Studies on human low serum IgD phenotype and Gm markers.

The human "low serum IgD phenotype" was studied by simultaneous Gm typing and IgD immunoassay of several populations. An association between Gm (f+b+) haplotype and low human IgD was confirmed and extended to the "low serum IgD phenotype"--as defined from population distribution and genetic studies by Dunnette et al. 1978.

Immunochemical studies of antisera to human fibrinopeptide-B.

The immunochemical specificity of rabbit antisera to human fibrinopeptide-B (FPB) has been studied by comparing the relative abilities of FPB and of various proteins and peptides containing the NH2-terminal segment of the B beta-chain of human fibrinogen to inhibit the binding of a radioiodinated FPB derivative by each of seven anti-FPB sera. Anti-FBP sera varied in the extent to which they cross-reacted with fibrinogen, the NH2-terminal disulfide knot of fibrinogen (N-DSK), B beta 1(Pyr)-118(Met), B beta 1(Pyr)-42(Arg), and desarginyl-FPB. Anti-FPB sera have been identified that discriminate effectively between FPB and larger FBP-containing peptides; such antisera can be used to measure FPB in the absence of the larger peptides or to demonstrate the presence of larger peptides such as B beta 1(Pyr)-42(Arg) in extracts of clinical plasma samples by means of an increase in FPB immunoreactivity following thrombin treatment.

The development and application of a radioimmunoassay for dihydrodigoxin, a digoxin metabolite.

The cardioinactive digoxin metabolite, dihydrodigoxin, has been conjugated to bovine serum albumin and to bovine pancreatic ribonuclease by the periodate oxidation method. Rabbits immunized with the dihydrodigoxin-bovine serum albumin conjugate formed antibodies which bound a radioiodinated dihydrodigoxin-ribonuclease conjugate. This binding was inhibited by dihydrodigoxin.

Inactivation of digoxin by the gut flora: reversal by antibiotic therapy.

In approximately 10 per cent of patients given digoxin, substantial conversion of the drug to cardioinactive, reduced metabolites (digoxin reduction products, or DRPs) occurs. The site and clinical importance of this conversion is unknown. In four normal volunteers taking digoxin daily for four weeks, urinary excretion of DRPs was greatest after a poorly absorbed tablet was ingested, and least after intravenous administration, Stool cultures from subjects known to make DRPs in vivo ("excretors") converted digoxin to DRPs; cultures from nonexcretors did not.