10 Stereological estimation of absolute volumes of myocardium and ventricular end diastolic volume of the left ventricle following combination of exercise and ACE inhibitor lisinopril in spontaneously hypertensive rats

This study was designed to test the hypothesis that in a hypertensive heart, combination of moderate exercise and ACE inhibitor treatment is better than either of the two alone in reducing myocardial hypertrophy and increasing end diastolic volume of the left ventricular cavity. Sixty-five 12-week-old spontaneously hypertensive rats (SHR) were divided into four groups of sedentary (S) as controls (n = 16), exercise (E, n = 17), lisinopril 20 mg kg−1 (L, n = 16), and exercise + lisinopril 20 mg kg−1 (LE, n = 16). Exercise training was performed on a motor treadmill (speed = 20 m min−1) for 60 min day−1, 5 days a week. At the end of 12 weeks, all the rats were anaesthetized with i.p. sodium pentobarbitone, and the heart was arrested in diastole by intravenous xylocaine. Whole animal perfusion fixation through the abdominal aorta was carried out using Karnovsky's fixative. The heart was removed and the left ventricle plus the interventricular septum were dissected out. This was embedded in molten paraffin wax and serially sectioned at a thickness of 6 mm using a small object slicer. Outlines of one face of all the serial sections were traced on a transparent sheet and used to measure the absolute muscle volume and ventricular end diastolic volume (VEDV) using the Cavalieri method. Absolute volume of left ventricle myocardium was significantly smaller (P 0.05). These results indicate that in SHRs myocardial hypertrophy is intensified by exercise and reduced by administration of lisinopril. Exercise alone increases VEDV whilst lisinopril alone decreases myocardial hypertrophy and increases VEDV. Combination of exercise and lisinopril significantly changed the myocardial volume and VEDV more than either of the two alone. This combination may be more beneficial to the overall myocardial performance.