Effects of amino acid infusions on liver regeneration after partial hepatectomy in the rat

Administration of solutions high in branched-chain amino acids (BCAA) has been advocated in patients with severe liver failure; however, the effect of this treatment on the process of liver regeneration is still unclear. In the present study using rats we investigated the influence on liver regeneration of infusing solutions differing in amino acid content. After 75% hepatectomy, rats were infused via jugular vein with one of the following solutions: Sol A) 10% dextrose, Sol B) 10% dextrose + 3% amino acids (22% BCAA), Sol C) 10% dextrose + 3% amino acids (35% BCAA). Liver regeneration was estimated by measuring the incorporation of 3H-thymidine into DNA at five different time points after the operation. Peak regeneration occurred earlier in rats infused with the BCAA-enriched solution compared to animals infused with the standard amino acid solution or with dextrose alone. The increased incorporation of 3H-thymidine into DNA at 24 hr in rats infused with the BCAA-enriched solution was associated with elevated plasma levels of BCAA and decreased concentrations of tyrosine, phenylalanine, and methionine in comparison with the other two treatment groups. These results suggest that liver regeneration in rats can be accelerated by administering a parenteral nutrition solution tailored to normalize the deranged pattern of plasma amino acids associated with compromised liver function.

Increased incidence of renal allograft thrombosis under cyclosporine immunosuppression

Six of 325 patients undergoing renal transplantation under combined cyclosporine (CsA)-prednisone immunosuppression displayed renal artery thrombosis between 4 and 12 days after transplantation. All six patients had satisfactory initial revascularization, as ascertained by radionuclide scan and renal function. In none was the thrombosis considered to be secondary to rejection, either by clinical course or upon renal biopsy. Since there was no clear etiologic factor and since none of the overlapping 297 patients treated with azathioprine-prednisone displayed this complication, these cases appear to support the hypothesis that CsA alters intravascular hemostatic homeostasis. Data in experimental models are consistent with a predisposing factor to thrombosis, namely CsA reduces the synthesis of prostacyclin stimulating factors, leading to decreased prostacyclin production by vascular endothelial cells, and to failure to inhibit platelet aggregation.

Infusion of branched-chain amino acids and ammonium salts in rats with portacaval shunts

During infusion into rats with a portacaval shunt of either ammonium (NH4+) salts alone or NH4+ salts combined with the three branched-chain amino acids (BCAAs) in equimolar quantities, we assessed neurologic function and measured plasma and brain ammonia and amino acid levels and the brain content of amine neurotransmitters and their metabolites. Survival was lengthened and neurologic function was preserved longer in rats receiving BCAAs. Infusion of BCAAs resulted in lower plasma and brain ammonia concentrations compared with rats receiving NH4+ salts alone. Plasma glutamine and alanine levels were higher in rats receiving BCAAs, suggesting increased ammonia detoxification. Loss of neurologic function, regardless of which solution was infused, eventually occurred and corresponded with decreased brain norepinephrine and increased brain alanine levels. These results suggest that BCAAs can protect against hyperammonemia by stimulating the peripheral detoxification of ammonia.

Effect of hyperammonemia and methionine sulfoximine on the kinetic parameters of blood-brain transport of leucine and phenylalanine

The activity of the blood-brain neutral amino acid transport system is increased in rats infused with ammonium salts or rendered hyperammonemic by a portacaval anastomosis. This effect may be due to a direct action of ammonia or to some metabolic consequence of high ammonia levels, such as increased brain glutamine synthesis. To test these possibilities we evaluated the kinetic parameters of blood-brain transport of leucine and phenylalanine in control rats, in rats after continuous 24 h infusion of ammonium salts (NH4+ = 2.5 mmol X kg-1 X h-1), and in rats treated with methionine sulfoximine, an inhibitor of glutamine synthetase, before infusion of ammonium salts. In ammonia-infused rats without methionine sulfoximine treatment, the KD and Vmax of phenylalanine transport were increased, respectively, about 170% and 80% compared to controls, whereas the Km and Vmax of leucine transport were increased, respectively, about 100% and 200%. Electron microscopy demonstrated marked swelling of astrocytic processes around brain capillaries of ammonia-infused rats; however, capillary permeability to horseradish peroxidase apparently was not increased by ammonia infusion. Administration of methionine sulfoximine before ammonia infusion inhibited glutamine synthesis and prevented the changes in transport of leucine and phenylalanine, but apparently did not reverse the perivascular swelling. These results suggest that the ammonia-induced increase in the activity of transport of large neutral amino acids across the blood-brain barrier requires glutamine synthesis in brain, and is not a direct effect of ammonia.

Methionine sulfoximine prevents the accumulation of large neutral amino acids in brain of portacaval-shunted rats

Portal-systemic shunting and hyperammonemia lead to an accumulation of the large neutral amino acids in brain and apparently alter transport of neutral amino acids across the blood-brain barrier. It has been proposed that portal-systemic shunting leads to a high brain concentration of glutamine, a product of cerebral ammonia detoxification, and thereby affects the transport of other neutral amino acids across the blood-brain barrier. To test this hypothesis, rats with a portacaval shunt were treated with L-methionine-dl-sulfoximine (MSO), an inhibitor of glutamine synthesis. Treatment with MSO resulted in lower concentrations of the neutral amino acids in brain of portacaval-shunted rats and a higher brain ammonia concentration, compared with untreated shunted rats. These results suggest that the accumulation of neutral amino acids in brain after portacaval shunt depends on the increased synthesis of glutamine in brain.

Are urinary enzymes useful markers of kidney damage in obstructive jaundice? An experimental study on Sprague-Dawley rats

To evaluate the reliability of urinary enzymes as markers of renal tubular damage in obstructive jaundice, research was carried out on 26 Sprague-Dawley rats submitted to bile duct ligation and on 16 sham-operated rats. The fractional clearances of lysozyme (CfrLYS) and of malto-dehydrogenase (CfrMDH)-indices of tubular function-and the fractional excretions of gamma-glutamyltransferase (UfrGGT) and of alpha-glucosidase (UfrAGL)-indices of tubular anatomic damage - were measured 5, 10, 20 and 30 days after operation. Creatinine clearance, urinary sodium excretion, urinary potassium excretion, proteinuria, plasma bilirubin and bile acids were also measured. Kidneys were taken for histology. All rats submitted to common bile duct ligation had high levels of bilirubin and bile acids; proximal tubules were damaged and the extent of the lesions increased with time. However, creatinine clearance, urinary sodium excretion, proteinuria, CfrMDH and UfrAGL gave no indication of renal lesions, whereas CfrLYS and UfrGGT were significantly higher 20 and 30 days after bile duct ligation, respectively. These findings show that CfrLYS and UfrGGT could be useful tests for renal tubular lesions in jaundice.

Methionine sulfoximine prevents the accumulation of large neutral amino acids in brain of hyperammonemic rats

Accumulation of neutral amino acids in the brain due to altered transport across the blood-brain barrier appears to be a consequence of portal-systemic shunting and hyperammonemia. It has been suggested that high brain concentrations of glutamine, a product of cerebral ammonia detoxification, accelerates the transport of other neutral amino acids from blood to brain. To test this hypothesis, normal rats were infused with ammonium salts with or without pretreatment with L-methionine-dl-sulfoximine (MSO), an inhibitor of glutamine synthesis. Pretreatment with MSO prevented most ammonium salt-induced changes in the concentrations of the neutral amino acids in brain, suggesting that hyperammonemia alters the transport of neutral amino acids across the blood-brain barrier by causing the brain glutamine level to rise.

Cerebral amino acid levels and transport after portocaval shunt in the rat: effects of liver arterialization

Altered plasmatic and cerebral amino acid patterns have been observed after portocaval shunt in the rat. Similar alterations have been found in plasma and in cerebrospinal fluid of cirrhotic patients and are likely to play an important role in the pathogenesis of hepatic encephalopathy. Impaired liver blood flow could contribute to these biochemical abnormalities. Therefore we wondered whether liver arterialization, by improving liver perfusion, could have any beneficial effects on the altered amino acid levels occurring in the rat after portocaval shunt. Amino acid concentrations were determined in four cerebral regions and in the plasma of shunted rats with or without liver arterialization, 4 weeks after surgery. Blood-brain barrier transport was studied with the Oldendorf's technique. After portocaval shunt, we observed lower plasma levels of the branched chain amino acids valine, isoleucine, leucine, and net higher levels of the aromatic tyrosine and phenylalanine and of glutamine. In the cerebral regions, we observed a slight increase of branched chain amino acids and an enormous increase of tyrosine, phenylalanine, tryptophan, histidine, and glutamine. Arterialization of the liver made no difference to the postportocaval shunt plasma levels of branched chain amino acids, while it almost normalized those of aromatics. In the cerebral regions, we observed a marked improvement in the level of tyrosine, phenylalanine, tryptophan, and histidine. The enhancement of blood-brain barrier transport for the neutral amino acid class, observed after portocaval shunt, was not influenced by liver arterialization. We conclude that, in our model, liver arterialization improves the pathologic amino acid levels following portocaval shunt. This would be in agreement with clinical reports suggesting that hepatic encephalopathy is less frequent after portocaval shunt when associated with arterialization of the liver.

Effect of L-dopa treatment on cerebral amino acid levels in rats after portocaval anastomosis

L-Dopa therapy has been suggested as effective in the reversal of hepatic coma both in humans and in animals. Beneficial effects have been reported also in chronic hepatic encephalopathy. There are many possible mechanisms through which L-dopa could ameliorate this pathological state. The present study was carried out to clarify whether the L-dopa effect could be mediated through an improvement of the brain neutral amino acid patterns, since it competes for the same transport carrier at the blood-brain barrier. A first group of rats was orally administered L-dopa (10 mg/100 g body weight daily) for 1 month following portocaval anastomosis. A second group was intraperitoneally injected (1.5 mg/100 g body weight daily) for 1 week, a month after portocaval shunt. Amino acid levels were determined in plasma and in four cerebral regions. No beneficial effects were observed clinically (in general condition, body weight, or hypertonic posture) in rats receiving L-dopa compared to controls. The large increase of tyrosine, phenylalanine, tryptophan, histidine, and glutamine that occurs in the cerebral tissue after portocaval shunt was also not affected by L-dopa administration. In conclusion, in this experimental condition we had no clinical improvement in shunted animals receiving L-dopa. Moreover, this compound did not seem to influence the pathological increase of aromatic amino acids in the brain, which is considered to play an important role in hepatic encephalopathy.

Does liver arterialization improve the altered cerebral amino acid pattern in the rat after portacaval shunt?

Altered plasma and brain amino acid patterns have been observed in the rat after portacaval shunt. Similar alterations are likely to play an important role in hepatic encephalopathy in humans. In our model, liver arterialization remarkably improves the pathologic amino acid levels following portacaval shunt.

Cerebral amino acid levels and uptake in rats after portocaval anastomosis: I. Regional studies in vitro

Uptake of various amino acids was studied in slices from brain regions of rats four weeks after portocaval anastomosis. No differences of the inulin compartment were observed between control and experimental animals. After 60-minutes incubation, uptake showed an overall pattern of diminution. This was more evident for some amino acids: valine, methionine, and lysine exhibited a lowering of about 30%, which was fairly uniform in the four tested regions; others showed a regional decrease-- alanine in pons-medulla, phenylalanine in cerebellum, histidine and GABA in mesodiencephalon. This decrease did not seen to be related to transport classes. The restricted entry of amino acids into brain cells in portocaval encephalopathy is somewhat difficult to explain; a decreased rate of protein synthesis may be of some importance, but other factors, such as a "carrier" impairment, effects on release and on amino acid metabolism, may also be involved.

Cerebral amino acid levels and uptake in rats after portocaval anastomosis: II. Regional studies in vivo

Amino acid levels have been determined in plasma and in four cerebral regions of rats one month after portocaval shunt. Many plasma amino acids are significantly lowered (asparagine, glutamine, theonine, serine, alanine, valine, leucine, isoleucine, cystine, lysine), while others remain unchanged (taurine, glycine, proline, tryptophan, ornithine, histidine, arginine). Asparagine and glutamine levels are significantly higher than in normal rats, and a net increase of tyrosine (100%), phenylalanine (50%) and citrulline (50%) is evident. In the shunted rat brain the most prominent feature is a very large rise (up to fivefold) of tyrosine, phenylalanine, histidine, citrulline, tryptophan, and glutamine uniformly in the tested regions. Other neutral amino acids are slightly increased. Lysine and arginine are decreased in cerebellum and pons-medulla; taurine, in forebrain and cerebellum. Cerebral permeability to L-amino acids was studied in vivo. Neutral amino acid permeability is greatly increased, whereas basic amino acids show a net decrease in their rate of passage from blood to the brain. No changes are observed for GABA and glutamic acid. These data suggest an altered permeability of the cerebral capillary membranes, which seems to be selective for the different amino acid transport classes. Competitive inhibition experiments demonstrated that the increased brain permeability to neutral amino acids after portocaval shunt is due to an enhancement of the saturable transport. The sharp rise in the brain of some essential neutral amino acids (phenylalanine, tyrosine, trytophan, histidine), largely exceeding their changes in plasma, and the slight cerebral increase of other neutral amino acids despite their lowered level and the rise of competing amino acids in the plasma, is consistent with our observation of enhanced transport for the neutral class. In hepatic encephalopathy, correction of the altered plasma amino acid levels has been reported to improve the clinical status. If this result is connected to the concomitant correction of the brain amino acid levels, carefully selected competitive inhibition among various plasma amino acids could be a useful therapeutic tool in this pathologic condition. However, the increased activity of the neutral amino acid transport system adds a new factor to the problem, since it probably implies that the competing amino acids will accumulate to unphysiological levels in the brain.

[Aromatic and branched chain amino acids after porto-caval anastomosis: plasma and brain regional levels in the rat (author's transl)]

Automated analysis of aromatic and branched chain amino acids was performed in plasma and in four cerebral regions of rats submitted to chronic porto-caval shunt. Compared to controls, plasma of the operated animals exhibited a significant diminution of valine, leucine, isoleucine, a net increase of phenylalanine and tyrosine, with unchanged tryptophan levels. Brain valine, leucine and isoleucine were either increased or unchanged, whereas an enormous increase of aromatic amino acids, uniform in the four cerebral regions, was observed. The lack of correlation between plasmatic and cerebral levels of these essential amino acids leads to the hypothesis that cerebral permeability to amino acids is modified after experimental portocaval anatomosis: we recent confirmed that blood-brain mediated transport of the neutral amino acids is increased in this condition. A slower cerebral turnover of these metabolites could also contribute to elevate their cerebral concentrations after portocaval shunt.

[In vivo aminoacid transport in the brain of the rat with porto-caval anastomosis (author's transl)]

Cerebral capillary permeability to L-amino acids was studied in rats submitted to porto-caval anastomosis 4 weeks before. The short-term intracarotidal injection technique described by Oldendorf was used throughout. Neutral amino acid permeability appeared to be greatly increased, the most important enhancement being for the tryptophan. On the opposite, basic amino acids showed a net decrease in their rate of passage from blood to the brain. No changes were observed for GABA and glutamic acid. These data suggest a marked modification of the permeability of the cerebral capillary membranes in the rat with chronic portocaval anastomosis. Moreover, such alterations are selective for the different amino acid transport classes. Competitive inhibition decreased the permeability of methionine at the same level in both control and experimental animals: therefore, the neutral amino acid increased entry into the rat brain after porto-caval shunt is due to an enhancement of the transport processes.

Investigations on the turnover of adrenocortical mitochondria. IV. A stereological study of the effect of chronic treatment with ACTH on the size and number of rat zona reticularis mitochondria

The effects of chronic administration of of ACTH (up to 36 consecutive days) on the mitochondria of the zona reticularis of the rat adrenal cortex were investigated by stereologic techniques. It was found that ACTH induces two phases of hypertrophy of mitochondria alternating with two proliferative stages, which are associated with a significant decrease in the average volume of the organelles. It is suggested that, as in the zona fasciculata, ACTH controls the processes of growth and division of mitochondria in the zona reticularis. The mechanism underlying this action of ACTH as well as the differences between the responses to ACTH of the mitochondrial population of the two adrenal zones are discussed in the light of evidence indicating that mitochondria contain a complete genetic apparatus largely independent of nuclear control.

Effect of ACTH on the zona reticularis of the rat adrenal cortex: an ultrastructural stereologic study

The effects of ACTH on the rat adrenal zona reticularis were investigated by stereologic methods. It was found that the zona reticularis cell responsiveness to ACTH is similar to that of the zona fasciculata elements. This excludes that the zona reticularis of the adult rat can only function as the site of destruction of worn-out elements migrating from the adrenal outer zones.