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Abetraet. The effect of acute uraemia on glucose and urea formation by isolated perfused liven of fasting rats was investigated.The basal gluconeogenesis following nephrectomy was significantly increased as compared to normal and sham operated controls. Enhanced glucose formation was associated with an increase in both urea synthesis and output of the p r l y metabolizable amino acids valine, leucine, and isoleucine. In the presence of a mixture of amino acids (serine, threonine, lysine, glutamic acid, ornithine, and citrnlline) all added at near physiological concentrations, the stimulating effect of uraemia on gluconeogenesis was further enhanced. This was paralleled by an increased formation of urea and an increased uptake of the amino acids. It is concluded that acute uraemia may stimulate glucose synthesis by increased substrate supply. This seems to be achieved by a t least two different mechanisms, namely increased protein degradation and accelerated amino acid utilization.

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The activities of urea-cycle enzymes were measured in liver biopsies of patients suffering from chronic-persistent hepatitis (CPH), chronic-active hepatitis (CAH) and liver cirrhosis. Most of the activities of urea-cycle enzymes did not differ in the case of CPH as compared to controls. Chronic-active hepatitis and liver cirrhosis are associated with a significant (p less than 0.05) decrease of enzyme activity as compared to normal persons. Most of the urea-cycle enzymes are significantly decreased in patients with CAH in comparison with CPH. No significant differences can be demonstrated in the case of CAH as compared to patients with complete cirrhosis. In conclusion, progression of chronic liver disease is associated with increasing alterations of enzyme activities catalyzing a liver specific metabolic pathway. The decrease of the activities of the key enzymes of the urea cycle (Carbamylphosphate-Synthetase and Arginino-succinate-Synthetase) is nearly identical both in CAH and liver cirhosis, although CAH may be a reversible disease. Therefore, marked alterations in the metabolic pathway of ammonia detoxification seem to preceed the histological manifestation of irreversible liver damage.

Abetraet. The effect of acute uraemia on glucose and urea formation by isolated perfused liven of fasting rats was investigated.The basal gluconeogenesis following nephrectomy was significantly increased as compared to normal and sham operated controls. Enhanced glucose formation was associated with an increase in both urea synthesis and output of the p r l y metabolizable amino acids valine, leucine, and isoleucine. In the presence of a mixture of amino acids (serine, threonine, lysine, glutamic acid, ornithine, and citrnlline) all added at near physiological concentrations, the stimulating effect of uraemia on gluconeogenesis was further enhanced. This was paralleled by an increased formation of urea and an increased uptake of the amino acids. It is concluded that acute uraemia may stimulate glucose synthesis by increased substrate supply. This seems to be achieved by a t least two different mechanisms, namely increased protein degradation and accelerated amino acid utilization.

Abstract. Enzyme activities of the glycolytic, gluconeogenic, and hexose monophosphate pathways were measured in the liver of starved rats 12 and 48 hours after bilateral nephrectomy. Control experiments (sham operated rats) revealed that alterations of enzyme activities were not due to uraemia but to starvation. Alanine‐aminotransferase and aspartate‐ aminotransferase activities, however, were significantly elevated in rat liver 48 hours after nephrectomy when compared with sham operated controls. Concentrations of some of the gluconeogenic intermediates (3‐phosphoglyceric acid, pyruvate, phosphoenolpyruvate and glucose‐6‐phosphate) were significantly higher in the liver of uraemic animals. Amino acid analysis showed an increase in only L‐alanine concentration. It is suggested that the elevated content of pyruvate in the liver during acute uraemia is due to an inhibition of pyruvate degradation. Together with the elevated pyruvate concentration the increase in L‐alanine could be explained as a consequence of the equilibrium of the alanine‐aminotransferase reaction; Kapp. of the reaction is not changed by uraemia. Increased activities of the transaminases and the elevated concentrations of the other metabolites measured might indicate that in the liver of nephrectomized rats there is enhanced gluconeogenesis from substrates other than pyruvate.

1. Urea cycle enzymes and ornithine ketoacid transaminase were extracted from rat liver using various buffer systems and different procedures for the mechanical disintegration of the cells. Of the buffers tested, phosphate and glutathipne gave optimal results, whereas significant differences were found when other extracting media were used: activities of ornithine ketoacid transaminase and ornithine carbamyl transferase were significantly decreased in triethanolamine-and in tris-[hydroxymethyl]-amiiiomethane (tris)-buffer when compared with phosphate. Arginase activity remains unchanged in phosphate and in tris-buffer, but it decreased significantly in triethanolamine-buffer. With the exception of ornithine ketoacid transaminase, no significant increase of enzyme activities were found when livers were extracted with 0.1 % cetylammonium bromide and distilled water respectively. Carbamylphosphate synthetase from rat liver was inactive in the presence of phosphate ions as was ornithine ketoacid transaminase when glutathione (1 mmol/1 GSH) was added to the extracting medium. With the exception of Carbamylphosphate synthetase, all other enzymes tested showed significantly higher activities in liver homogenates than in 100 000 g supernatants. 2. Optimal extraction of urea cycle enzymes from small specimens (e. g. liver biopsies) could be achieved by disintegrating the tissue in an micro all-glass homogenizer, followed by ultrasonic treatment. The use of cetylammonium bromide and the reextractipn of bioptic specimens could be avoided. In contrast, larger tissue samples (500 mg and more) must be reextracted for the complete elution of urea cycle enzymes. 3. Urea cycle enzymes and ornithine ketoacid transaminase were differentiated according to the intracellular localisation by the method of fractional tissue extraction. It could be demonstrated that ornithine ketoacid transaminase, Carbamylphosphate synthetase and ornithine carbamyl transferase were of mitochondrial origin, whereas arginino'succinate lyase activity was found exclusively in the extramitochondrial cell compartment. Arginase activity could be measured mainly extramitochondrially, most probably bound to subcellular structures. However it could not be excluded that at least a small amount of this enzyme was of mitochondrial origin.

The role of L(+) lactic acid in the metabolism of individual cells and also in organized cell systems is defined by the concepts of "fermentation" and "oxygen debt." Both expressions, which are derived from the early days of physiological cell research, point already toward the close relationship of lactic acid to the oxydation systems of the cell, which will be the subject matter of the following.We owe the first systematic studies of the lactic/pyruvate Red/Ox-system to Huckabee,' who showed that the lactate/pyruvate ratio in the human blood remains extraordinarily constant, even when the total amount of lactate and pyruvate had risen over the normal value that could be obtained by pyruvate or bicarbonate infusion. Only under condition? under which the organism enters into an oxygen debt, as, for instance, during muscular work, Huckabee' found a rise of the lactate/pyruvate ratios too. This was, together with the difference of the lactate and pyruvate level, brought into a quantitative relationship to the oxygen debt and was termed "excess lactate." Huckabee assumed further that the lactate/pyruvate system, because of its ability to permeate through cell walls, would reflect the reduction state of ,the nicotinamidedinucleotide-system (NAD/NADH) in the cells of the body. Especially so since one could expect, because of the final position of the lactatedehydrogenase reaction in the Embden-Meyerhof system, a very close approximation of the steady state of lactate/pyruvate to the static equilibrium position with the NAD/NADH system. Holzer eta1.3 arrived a t the same conclusion for the analogous system acetaldehyde/ethanol in fermenting baker's yeast; also Czok,' from Buecher's Marburg group, related arteriovenous differences of lactate and pyruvate in the human brain to the NAD/ NADH ratio inside the brain cells. Undoubtedly, as Huckabee already has emphasized, it is not possible to count on a uniform state of reduction of the NAD/NADH system in all the different tissues and cells of the body. Therefore, the postulated relationship between the lactate/pyruvate ratio in the blood and the state of reduction of the NAD/NADH system inside the cells of the body requires a further differentiated analysis.Asa matter of fact the measurement of lactate and pyruvate in various tissues of the rat under conditions that permit an adequate fixation of the in vim state of the metabolites shows differences both in their total amounts and 974