THE ANATOMICAL RECORD 215420-426 (1986) zy Regional Differences in Myocyte Size in Normal Rat Heart A. MARTIN GERDES, JO zyxwvuts A. MOORE, JOSEPH M. HINES, P.A. KIRKLAND, AND SANFORD P. BISHOP zyxwvu University of South Florida, College zyxwvut of Medicine, Department of Anatomy, Tampa, FL (A.M.G.,J.A.M.,J.M.H.); Department ofPathology, Birmingham, AL(P.A.K.,S.P.B.) ABSTRACT Three independent methods were evaluated in an effort to obtain reliable values for myocyte size in adult Sprague-Dawley rats. Cell volume was determined from isolated myocytes by a Coulter Channelyzer system. Cell volume was also determined from the product of length and cross-sectional area of isolated myocytes. Additionally, myocyte cross-sectional area was measured morphometri- cally from electron micrographs of whole perfusion-fixed tissue. A major goal was to determine if anatomical methods used to measure cell volume produce values com- parable to the more expeditious and objective Coulter Channelyzer method. The results of these experiments showed that myocyte dimensions obtained from all three techniques were similar. The second major objective was to use the above-mentioned techniques to evaluate regional differences in myocyte size. Myocyte cross-sectional area and volume were significantly larger in the endomyocardium than in the epimyocardium of the left ventricle. Right ventricle myocytes had significantly smaller volumes and cross- sectional areas than did left ventricle myocytes. There were no regional differences in cell lengths. We conclude that 1) the Coulter Channelyzer system gives values for isolated myocyte volume that are similar to values obtained with histometric techniques; 2) values for isolated myocyte cross-sectional area were representative of values ob- tained from myocytes in whole-sectioned tissue; 3) significant regional differences in myocyte size are present in adult rat hearts; and zyxwv 4) regional variations in myocyte size are due to differences in myocyte cross-sectional area rather than cell length. Estimation of myocyte size not only provides informa- tion regarding cellular hypertrophy (or atrophy), but is also useful in estimating myocyte numbers. Rakusan and Korecky (1983) recently reviewed biochemical and histometric methods for estimating myocyte size and numbers. Rakusan et al. (1983) have also shown a cor- relation between biochemical and histometric counts of myocyte numbers obtained from aortic banded rats. Comparison of absolute values (obtained from both tech- niques) for a given group, however, differed by as much as 20%. Although cell size comparisons from control and experimental animals may be valid when produced in the same laboratory, a reliable method for obtaining absolute myocyte size has not been outlined. The re- ported range of 8 million to 90 million myocytes per heart for adult rats (Black-Schaffer et al., 1965; Costabel and Adler, 1980) underscores the inherent difficulty in obtaining reproducible data. In an effort to reliably determine myocyte size, numer- ous experiments have been conducted in our laboratory over the past 3 years. Three independent techniques were used to quantitate myocyte size. Two methods uti- lized isolated myocytes and the other employed whole- sectioned tissue. Each technique yielded similar abso- lute values for myocyte size. In recent years, several authors have noted regional differences in myocyte size in adult rat heart (Loud et al., 1978; Tomanek, 1979; Gerdes et al., 1979; Bishop et al., 1979). Each reported that myocyte cross-sectional area was larger in the endomyocardium than in the epimyocardium (differences were not statistically signif- icant in Tomanek, 1979, and in Bishop et al., 1979). Additionally, right ventricle myocytes were signifi- cantly smaller than those from left ventricles (Bishop et al., 1979). None of the above-mentioned studies, how- ever, employed an alternate method to validate cell siz- ing data. In this study, regional differences in myocyte size were evaluated from both whole tissue and isolated myocytes. The results confirm that significant regional differences in myocyte size are present in adult Sprague- Dawley rats. METHODS Female Sprague-Dawley rats were obtained from the Holtzman Company, (Madison, WI). Data are reported for rats of three different body weights (approximately 150, 300, and 350 gm body weight). Many of these ani- Received January 15,1986; accepted February 28, 1986. zy 0 1986 ALAN R. LISS, INC.