Radioimmunoassay of lactate dehydrogenase, H forms

Antisera to H4-lactate dehydrogenase (LDH) were elicited in rabbits, against both human (h) and porcine (p) isoenzymes. 125I-labelled H4-LDH was prepared by electrolytic iodination. A simple and fast procedure (1-h incubation for clinical assays) was set up by using polyethylene glycol for the bound-free separation. The results obtained in the antiserum characterization indicated that the heterologous homotetramer, M4 was completely discriminated in the porcine system, while a weak cross-reaction with human antisera resulted. In both cases, for the hybrid forms, a cross-reactivity level related to the stoichiometric contents of the H-subunit in the tetramers was observed. The H4-LDH from other species was found to be much more effectively disinguished in the porcine than in the human system. The assay for human LDH was further validated in terms of analytical suitability and clinical response. For healthy subjects the mean concentration was 0.46+/-19 micrograms/ml (mean+/-SD). Patients with acute myocardial infarction had levels ranging from 1.2 to 5.9 micrograms/ml.