Renal arginine metabolism in fasted rats with subacute short bowel syndrome

1. Arginine can be produced in the kidney from citrulline. An important source of circulating citrulline is the intestinal breakdown of glutamine. Consequently, partial enterectomy leads to decreased plasma citrulline levels. The aim of the present study was to investigate the effect of diminished arterial citrulline levels on renal arginine production and total-body free arginine pools.2. Renal amino acid metabolism was studied 24 h after 75% small bowel resection in rats fasted overnight (16 h) (n=12; total fast 40 h). Sham-operated (n=9) and non-operated 16-h and 40-h fasted controls were studied in parallel (n=8/n=7). During anaesthesia, L-(2, 3-3H)-arginine and para-aminohippuric acid were infused until steady state. Subsequently, arterial and renal venous blood samples were taken. Concentrations of para-aminohippurate and amino acids and specific activity of arginine and citrulline were measured to calculate renal plasma flow, net renal uptake or release, and unidirectional influx or efflux of arginine and citrulline, as well as whole-body arginine turnover.3. Arterial citrulline was decreased in enterectomized rats compared with sham-operated rats (23+/-3 versus 44+/-6 microM). Net renal citrulline uptake and arginine release were almost stoichiometric (-36+/-7 and 38+/-6 nmol.min-1. 100 g-1 body weight respectively in sham-operated rats) and were both diminished by 50% in enterectomized versus sham-operated rats. In all groups, net renal arginine production accounted for less than 10% of whole-body rate of arginine appearance (488 nmol.min-1.100 g-1 body weight in the sham group). Despite decreased net renal citrulline consumption and renal arginine production in enterectomized rats, whole-body rate of arginine appearance and arterial arginine did not change significantly.4. In conclusion, net renal arginine production is reduced 24 h after 75% enterectomy in fasted rats. However, this does not have important effects on whole-body arginine production.

[Pseudomyxoma peritonei]

Pseudomyxoma peritonei was diagnosed in 3 men aged 38, 66 and 54 years with weight loss and distension of the abdomen. Pseudomyxoma peritonei results from seeding of the peritoneal cavity with mucus-producing epithelium. The disease is traditionally characterized by accumulation of huge amounts of mucinous ascites, relatively long survival and absence of distant, extraperitoneal metastases. Mostly, the primary tumour is an appendicular adenoma or adenocarcinoma. Sometimes, the primary tumor is localized in the ovaries. Extensive surgical debulking with postoperative intraperitoneal chemotherapy appears to be the treatment of choice.

Effects of simulated upper gastrointestinal hemorrhage on ammonia and related amino acids in blood and brain of chronic portacaval-shunted rats

Gastrointestinal (GI) hemorrhage during compromised liver function is known to precipitate portal-systemic encephalopathy (PSE). Hypothetically, the induced hyperammonemia depletes cerebral glutamate pools. To investigate this hypothesis, rats were studied 14 days after portacaval shunt (PCS) or sham surgery (SHAM). Rats received 3 mL bovine erythrocytes or saline at t = 0, 1, 2, and 3h via a previously placed gastrostomy catheter. At t = 0, 2, 4, 6 and 8h arterial blood and at t = 8h cerebral cortex were sampled for determination of ammonia and amino acids. Control rats (NORM) were sampled without previous surgery. Repeated intragastric blood administration increased the already elevated arterial ammonia levels in PCS rats further. This resulted in higher cerebral cortex ammonia and glutamine levels after blood administration. Despite the accumulation of ammonia and glutamine, cerebral cortex glutamate concentrations remained unaltered. Yet, PCS rats became more encephalopathic after blood gavages, suggesting that there is not a clear-cut relation between cerebral cortex glutamate concentrations and degree of PSE. Interestingly, cerebral cortex concentrations of GABA, tyrosine and phenylalanine were markedly increased. Whether these observations are pathogenetically related to PSE remains to be established. The present model of simulated GI hemorrhage in PCS rats seems to be a suitable, clinically valid model for future research regarding hepatic encephalopathy.

Decreased plasma and tissue isoleucine levels after simulated gastrointestinal bleeding by blood gavages in chronic portacaval shunted rats

BACKGROUND

Previously, arterial concentrations of the essential branched chain amino acid isoleucine (Ile) were found to have decreased by more than 50% after gastrointestinal haemorrhage in patients and after intragastric blood administration in healthy humans and pigs. Hypothetically, this induced hypoisoleucinaemia could deplete tissue Ile pools.

AIMS

To study the effect of repeated blood gavages on arterial and tissue Ile levels during normal and impaired liver function.

SUBJECTS

Male Wistar rats.

METHODS

14 days after portacaval shunting or sham surgery, rats received 3 ml bovine erythrocytes or saline at 0, 1, 2, and 3 hours via a gastrostomy catheter in the duodenum. At 0, 2, 4, 6 and 8 hours arterial blood and at 8 hours intestine, liver, muscle, and cerebral cortex were sampled for determination of ammonia and amino acid concentrations.

RESULTS

In both groups repeated blood administration resulted in a marked decrease in plasma Ile (40-60%). This was accompanied by decreased tissue Ile concentrations in liver (50%), muscle (40-60%), and cerebral cortex (40-50%), but unaltered intestinal Ile levels. In contrast, the arterial and tissue concentrations of ammonia, urea, and of most amino acids increased, most strikingly of the other two branched chain amino acids, valine and leucine.

CONCLUSIONS

Simulated gastrointestinal bleeding by blood gavages in rats with and without impaired liver function leads to hypoisoleucinaemia and decreased tissue Ile pools.

Decreased plasma isoleucine concentrations after upper gastrointestinal haemorrhage in humans

BACKGROUND

A decrease in arterial isoleucine values after intragastric blood administration in pigs has been observed. This contrasted with increased values of most other amino acids, ammonia, and urea. After an isonitrogenous control meal in these pigs all amino acids including isoleucine increased, and urea increased to a lesser extent, suggesting a relation between the arterial isoleucine decrease and uraemia after gastrointestinal haemorrhage.

METHODS

To extend these findings to humans, plasma amino acids were determined after gastrointestinal haemorrhage in patients with peptic ulcers (n = 9) or oesophageal varices induced by liver cirrhosis (n = 4) and compared with preoperative patients (n = 106).

RESULTS

After gastrointestinal haemorrhage, isoleucine decreased in all patients by more than 60% and normalised within 48 hours. Most other amino acids increased and also normalised within 48 hours. Uraemia occurred in both groups, hyperammonaemia was seen in patients with liver cirrhosis.

CONCLUSIONS

These results confirm previous findings in animals and healthy volunteers that plasma isoleucine decreases after simulated upper gastrointestinal haemorrhage. This supports the hypothesis that the absence of isoleucine in blood protein causes decreased plasma isoleucine values after gastrointestinal haemorrhage, and may be a contributory factor to uraemia and hyperammonaemia in patients with normal and impaired liver function, respectively. Intravenous isoleucine administration after gastrointestinal haemorrhage could be beneficial and will be the subject of further research.

Prospective evaluation of faecal fatty acid excretion in short bowel syndrome in newborns

Short bowel syndrome (SBS) in the newborn results in limited intestinal absorptive capacity, leading especially to fatty acid (FA) malabsorption. It is unknown whether adaptation occurs in time in FA absorption, and whether this adaptation is chain-length dependent. The aid of the present study was to prospectively evaluate FA absorption and excretion during SBS in the newborn. Twenty-one neonates who underwent small bowel resection (of variable length) for various reasons (necrotizing enterocolitis, intestinal atresia, meconium peritonitis, cloacal extrophy, etc) were studied. Eight neonates had SBS, defined as a small bowel remnant of less than 50% of the original small bowel length related to gestational age. The mean remaining small bowel length in the SBS group was 34% (24% to 42%). The non-SBS control group consisted of 13 neonates who had only minor small bowel resections. The mean remaining bowel length for the non-SBS group was 95% (70% to 100%). The results show that the total fractional excretion of FA (FE-FA) at 2 weeks and 1, 2, 3, and 4 months postsurgery was 51% +/- 37%, 33% +/- 24%, 51% +/- 65%, 53% +/- 27%, and 7% +/- 2% in patients with SBS, versus 12% +/- 8%, 24% +/- 10%, 9% +/- 3%, 8% +/- 3% and 17% +/- 14% in the non-SBS controls, respectively (P < .05 by ANOVA). There appeared to be an amelioration in time in FA absorption, especially in the SBS group, after 3 months. FE-FA was chain-length related, being considerably less for C10 and C12 than for C14 and longer amounts. An amelioration of absorption occurred in the SBS patients, especially with the longer-chain FA. On the basis of the study data, the authors conclude that in the initial adaptation phase shorter chain lengths are better absorbed than longer chain lengths; however, in the latter FA group, substantial adaptation occurs with time.

Supplementation of enteral nutrition with butyrate leads to increased portal efflux of amino acids in growing pigs with short bowel syndrome

Previously, short-chain fatty acids (SCFAs) infused into the hindgut or administered intravenously have been shown to stimulate intestinal adaptation after massive small bowel resection. To study the effects of enterally supplemented n-butyrate on food digestion and absorption in growing pigs with short bowel syndrome, the authors examined the portal efflux of glucose and amino acids during a meal. In 12 growing pigs, 75% of the small intestine was resected. Five control (CONT) animals underwent transection and reanastomosis of the small bowel. A splenic vein, the aorta, the portal vein, and the stomach were catheterized. Postoperatively, seven enterectomized (ENT) pigs and the CONT pigs were fed by infusion of a liquid diet, without SCFAs, through the gastrostomy catheter. Five enterectomized animals received the same diet, supplemented with butyrate (ENTB) (0.26 g/kg body weight/d). After 3 weeks, the portal efflux of amino acids and glucose was measured after 2 hours of constant feeding. The portal efflux of glucose expressed per kilogram of body weight in the ENT group was 10% of that in the CONT group, and in the ENTB group it was 42%. No significant difference in portal glucose efflux between the ENT and the ENTB groups was found. The portal efflux of amino acids during a meal in the ENT group in relation to the CONT groups was 34%; in the ENTB group it was 63%. These data suggest that enteral supplementation with SCFAs leads to improvement of intestinal food digestion and absorption during short bowel syndrome, possibly related to improved intestinal adaptation.

Ammonia and glutamine metabolism during liver insufficiency: the role of kidney and brain in interorgan nitrogen exchange

BACKGROUND

During liver failure, urea synthesis capacity is impaired. In this situation the most important alternative pathway for ammonia detoxification is the formation of glutamine from ammonia and glutamate. Information is lacking about the quantitative and qualitative role of kidney and brain in ammonia detoxification during liver failure.

METHODS

This review is based on own experiments considered against literature data.

RESULTS AND CONCLUSIONS

Brain detoxifies ammonia during liver failure by ammonia uptake from the blood, glutamine synthesis and subsequent glutamine release into the blood. Although quantitatively unimportant, this may be qualitatively important, because it may influence metabolic and/or neurotransmitter glutamate concentrations. The kidney plays an important role in adaptation to hyperammonaemia by reversing the ratio of ammonia excreted in the urine versus ammonia released into the blood from 0.5 to 2. Thus, the kidney changes into an organ that netto removes ammonia from the body as opposed to the normal situation in which it adds ammonia to the body pools.

Influence of storage conditions on normal plasma amino-acid concentrations

Conflicting information in the literature is given concerning the optimal preparation and storage conditions of plasma samples for amino-acid analysis. To assess the optimal pre-storage treatment, we compared several methods and studied their influence on plasma amino-acid levels of rats and humans, stored at different temperatures. In rat plasma, the frequently reported degradation of glutamine was not measurable at a storage temperature of -70 degrees C. However, storage of native, not deproteinised plasma at this temperature, resulted in a 32% decrease of arginine and a 30% increase in ornithine after 24 weeks. Deproteinisation prohibited this arginine decay. At -20 degrees C, arginine decay was even more pronounced, whereas glutamine decreased by 14% in untreated plasma, by 10% in sulfosalicylic acid deproteinised plasma and by 3% if the deproteinisation was followed by removal of the protein pellet and subsequent neutralisation. To confirm these unexpected results in humans, we repeated this experiment with plasma of 6 volunteers. In contrast to rat plasma, we did not observe any changes in arginine and ornithine concentrations in human plasma stored at -70 degrees C. At -20 degrees C the reduction in glutamine was only 4-5%. These results suggest that interspecies differences in enxymatic activity exist in plasma. Finally, having assessed the optimal treatment and storage conditions (deproteinisation followed by storage at -70 degrees C), samples were obtained from a total of 112 human volunteers, stratified for age and sex, and amino-acids were measured. In the female group, we found a tendency to a gradual increase in most amino-acid concentrations with advancing age, which however only reached significance for histidine, citrulline, alanine and leucine. These observations demonstrate that plasma samples for amino-acid analysis should be deproteinised and stored at -70 degrees C. Also important interspecies differences appear to exist in plasma enzymatic activity. Finally, control samples should be taken from an age and sex matched control group.

Muscle ammonia and glutamine exchange during chronic liver insufficiency in the rat

The aim of this study was to investigate the role of skeletal muscle in ammonia and glutamine metabolism during chronic hyperammonemia induced by liver insufficiency. The hindquarter ammonia and amino acid fluxes and muscle tissue concentrations were studied in two rat models of chronic liver insufficiency, portacaval shunting and portacaval shunting plus bile-duct ligation, as well as in sham-operated animals, 7 and 14 days after surgery, and in normal, unoperated rats. To reduce nutritional influences, portacaval-shunted rats and sham-operated rats were pair-fed to portacaval shunt biliary obstruction rats. Arterial ammonia levels were elevated in both liver insufficiency groups. In the portacaval shunting plus bile-duct ligation group, arterial glutamine levels were elevated compared with sham-operated controls. No net hind-quarter ammonia uptake was observed in any of the groups, despite hyperammonemia in the chronic liver insufficiency groups. Hindquarter glutamine release was always increased in the liver insufficiency groups compared with sham-operated controls, despite similar muscle glutamine levels in the sham-operated and hyperammonemic groups, suggesting enhanced muscle glutamine synthesis in the latter groups. Muscle ammonia levels were always increased and muscle glutamate decreased in the hyperammonemic groups, probably indicating glutamate consumption by enhanced glutamine synthesis. The increased phenylalanine tissue concentrations and efflux in portacaval shunt/biliary obstruction rats suggest that enhanced net muscle protein breakdown, amino acid catabolism and transamination, rather than ammonia uptake from the blood furnish amino acids and ammonia for enhanced glutamine synthesis. These experiments suggest that nutritional factors are important in explaining altered muscle metabolism during chronic liver insufficiency.

Effects of methionine sulphoximine treatment on renal amino acid and ammonia metabolism in rats

Renal glutamine metabolism in relation to ammoniagenesis has been extensively studied during chronic metabolic acidosis, when arterial glutamine levels are reduced. However, little is known about the effects of reduced glutamine delivery on renal glutamine and ammonia metabolism at physiological systemic pH values. Therefore, a model of decreased arterial glutamine concentrations at normal pH values was developed using methionine sulphoximine (MSO). Renal glutamine and ammonia metabolism was measured by determining fluxes and intracellular concentrations after an overnight fast in ether anaesthetized normal rats, MSO-treated rats and their pair-fed controls. Moreover, fluxes and intracellular concentrations of several other amino acids were determined concomitantly. After 2 and 4 days of MSO treatment, arterial glutamine concentrations were reduced to 55%, while arterial ammonia concentrations increased by 70%. Kidney glutamine uptake reduced, but systemic pH was unchanged. Fractional extraction of glutamine remained unchanged, suggesting that also in vivo net uptake of glutamine by the kidney at subnormal levels is related to arterial glutamine concentrations. As a result, at day 2 but not at day 4, the kidney reduced the net release of ammonia into the renal vein and thus reduced net renal ammonia addition to body ammonia pools. Therefore at day 2, the kidney seems to play an important role in adaptation to both hyperammonaemia and hypoglutaminaemia.

Renal ammonia and glutamine metabolism during liver insufficiency-induced hyperammonemia in the rat

Renal glutamine uptake and subsequent urinary ammonia excretion could be an important alternative pathway of ammonia disposal from the body during liver failure (diminished urea synthesis), but this pathway has received little attention. Therefore, we investigated renal glutamine and ammonia metabolism in midly hyperammonemic, portacaval shunted rats and severely hyperammonemic rats with acute liver ischemia compared to their respective controls, to investigate whether renal ammonia disposal from the body is enhanced during hyperammonemia and to explore the limits of the pathway. Renal fluxes, urinary excretion, and renal tissue concentrations of amino acids and ammonia were measured 24 h after portacaval shunting, and 2, 4, and 6 h after liver ischemia induction and in the appropriate controls. Arterial ammonia increased to 247 +/- 22 microM after portacaval shunting compared to controls (51 +/- 8 microM) (P < 0.001) and increased to 934 +/- 54 microM during liver ischemia (P < 0.001). Arterial glutamine increased to 697 +/- 93 microM after portacaval shunting compared to controls (513 +/- 40 microM) (P < 0.01) and further increased to 3781 +/- 248 microM during liver ischemia (P < 0.001). In contrast to controls, in portacaval shunted rats the kidney net disposed ammonia from the body by diminishing renal venous ammonia release (from 267 +/- 33 to -49 +/- 59 nmol/100 g body wt per min) and enhancing urinary ammonia excretion from 113 +/- 24 to 305 +/- 52 nmol/100 g body wt per min (both P < 0.01). Renal glutamine uptake diminished in portacaval shunted rats compared to controls (-107 +/- 33 vs. -322 +/- 41 nmol/100 g body wt per min) (P < 0.01). However, during liver ischemia, net renal ammonia disposal from the body did not further increase (294 +/- 88 vs. 144 +/- 101 nmol/100 g body wt per min during portacaval shunting versus liver ischemia). Renal glutamine uptake was comparable in both hyperammonemic models. These results indicate that the rat kidney plays an important role in ammonia disposal during mild hyperammonemia. However, during severe liver insufficiency induced-hyperammonemia, ammonia disposal capacity appears to be exceeded.

Metabolic adaptation of the kidney to hyperammonemia during chronic liver insufficiency in the rat

The aim of this study was to evaluate the role of renal ammonia and glutamine metabolism in the metabolic adaptation to chronic liver insufficiency-induced hyperammonemia in the rat. To this purpose, urinary excretion, renal net exchange and tissue concentrations of ammonia and amino acids were measured in anesthetized, normal control rats that did not undergo surgery, in control rats that underwent sham surgery, in rats that underwent portacaval shunting and in rats that underwent both portacaval shunting and bile duct ligation. Rats that underwent sham surgery and portacaval shunting were pair-fed with rats that underwent portacaval shunting and biliary obstruction, to correct for anorexia in that group, and all rats that were operated on were studied 7 and 14 days after surgery. Arterial ammonia and glutamine levels were elevated in groups that underwent portacaval shunting and portacaval shunting plus biliary obstruction at all time points. At days 7 and 14, total renal ammonia production decreased in rats that underwent portacaval shunting and in rats that underwent portacaval shunting plus biliary obstruction, associated with a 50% decrease in net renal glutamine uptake and strongly diminished net ammonia release into the renal vein, which was most prominent in the group that underwent portacaval shunting plus biliary obstruction. Urinary ammonia excretion was similar in rats that underwent portacaval shunting and in those that underwent sham surgery but was increased more than 200% at days 7 and 14 in rats that underwent portacaval shunting plus biliary obstruction. In this group, in contrast to portacaval-shunted rats, the kidney appeared to be an organ of net ammonia disposal from the body. In separate experiments in unanesthetized, unrestrained rats, similar changes in urinary ammonia excretion were observed without changes in arterial pH, excluding an effect of anesthesia or pH on the obtained results. These results indicate that the kidney plays an important role in the metabolic adaptation to hyperammonemia during chronic liver insufficiency in the rat.

Intestinal glutamine and ammonia metabolism during chronic hyperammonaemia induced by liver insufficiency

During liver insufficiency, besides portasystemic shunting, high arterial glutamine concentrations could enhance intestinal glutamine consumption and ammonia generation, thereby aggravating hyperammonaemia. To investigate this hypothesis, portal drained viscera (intestines) fluxes and jejunal tissue concentrations of ammonia and glutamine were measured in portacaval shunted rats with a ligated bile duct, portacaval shunted, and sham operated rats, seven and 14 days after surgery, and in normal unoperated controls. Effects of differences in food intake were minimised by pair feeding portacaval shunted and sham operated with portacaval shunted rats with biliary obstruction. At both time points, arterial ammonia was increased in the groups with liver insufficiency. Also, arterial glutamine concentration was raised in all operated groups compared with normal unoperated controls. At both time points, ammonia production by portal drained viscera was reduced in portacaval shunted rats with biliary obstruction, portacaval shunted, and sham operated rats compared with normal unoperated controls, and no major differences were found between these operated groups. At day 7 in all operated groups glutamine uptake by portal drained viscera was lower than in normal unoperated controls, but no major differences were found at day 14. These experiments show that ammonia generation by portal drained viscera remains unchanged in rats with chronic liver insufficiency despite alterations in arterial glutamine concentrations and intestinal glutamine uptake. The hyperammonaemia seems to be mainly determined by the portasystemic shunting.

Cerebral cortex ammonia and glutamine metabolism in two rat models of chronic liver insufficiency-induced hyperammonemia: influence of pair-feeding

Enhanced cerebral cortex ammonia uptake, subsequent glutamine synthesis, and glutamine release into the bloodstream have been hypothesized to deplete cerebral cortex glutamate pools. We investigated this hypothesis in rats with chronic liver insufficiency-induced hyperammonemia and in pair-fed controls to rule out effects of differences in food intake. Cerebral cortex plasma flow and venous-arterial concentration differences of ammonia and amino acids, as well as cerebral cortex tissue concentrations, were studied 7 and 14 days after surgery in portacaval-shunted/bile duct-ligated, portacaval-shunted, and sham-operated rats, while the latter two were pair-fed to the first group, and in normal unoperated ad libitum-fed control rats. At both time points, arterial ammonia was elevated in the chronic liver insufficiency groups and arterial glutamine was elevated in portacaval shunt/biliary obstruction rats compared to the other groups. In the chronic liver insufficiency groups net cerebral cortex ammonia uptake was observed at both time points and was accompanied by net glutamine release. Also in these groups, cerebral cortex tissue glutamine, many other amino acid, and ammonia levels were elevated. Tissue glutamate levels were decreased to a similar level in all operated groups compared with normal unoperated rats, irrespective of plasma and tissue ammonia and glutamine levels. These results demonstrate that during chronic liver insufficiency-induced hyperammonemia, the rat cerebral cortex enhances net ammonia uptake and glutamine release. However, the decrease in tissue glutamate concentrations in these chronic liver insufficiency models seems to be related primarily to nutritional status and/or surgical trauma.

Partial enterectomy in the rat does not diminish muscle glutamine production

The hypothesis was posed that consumption of the amino acid glutamine by the splanchnic tissues is an important regulating mechanism for its production in muscle. Therefore, glutamine consumption or production in portal-drained viscera (PDV), liver, and hindquarter was measured by determining fluxes and intracellular concentrations after 80% enterectomy or SHAM operation in rats. Moreover, fluxes and intracellular concentrations of several other amino acids, ammonia, and liver urea production were determined concomitantly. After enterectomy, arterial glutamine concentration was increased, PDV glutamine consumption was decreased by 77%, and liver glutamine consumption was unchanged compared with values in SHAM-operated rats. Although hindquarter glutamine production remained unchanged after enterectomy, intracellular glutamate concentration (glutamine precursor) was lower, suggesting that enterectomy induces changes in muscle metabolism without changing the flux of glutamine. For the remaining gut, it was calculated that after enterectomy glutamine consumption per gram remaining gut tissue increased. These results cast doubt on the hypothesis that diminished splanchnic glutamine uptake can reduce muscle glutamine production.

Cerebral cortex ammonia and glutamine metabolism during liver insufficiency-induced hyperammonemia in the rat

Hyperammonemia has been suggested to induce enhanced cerebral cortex ammonia uptake, subsequent glutamine synthesis and accumulation, and finally net glutamine release into the blood stream, but this has never been confirmed in liver insufficiency models. Therefore, cerebral cortex ammonia- and glutamine-related metabolism was studied during liver insufficiency-induced hyperammonemia by measuring plasma flow and venous-arterial concentration differences of ammonia and amino acids across the cerebral cortex (enabling estimation of net metabolite exchange), 1 day after portacaval shunting and 2, 4, and 6 h after hepatic artery ligation (or in controls). The intra-organ effects were investigated by measuring cerebral cortex tissue ammonia and amino acids 6 h after liver ischemia induction or in controls. Arterial ammonia and glutamine increased in portacaval-shunted rats versus controls, and further increased during liver ischemia. Cerebral cortex net ammonia uptake, observed in portacaval-shunted rats, increased progressively during liver ischemia, but net glutamine release was only observed after 6 h of liver ischemia. Cerebral cortex tissue glutamine, gamma-aminobutyric acid, most other amino acids, and ammonia levels were increased during liver ischemia. Glutamate was equally decreased in portacaval-shunted and liver-ischemia rats. The observed net cerebral cortex ammonia uptake, cerebral cortex tissue ammonia and glutamine accumulation, and finally glutamine release into the blood suggest that the rat cerebral cortex initially contributes to net ammonia removal from the blood during liver insufficiency-induced hyperammonemia by augmenting tissue glutamine and ammonia pools, and later by net glutamine release into the blood. The changes in cerebral cortex glutamate and gamma-aminobutyric acid could be related to altered ammonia metabolism.

A simple new method for repeated in vivo cerebral cortex flux measurement in rats

A new application of an indicator dilution technique, using nonradioactive para-aminohippuric acid, is described for superior sagittal sinus blood flow determination in rats. Superior sagittal sinus blood flow, mainly representing cerebral cortex blood flow, amounted to 541 +/- 49 microliters/min in ketamine-anesthetized, but otherwise normal, rats breathing room air. Increasing arterial pCO2 enhanced superior sagittal sinus blood flow (P less than 0.01), providing evidence that this method correctly measures cerebral blood flow. The respiratory quotient was 1.1 and the cerebral cortex metabolic rate of oxygen consumption was +/- 1.45 mumol/min. Cerebral cortex ammonia uptake was not significantly different from zero and of the amino acid fluxes, only alanine differed from zero (P less than 0.05). Flux measurements are crucial in studies of healthy or altered organ metabolism in both experimental animals and postoperative surgical patients. We devised a simple and economical method of repeated cerebral cortex flux measurement in rats that is a potentially valuable tool in metabolic studies of the cerebral cortex.

Altered glutamine metabolism in rat portal drained viscera and hindquarter during hyperammonemia

In normal rats, muscle is the major glutamine releasing organ and gut is the major glutamine consuming organ. It has been suggested that enhanced muscle ammonia detoxification and gut ammonia production occurs during liver insufficiency-induced hyperammonemia. Therefore, ammonia and amino acid fluxes across portal-drained viscera and hindquarter, and muscle concentrations were measured in portacaval shunted and acute liver ischemia rats. Arterial ammonia and most amino acids were increased after portacaval shunting and increased progressively during liver ischemia, but net hindquarter ammonia uptake was not observed. Net hindquarter glutamine efflux was increased during portacaval shunting, but it decreased during liver ischemia, while muscle glutamine concentrations increased. The comparable net portal drained viscera glutamine uptake in normal and portacaval shunted rats changed during liver ischemia from net uptake to release, coinciding with release of most other amino acids. These results cast doubt on the ammonia detoxifying role of muscle during acute liver ischemia-induced hyperammonemia in the rat. The portal drained viscera glutamine release during severe hyperammonemia could be due to intestinal damage.