constant glucagon levels in hypertensive hemodialyzed patients. Considering additionally the behavior of catecholamines and organic acids, the effects could be explained by the improvement of peripheral glucose utilization.

[Alterations of fat metabolism in renal disease - pathogenetic mechanisms (author's transl)]

Hypertriglyceridaemia is often observed in patients (1) with chronic renal insufficiency, (2) on haemodialysis and (3) after successful renal transplantation. HDL cholesterol is reduced in all three groups of patients and plasma cholesterol is elevated after renal transplantation. In these three patient groups type IV hyperlipoproteinaemia is found most frequently and after renal transplantation there is a relative increase in the incidence of type II hyperlipoproteinaemia. The role of glucagon resistance and carnitine deficiency in the alteration of fat metabolism seen in patients with chronic renal failure and patients on haemodialysis is discussed. Other factors which may influence fat metabolism in uraemia include calcium and vitamin D status as well as beta adrenergic receptor blocking agents and diuretics. Steroid therapy may be one cause of the hypercholesterolaemia and hypertriglyceridaemia seen after renal transplantation. PHLP lipase activity is reduced in all three groups of patients. In nephrotic syndrome, if hypercholesterolaemia occurs, the HDL cholesterol fraction is increased and thus the cardiovascular risk may be lower than in the three patient group mentioned above.

Inactivation of urinary kallikrein by alpha 1-antitrypsin

Proteolytic activity, with azocasein as substrate in the presence and absence of 0.4 IU kallikrein (Padutin) was measured in the 24 h urine fractions of 100 ambulatory patients with hypertension, proteinuria or haematuria. Urinary protein and alpha 1-antitrypsin concentration have also been assayed. There was an inverse relationship between kallikrein activity and urinary alpha1-antitrypsin concentration( r = 0.84; y = 39.2 e-0.009x). Furthermore, kallikrein activity and 24 h urinary alpha 1-antitrypsin excretion were also inversely correlated (r = 0.81; y = 886,4 e-0.011x). Our data suggest an inactivation of renal kallikrein by urinary alpha 1-antitrypsin.

Evidence for the participation of proteases on protein catabolism during hypercatabolic renal failure

In ultrafiltrated plasma (molecular weight less than 50,000) obtained from four patients with multiple muscular trauma and acute post-traumatic renal failure, it was possible to verify a subcomponential specific digestion of the subunits alpha and gamma of phosphorylase kinase isolated from rabbit skeletal muscle. The activity of free proteolytic enzymes in ultrafiltrated plasma as well as an increase of plasma alpha 1-antitrypsin values were correlated with the severity and unfavourable course of the illness. In contrast, the plasma levels of alpha 2-macroglobulin were drastically lowered. The mean total protein concentration in the sera of patients with post-traumatic ARF was lowered, whereas the mean ultrafiltrate protein concentration was significantly enhanced. In ultrafiltrated plasma of two patients with hyperuricaemic ARF, three patients with ARF after drug over-dosage, one patient with acute pancreatic necrosis combined with acute renal failure and one patient with chronic pancreatitis, no proteolytic activity could be detected using phosphorylase kinase as substrate. Studies on the trypsin binding capacity of the plasma protease inhibitors revealed a significantly lowered level in patients with post-traumatic acute renal failure as compared to healthy controls, patients with chronic renal insufficiency and patients on regular dialysis treatment Proteolytic activity was found in ca. 100-fold concentrated diafiltrates (molecular weight greater than 10,000) of patients on regular dialysis treatment. Our data suggest a participation of proteases on protein catabolism in hypercatabolic states. Whilst the blood coagulation system can largely be excluded as a source of proteases, it is possible that proteolytic enzymes may be released from muscle lysosomes and/or macrophages after multiple muscular trauma.