Myocardial morphometric characteristics in swine.

We have quantified the ultrastructure of myocardial cells in tissue samples obtained from six adult normal Yucatan swine. Tissue samples were obtained from 20 different sites in the left ventricle, right ventricle, and interventricular septum. The samples were processed for electron microscopy and quantitative morphometric analysis. The percent relative volumes of myofibrils, mitochondria, transverse tubular system, sarcoplasmic reticulum, and clear intracellular space were determined using stereological morphometric methods. Overall, the data were distributed homogeneously among the 20 individual sites. However, when certain subcellular components were examined regionally, some differences appeared. The mitochondrial:myofibril volume ratios were significantly increased in the left ventricle and interventricular septum compared to the right ventricle. They also were greater in the endocardial region compared to the epicardium, which is consistent with higher metabolic activity of these zones. Similarly, the sarcoplasmic reticulum:myofibril ratio was greater in the endocardial region vs. the epicardial region and the basal layer compared to the mid-layer, suggesting the greater need for provision of calcium ions in these particular zones. Since the swine is a convenient large animal for physiological studies, the results indicate that swine can also be used for quantitative morphometric measurements of myocardial changes in normal and pathologic hearts, and for the study of regional changes in various layers and regions of heart walls.