Hepatic amino nitrogen conversion and organ N-contents in hypothyroidism, with thyroxine replacement, and in hyperthyroid rats

Prednisolone but not infliximab aggravates the upregulated hepatic nitrogen elimination in patients with active inflammatory bowel disease

BACKGROUND

Catabolism and weight loss are serious problems in patients with active inflammatory bowel disease (IBD). The body nitrogen (N) depletion is partly related to increased hepatic capacity for the elimination of N through urea synthesis. This is probably caused by the inflammation per se, and the treatment with prednisolone may aggravate the problem, whereas the effect of biological therapy is unknown. Therefore, we examined the effects of prednisolone or infliximab on the regulation of urea synthesis in patients with active IBD.

METHODS

Urea synthesis was quantified by the functional hepatic nitrogen clearance (FHNC), i.e., the slope of the linear relationship between the urea nitrogen synthesis rate and the blood α-amino nitrogen concentration during alanine infusion. Thirty-seven patients with active IBD treated with either prednisolone or infliximab were examined before and after 7 days of treatment.

RESULTS

At baseline, the FHNC was similar in the 2 treatment groups (36 L/h). After 7 days, prednisolone increased the FHNC by 40% (55 L/h) (P = 0.03), whereas infliximab tended to reduce the FHNC by 15% (30 L/h) (P = 0.09). The changes in the FHNC differed significantly between the 2 treatment groups (P < 0.01).

CONCLUSIONS

Prednisolone treatment further upregulated urea synthesis, which increases the hepatic loss of nitrogen and promotes body catabolism. In contrast, infliximab treatment caused no such aggravation and likely reduced the N loss. These results may argue in favor of infliximab therapy for IBD and add to the pathophysiological understanding of the interplay between inflammation, catabolism, and anti-inflammatory treatment.

Thyroid hormone as a determinant of metabolic and contractile phenotype of skeletal muscle

Skeletal muscles are composed of several types of fibers with different contractile and metabolic properties. Genetic background and type of innervation of the fibers primarily determine these properties, but thyroid hormone (TH) is a powerful modulator of the fiber phenotype. The rates of contraction and relaxation are stimulated by TH, as are the energy consumption and heat production associated with activity. Quantitative and qualitative changes in substrate metabolism accommodate the increase in ATP turnover. Because of the total mass of skeletal muscle, these changes affect whole-body physiology. Although apparently straightforward, the phenotypic shifts induced by TH are highly complex and fiber specific. This review addresses the mechanisms by which TH may modulate fiber gene expression and discusses some of the implications of the TH-regulated changes in metabolic and contractile phenotype of skeletal muscle.

Cirrhosis and endotoxin decrease urea synthesis in rats

AIM

In patients with cirrhosis, endotoxemia is frequent and the vitally important capacity for urea synthesis is impaired. The patients' mortality of infection is markedly increased, which could be related to adverse metabolic effects of endotoxins. The effects of endotoxins on in vivo urea synthesis and on urea cycle genes during cirrhosis are unknown.

METHODS

We examined the effects of a low dose of 0.5 mg/kg ip lipopolysaccharide (LPS) on the basal urea nitrogen synthesis rate (UNSR), the capacity of urea nitrogen synthesis (CUNS), liver tissue mRNA levels of urea cycle enzyme genes, and on the metabolic liver function measured by the galactose elimination capacity (GEC) in rats with cirrhosis induced by bile duct ligation and in control animals.

RESULTS

LPS and cirrhosis + LPS decreased UNSR by 40% (P < 0.05). Cirrhosis and LPS each tended to decrease CUNS and cirrhosis + LPS decreased CUNS by 40% (P < 0.05). Cirrhosis and LPS each decreased the mRNA level of the gene for the flux-generating urea cycle enzyme carbamoyl phosphate synthetase (CPS) and the mRNA for the rate-limiting urea cycle enzyme arginine succinate synthetase (ASS) (P < 0.05). Cirrhosis + LPS left the mRNA level of CPS unchanged and decreased that of ASS (P < 0.05). The GEC did not differ among the study groups.

CONCLUSION

Endotoxemia in rats with experimental cirrhosis markedly impaired the ability of the animals' livers to synthesize urea, suggesting a pathophysiological mechanism underlying the severe consequences of endotoxemia in human cirrhosis.

Opposite effects on regulation of urea synthesis by early and late uraemia in rats

BACKGROUND & AIMS

Acute and chronic kidney failure lead to catabolism with loss of lean body mass. Up-regulation of hepatic urea synthesis may play a role for the loss of body nitrogen and for the level of uraemia. The aims were to investigate the effects of early and late experimental renal failure on the regulation of hepatic urea synthesis and the expression of urea cycle enzyme genes in the liver.

METHODS

We examined the in vivo capacity of urea nitrogen synthesis, mRNA levels of urea cycle enzyme genes, and N-balances 6 days and 21 days after 5/6th partial nephrectomy in rats, and compared these data with pair- and free-fed control animals.

RESULTS

Compared with pair-fed animals, early uraemia halved the in vivo urea synthesis capacity and decreased urea gene expressions (P<0.05). In contrast, late uraemia up-regulated in vivo urea synthesis and expression of all urea genes (P<0.05), save that of the flux-generating enzyme carbamoyl phosphate synthetase. The N-balance in rats with early uraemia was markedly negative (P<0.05) and near zero in late uraemia.

CONCLUSIONS

Early uraemia down-regulated urea synthesis, so hepatic ureagenesis was not in itself involved in the negative N-balance. In contrast, late uraemia up-regulated urea synthesis, which probably contributed towards the reduced N-balance of this condition. These time-dependent, opposite effects on the uraemia-induced regulation of urea synthesis in vivo were not related to food restriction and probably mostly reflected regulation on gene level.

Hyperammonemic coma--barking up the wrong tree

Hepatic encephalopathy and myxedema coma share clinical features: coma, ascites, anemia, impaired liver functions, and a "metabolic" electroencephalogram (EEG). Hyperammonemia, a hallmark of hepatic encephalopathy, has also been described in hypothyroidism. Differentiation between the 2 conditions, recognition of their possible coexistence, and the consequent therapeutic implications are of utmost importance. We describe a case of an 82-year-old woman with a history of mild chronic liver disease who presented with hyperammonemic coma unresponsive to conventional therapy. Further investigation disclosed severe hypothyroidism. Thyroid hormone replacement resulted in gain of consciousness and normalization of hyperammonemia. In patients with an elevated ammonia level, altered mental status, and liver disease, who do not have a clear inciting event for liver disease decompensation, overwhelming evidence of hepatic decompensation, or who do not respond to appropriate therapy for hepatic encephalopathy, hypothyroidism should be considered and evaluated.

Effect of lipopolysaccharide on in vivo and genetic regulation of rat urea synthesis

BACKGROUND

The acute phase response causes a negative nitrogen balance. It is unknown whether this involves regulation of hepatic urea synthesis.

METHODS

We examined the in vivo capacity of urea nitrogen synthesis (CUNS), mRNA levels of urea cycle enzyme genes and galactose elimination capacity (GEC) during moderate and severe acute phase response induced by low- and high-dose lipopolysaccharide (LPS) in rats.

RESULTS

Low-dose LPS doubled CUNS (P<0.05), decreased the mRNA level of the rate-limiting urea cycle enzyme (arginino succinate synthetase (ASS) by 26% (P<0.05) and did not change GEC. High-dose LPS did not change CUNS, decreased the mRNA level of the flux-generating enzyme carbamoyl phosphate synthetase (CPS) by 11% (P<0.05) and the rate-limiting urea cycle enzyme (ASS) by 27% (P<0.05) and almost halved GEC (P<0.05).

CONCLUSION

The moderate acute phase response up-regulated in vivo urea synthesis but had the opposite effect on gene level. The severe acute phase response decreased the functional liver mass that attenuated the increase in urea synthesis.