Regional differences in cardiac myocyte dimensions and number in Sprague-Dawley rats from different suppliers.

Previous experiments conducted in this laboratory have indicated that adult Sprague-Dawley rats obtained from Holtzman Company (H) have hearts that are significantly larger than those obtained from Charles River (CR). To investigate potential differences in cell size and number, isolated myocytes were prepared by retrograde coronary perfusion with collagenase. Cell volume (V) was measured with a Coulter Channelyzer, cell length (L) was measured directly, and cross-sectional area (CSA) was calculated from V/L. Cell number was calculated using data from isolated cells and whole-sectioned tissue. Although V for left and right ventricular myocytes was similar in CR and H rats, myocytes from CR tended to be shorter in L (P less than 0.001), but larger in CSA (N.S.) than myocytes obtained from H rats. In both H and CR, left ventricular V and CSA were greater (P less than 0.01) in endomyocardium than epimyocardium and middle myocardium. Values for V and CSA of right ventricular myocytes were less (P less than 0.01) than those from left ventricles in both H and CR. Hearts from H had 19% more myocytes than those from CR (P less than 0.05). Values for cellular dimensions from CR generally showed less variability than those from H. We conclude that significant regional differences in myocyte size are present in rats from both H and CR. Hearts from H rats have significantly more myocytes than those from weight-matched CR rats. Therefore, investigators should be aware that differences in heart weight and myocyte number can be found in rats of the same strain, but obtained from different suppliers.