Cardiac specific troponin-I release in canine experimental myocardial infarction: development of a sensitive enzyme-linked immunoassay.

A canine model of experimental myocardial infarction has been used to investigate the release of troponin-I as a specific diagnostic indicator of cardiac necrosis. An enzyme-linked immunoassay was established to detect canine cardiac troponin-I in serum. Polyclonal antisera to cardiac troponin-I showed low cross-reactivity with skeletal muscle troponin-I which was completely removed by immunoadsorption. The cardiac specific ELISA time was 5 to 6 h. Assay sensitivity was 4 ng cardiac troponin-I/ml with an upper limit of 200 ng/ml in neat serum. Mean normal circulating levels of cardiac troponin-I were 15.6 ng/ml compared with an estimated 11 ng/ml in man [Cummins, B. et al. Am Heart J 113, 1333-1344 (1987)]. After experimental infarction, cardiac troponin-I was detectable within 4 to 6 h and peaked between 10 to 16 h post-ligation. Cardiac specific creatine kinase-MB isoenzyme was released with a similar initial time course. Mean peak cardiac troponin-I and CK-MB were elevated 6- and 10-fold respectively. Cardiac troponin-I levels were elevated for up to 200 h post-ligation compared to a maximum of 100 h for CK-MB. The prolonged time course of troponin-I release was comparable to that seen clinically [Cummins, B., et al. Am Heart J 113, 1333-1344 (1987)]. Histochemical infarct size correlated well with CK-MB but less so with troponin-I release. This may reflect the complex nature of intracellular troponin-I degradation and loss from necrotic cardiac tissue.