Ornithine, serum levels

Transamination is not restricted to a-amino groups. The 5-amino group of ornithine—but not the e-amino group of lysine—readily undergoes transamination. Serum levels of aminotransferases are elevated in some disease states (see Figure 7-11). 

A urea cycle enzyme found mainly in the liver and kidney. High serum levels are found in conditions where there is hepatocellular damage such as hepatitis. A congenital deflciency of the enzyme has also been described (ornithine carbamyl transferase deficiency). 

The liver appeared to be a target organ for hexachloroethane following oral administration. When one dose of 500 mg/kg was administered in an olive oil aqueous emulsion to male sheep, the levels of glutamate dehydrogenase, sorbitol dehydrogenase, ornithine carbamyl transferase, and aspartate aminotransferase in serum increased in the 2-day period after compound administration and then normalized (Fowler 1969b). Hexachloroethane had no effect on bromsulphthalein uptake from the blood by liver cells, but the transfer of this dye to bile was reduced in sheep exposed to doses of 500-1,000 mg/kg/day. 

Gebhardt, R., Beckers, G., Gaunitz, F., Haupt, W., Jonitza, D., Klein, S., Scheja, L. Treatment of cirrhotic rats with L-ornithine-L-aspartate enhances urea synthesis and lowers serum ammonia levels. X. Pharmacol Exper. Ther. 1997 283 1-6... 

Ammonia metabolism within the muscle may be improved by the administration of L-omithine-L- aspartate (LOLA). Controlled trials suggest that enteral and parenteral formulations of ornithine aspartate significantly reduce blood ammonia levels and have useful therapeutic effects in patients with cirrhosis and encephalopathy (Kircheis et al., 1997 Stauch et al., 1998). Poo et al. (2006) recently showed in a randomized, lactulose-controlled study of oral ornithine-aspartate in 20 patients with clinically overt HE that LOLA in contrast to lactulose significantly improved parameters of mental status, number connection test scores, asterixis scores and EEG. Both lactulose and LOLA reduced serum ammonia levels and improved quaUty of life scores. Since only 20 patients were included in this study the results cannot be considered proof for the superiority of LOLA compared to lactulose, while the data underscore the effect of both agents. Ornithine aspartate is well tolerated in general. From a theoretical point of view the combination of disaccharides and ornithine aspartate may be useful in patients with insufficient efficacy of only one of the two drugs. 

Certain amino acids are maintained at higher concentration in blood cells compared to plasma. This is the case for taurine, glutamate, aspartate, glutathione and for argininosuccinate, when present. Thus, hemolysis often increases the levels of these amino acids in plasma or serum. Hemolysis also releases the enzyme arginase, which hydrolyzes arginine to ornithine. 

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