Abbott TDx, Dade Stratus, and Du Pont aca automated digoxin immunoassays compared with a reference radioimmunoassay method.

Automated digoxin immunoassays with the Abbott TDx, Dade Stratus, and Du Pont aca were evaluated against an RIA similar to the Centers for Disease Control Candidate Reference Method. All three automated methods correlated poorly with the reference method. Particularly disconcerting were the falsely increased values (up to 0.6 micrograms/L) obtained by the Stratus for blank specimens. We discuss the inaccuracies of the results in terms of sample matrix effects, calibrator problems, lot-to-lot reagent variation, and our laboratory requirements. We strongly support the acceptance of the CDC Candidate Reference Method for digoxin and the establishment of a standardized protocol for determining the accuracy of digoxin measurements.

Unconjugated hyperbilirubinemia in chronic persistent hepatitis.

We studied a young man with persistent elevation of transaminases and indirect bilirubin following acute viral hepatitis. Liver biopsy showed chronic persistent hepatitis, and clinical evaluation was otherwise negative for significant liver disease. The indirect-reacting serum bilirubin rose after both caloric restriction and intravenous nicotinic acid, responses believed by some to be characteristic of Gilbert's syndrome. Fasting and postprandial serum bile acid conjugates were not elevated. These results suggest that "Gilbert's-like" aberrations in bilirubin metabolism may be part of the spectrum of chronic persistent hepatitis.

Synthetic sulfur-containing amino acids. Inhibition of transport systems in S37 ascites tumor cells.

The preparation of a series of synthetic sulfur-containing amino acids is described. These compounds included heterocyclic analogues of L-cysteine, DL-norcysteine, and DL-homocysteine. The amino acids were assessed for their ability to inhibit the neutral amino acid transport systems of the Sarcoma 37 ascites tumor cell and their inhibitions were compared with those of L-methionine and L-ethionine. Transport studies indicated that the amino acids synthesized were capable of inhibiting the uptake of [3H]-L-histidine in the S37 cell.

Specificity in enzyme inhibition. 3. Synthesis of 5-substituted 2,2-dimethyl-4-imidazolidinones as inhibitors of tyrosine decarboxylase and histidine decarboxylase.

2,2-Dimethyl-4-imidazolidinone derivatives of the alpha-amino acids DL-phenylglycine (1), DL-phenylalanine (2), L-tyrosine (3), L-histidine (4), and L-tryptophan (5) were prepared in order to assess their specificity in inhibiting amino acid decarboxylases. Treatment of th alpha-aminonitriles with acetone in the presence of base and heat or treatment of the alpha-amino amides with acetone gave the title compounds in 48-85% yield. The compounds afforded moderate ability to inhibit the decarboxylation of L-phenylalanine, L-tyrosine, or L-histidine in vitro, using crude enzymes. 3 was a better inhibitor of tyrosine decarboxylase (S. faecalis) than 2. 4 and 5 were comparable to 3 in inhibiting tyrosine decarboxylase. 4 was more selective in inhibiting purified histidine decarboxylase (Cl. welchii) than 5, which was inactive. 4 was inactive against fetal rat histidine decarboxylase in vitro.