Stereology of the myocytes in young and aged rats

PURPOSE: To determine the myocardial quantitative changes comparing young and aged animals by using the stereology. METHODS: Thirty rat hearts were studied (15 rats aged 3 months and 15 other rats aging 15 months). The hearts were removed, weighed, fixed in 10% buffered formaldehyde solution, embedded in paraffin, cut in 7µm thick slices and stained with HE and picro-sirius stains. In each group we counted 15 random microscopic fields. The following parameters were studied: Vv(myocyte) and Vv(interstitium)(%) (the volume densities of the cardiac myocyte and interstitium, determined by the point-counting method), and Nv(myocyte) (1/mm³) (the numerical density of the cardiac myocytes, determined with the disector method). The total number of myocytes (N[myocyte]) and the mean volume of the myocytes (V[myocytes]) were also determined. The differences were tested by the Mann-Whitney test.RESULTS: Cardiac weight increased from 1.1 to 1.7g, the Vv(myocyte) decreased from 76.7 to 72.2%, the Vv(interstitium) increased from 23.3 to 27.8%. The Nv(myocyte) and the N(myocyte) decreased from 14.76×10(4) to 6.19×10(4)/mm³ and 15.64×10(4) to 10.72×10(4) myocytes, respectively. Simultaneously, the V(myocyte) increased from 5.42×10³ to 13.26×10³mm³. These differences were statistically significant (p<0.05). CONCLUSION: Myocardial changes, comparing young rats with aged ones suggest loss of myocytes (increased apoptosis?) with simultaneous myocyte hypertrophy.