Spontaneous cardiomyopathy in young Sprague-Dawley rats: evaluation of biological and environmental variability.

Cardiovascular safety signals in nonclinical studies remain among the main reasons for drug attrition during pharmaceutical research and development. Drug-induced changes can be functional and/or associated with morphological alterations in the normal heart histology. It is therefore crucial to understand the normal variations in histology to discriminate test article-related changes from background lesions. Rodent progressive cardiomyopathy is probably the most commonly encountered change in control animals of nonclinical toxicity studies. A multisite study mimicking standard short-term toxicity studies using young male Sprague-Dawley rats was performed to better characterize this finding. Using an enhanced sectioning method for this research study, it was observed that the incidence of background cardiomyopathy was 100%. The vast majority of the microscopic findings were inflammatory in nature, with associated necrotic changes (defined as necrosis/inflammatory cell infiltrate) and these changes were mainly located in the myocardium of the mid region of the ventricles (the left side being predominantly affected). The monitored environmental factors in this study (multiple facilities, study duration, handling) did not have an effect on the incidence or severity of the spontaneous cardiomyopathy. In addition, cardiac-specific serum troponin levels were measured and were within the published control range.