Spontaneously occurring cardiovascular lesions in commonly used laboratory animals

The search for new chemical entities which are clinically effective and do not adversely affect the cardiovascular system is an ongoing objective. In vivo studies designed to detect potential drug-induced cardiovascular toxicity typically utilize both rodent and non-rodent species. An important component of such studies includes the microscopic evaluation of tissues for histopathologic changes. A factor which could potentially complicate this type of evaluation relates to the potential for laboratory animals to develop natural or spontaneous pathological cardiovascular lesions. Some types of these naturally occurring alterations are similar to those induced by chemical compounds and thus could confound accurate interpretation. Accurate morphologic analysis becomes contingent upon the ability to distinguish spontaneous cardiovascular changes from actual drug-induced lesions. A summary of some of the more frequently reported spontaneous cardiovascular alterations in commonly-used laboratory animals is presented below. Special emphasis is given to the spectrum of spontaneous background myocardial pathology that might be encountered during preclinical studies conducted to identify potential cardiotoxic actions of anticancer agents.