Gernot Peter

Evidence for reduced catabolism by the antiglucocorticoid RU 38486 in acutely uremic rats

Previous studies suggested that increased blood levels of, or increased tissue sensitivity to, glucocorticoids may contribute to catabolism in acute uremia. To examine this possibility we determined urea nitrogen (urea-N) appearance, plasma levels of Nt-methylhistidine and the activity of the alkaline myofibrillar proteinase in acutely uremic rats with and without treatment with RU 38486, a selective antiglucocorticoid. Forty-eight hours after bilateral nephrectomy, the rats had markedly elevated serum levels of urea-N, creatinine, potassium and phosphorus. In uremic rats receiving RU 38486, comparable levels of serum creatinine were found, but the serum levels of urea-N (221 +/- 4 vs. 259 +/- 5 mg/dl) and phosphorus (6.5 +/- 0.3 vs. 8.5 +/- 0.4 mmol/l) were significantly decreased as compared to uremic animals without RU 38486. In comparison to sham-operated rats, urea-N appearance (net urea production) was increased by 56% 48 h after bilateral nephrectomy. This increment was almost completely reversed in uremic animals receiving the antiglucocorticoid. In untreated uremic rats, plasma levels of Nt-methylhistidine were 10.3 +/- 0.9 microgram/dl, whereas the administration of RU 38486 caused a significant decline in the levels of this amino acid (7.6 +/- 0.5 microgram/dl). This reduction in Nt-methylhistidine was associated with a concomitant decrease of myofibrillar proteinase activity in muscle tissue homogenates. Compared to sham-operated animals, this proteinase activity was increased by 30% in uremic rats, but was normal in those given RU 38486. Taken together, these data support the view that in acute uremia accelerated ureagenesis occurs, while enhanced muscle protein breakdown, owing to an increment in myofibrillar proteinase activity, provides the necessary amino acid precursors.(ABSTRACT TRUNCATED AT 250 WORDS)

Reduction of Urea Generation and Muscle Protein Degradation by Adrenalectomy in Acutely Uremic Rats

The effect of adrenalectomy on the enhanced protein degradation in acute uremia was investigated. Therefore, serum urea nitrogen, urea N appearance and Nt-methylhistidine were followed in bilaterally nephrectomized rats. At 48 h after induction of uremia the animals displayed serum urea nitrogen levels of 223 +/- 9.5 mg/dl as compared to 26.0 +/- 1.0 mg/dl in sham-treated rats. This increment was significantly attenuated in acutely uremic, adrenalectomized animals (176 +/- 6.0 mg/dl). When these rats were substituted with corticosterone (5 mg/kg body weight), serum urea nitrogen readily increased to levels of acutely uremic animals with intact adrenal glands (225 +/- 6.0 mg/dl). The net generation of urea, as determined by the urea N appearance, was significantly increased during acute uremia (370 +/- 26 mg/48 h) as compared to SHAM animals (220 +/- 15 mg/48 h). This increment of urea formation could almost be completely reversed by simultaneous adrenalectomy (238 +/- 20 mg/48 h). When these rats were substituted with corticosterone, the urea N appearance rebounded to values quite comparable to acutely uremic rats with intact adrenal glands (363 +/- 30 mg/48 h). To determine whether skeletal muscle proteins might serve as a source for the enhanced protein degradation in acute uremia, plasma levels of Nt-methylhistidine were measured. Bilaterally nephrectomized rats had Nt-methylhistidine values of 9.6 +/- 1.0 micrograms/ml. In acutely uremic rats without adrenal glands, Nt-methylhistidine levels were found to be significantly decreased (6.0 +/- 0.4 micrograms/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic ethanol ingestion enhances catabolism and muscle protease activity in acutely uremic rats.

Skeletal muscle wasting in men as well as enhanced urea production in animals due to ethanol consumption has been demonstrated by numerous authors. Furthermore, the outcome of acute renal failure is closely related to the extent of catabolism. The present study was performed to investigate whether chronic ethanol exposition prior to binephrectomy (BN) may represent a predisposing factor for enhanced protein breakdown. Rats underwent BN after exposure to ethanol or isocaloric substrate for 4 weeks. Blood chemistries and muscle samples were obtained 48 h after BN. Animals fed with ethanol revealed significantly higher levels of serum urea nitrogen (SUN) and urea nitrogen appearance (UNA) in comparison to controls. Preconditioning on ethanol-derived calories induced an accelerated fractional degradation rate of myofibrillar protein as demonstrated by a significantly enhanced serum Nt-methylhistidine/creatinine ratio. The increase in serum indicators of enhanced myofibrillar breakdown correlated with the stimulated activities of alkaline myofibrillar protease and cathepsin B. Finally, serum corticosterone levels were enhanced in the experimental group in comparison to controls, indicating an ethanol-related adrenocortical stimulation to be a possible mediating factor of enhanced catabolism in ARF. Thus, chronic ethanol intake prior to the onset of ARF seems to be a risk factor for enhanced catabolism in the course of acute uremia.

Independence of enhanced protein catabolism from glucocorticoids in chronically uremic rats

SummaryPatients with chronic renal failure are prone to develop negative nitrogen balance resulting clinically in wasting and malnutrition. To study the role of glucocorticoids in the pathogenesis of uremic catabolism, we determined urinary excretion rates of urea and Nt-methylhistidine in chronically uremic rats with and without RU 38 486, a potent antiglucocorticoid. In comparison to pair-fed non-uremic animals, chronically uremic rats displayed significantly enhanced ureagenesis, as demonstrated by increased urinary urea excretion, and myofibrillar protein breakdown, as indicated by increased excretion rates of urinary Nt-methylhistidine. The administration of RU 38486 to chronically uremic rats, however, did not result in a normalization of urinary excretion of Nt-methylhistidine. Similarily, the antiglucocorticoid did not influence the extent of ureagenesis in our uremic animals, as it was demonstrated by comparable levels of urinary urea excretion. This suggests that glucocorticoids are not involved in the pathogenesis of enhanced catabolism in chronic renal insufficiency.

Catabolic Effects of Ethanol in Chronically Uremic Rats

Both ethanol consumption and uremia are considered to be associated with wasting, malnutrition and debilitation. The present study was designed to investigate as to whether ethanol exerts a stimulatory effect on the catabolic state of renal failure. Rats underwent 5/6-nephrectomy and were fed either with or without ethanol. The degree of uremia was comparable in both groups. Ethanol-fed uremic rats, however, displayed higher serum levels of urea (+ 103%) and glucose (+29%), as compared to uremic animals without alcohol. Subsequently, the urea N appearance was enhanced (+60%) in uremic rats with alcohol as compared to uremic animals without alcohol. In sham rats urea N appearance was also increased (+39%) following ethanol administration in comparison to sham-operated rats without alcohol, albeit to a lesser degree. Urinary Nt-methylhistidine excretion, an indicator of myofibrillar protein breakdown, was enhanced throughout the experiment in uremic rats receiving ethanol. Finally, ethanol caused higher urinary excretion rates of corticosterone in uremic animals as compared to uremic rats without ethanol. There was a significant correlation between urinary corticosterone excretion and both urea N appearance and urinary Nt-methylhistidine excretion. We conclude that ethanol consumption further aggravates the catabolic state of uremia and that this is mediated by an increment in glucocorticoid production.

Catabolism in Acute Renal Failure: Importance of Glucocorticoids and Lysosomal Enzymes

Renal failure has been previously shown to be a catabolic event1–6. There is growing evidence for a certain role of proteolytic enzymes in the catabolism of acute uremia7–13 Thus, frank proteolytic activity has been demonstrated in ultrafiltrated plasma fractions, in the urine and bronchoalveolar-lavage (BAL) fluid14–15 The type of proteinases involved, is up to now not totally defined. There are some data, which indicate a participation of broad spectrum serine proteinases in the BAL-fluid and in the plasma of ureter-ligated rats16.

HORMONAL REGULATION OF MUSCLE PROTEIN CATABOLISM IN ACUTELY UREMIC RATS: EFFECT OF ADRENALECTOMY AND PARATHYROIDECTOMY

To examine the role of glucocorticoids and PTH on the enhanced protein catabolism of acute uremia, rats were rendered uremic and had their adrenals or their parathyroid glands concomitantly removed. Adrenalectomy resulted in a marked reduction of urea generation in uremic animals due to decrease of myofibrillar protein breakdown as indicated by lower serum levels of Nt-methylhistidine and a reduction in the activity of the myofibrillar proteinase from skeletal muscle. This reduced urea formation was accompanied by marked hypoglycemia. Parathyroidectomy, on the other hand, caused no change of those parameters of protein catabolism, suggesting that PTH does not account for the protein degradation observed in acutely uremic rats.

Eglin C fails to reduce catabolism in acutely uremic rats.

Increased release of proteinases from polymorphonuclear leukocytes, namely elastase, has been incriminated to take part in the pathogenesis of enhanced muscle protein breakdown in acute renal failure. In order to investigate, whether inhibition of the granulocyte proteinase elastase and cathepsin G would have a beneficial effect on the extent of muscle protein degradation, eglin C, a potent inhibitor of the granulocyte proteinase elastase and cathepsin G, was administered intraperitoneally to acutely uremic rats. 48 hours after bilateral nephrectomy, eglin C-treated animals displayed no significant difference, as far as serum levels of SUN, glucose and Nt-methylhistidine are concerned. Similarly, eglin C treatment failed to reduce the stimulated activity of the alkaline myofibrillar proteinase in comparison to binephrectomized controls. Hence, according to these results, granulocyte proteinases do not seem to be an important mediator of uremic catabolism, since their inhibition by eglin C does not reduce enhanced protein breakdown in acutely uremic rats.

Evidence for the Role of Proteinases in Uremic Catabolism

Enhanced muscle protein breakdown has been demonstrated in acutely uremic rats by numerous authors. In order to investigate the pathogenetic role of skeletal muscle proteinases leupeptin, a low-molecular weight proteinase inhibitor, was administered intraperitoneally to acutely uremic rats. Twenty-four hours after bilateral nephrectomy, leupeptin-treated animals displayed significantly lowered serum urea levels (-32%), as compared to untreated uremic rats. As a sign of muscle protein breakdown, plasma levels of Nt-methylhistidine, an indicator of myofibrillar protein degradation, were also decreased (-35%) in the uremic animals treated with leupeptin as compared to untreated uremic rats. Finally, leupeptin treatment resulted in a significant inhibition of the myofibrillar alkaline proteinase activity, a proteinase which has been related to various catabolic conditions. These findings suggest that the increased muscle protein breakdown in uremia is caused by enhanced activity of muscular proteinases and that anti-proteolytic agents display favourable effects on the enhanced protein degradation observed in acute uremia.

Prostaglandin synthetase inhibitors are not beneficial in the hypercatabolic state of acute uremia in rats

SummaryIn rats the effect of prostaglandin synthetase inhibition on the enhanced protein degradation in acute uremia was investigated. After 48 h of bilateral nephrectomy the urea nitrogen appearance, an indicator of net protein degradation, was calculated, andNτ-methylhistidine (Nτ-MH) serum concentration was measured for judging myofibrillar breakdown. Also serum urea nitrogen, creatinine, and potassium serum concentrations were followed up. All bilateral nephrectomized rats showed severe uremic disturbances with increased (P < 0.01) concentrations of serum urea nitrogen, creatinine, and potassium. Moreover, the urea nitrogen appearance andNτ-MH serum concentration increased (P < 0.05) significantly. Administration of indomethacin (4 mg · kg−1 b.wt./12 h i.p.) in bilateral nephrectomized rats did not influence the analyzed parameters significantly. Thus, we could not demonstrate a positive influence on the increased skeletal muscle degradation in acutely uremic rats by prostaglandin synthetase inhibition. These data suggest that in our model of acute uremia prostaglandins do not play a major role in the degradation of striated muscle.