Volumetric Changes in the Components of Left Ventricle Myocardium of Spontaneously Hypertensive Rats Following Exercise and ACE Inhibitor Treatment

This study was designed to test the possible effects of a combination of physical and pharmacological therapy intervention on myocardial structure of the left ventricle in spontaneously hypertensive rats (SHR). Forty 12 weeks old spontaneously hypertensive rats were divided into four groups of sedentary, Sed as controls, exercise only , (Exer), lisinopril only 20mg/kg/day, (Lis), and exercise + lisinopril, (LisExer). Exercise training was performed on a treadmill (5m/min.) for 60 minutes/day, 5 days/week for 10 weeks. At the end of 10 weeks, all the rats were terminally anaesthetised, the heart was arrested in diastole by intravenous procaine and whole animal perfusion fixation through the abdominal aorta was carried out using Karnovsky's fixative (Ph 7.24). The heart was removed and left ventricle plus the interventricular septum was serially sectioned at a thickness of three millimetres. One piece was randomly chosen, and embedded in JB4 resin. Six sections were obtained from each block, stained with toluidine blue:acid fucin. Measurement of volume fraction V_f, of myocardial components was carried out using Histometrix MIL6 Ver 1.0 stereology software ( Kinetic imaging Ltd.). Mean volume fraction, V_f of capillaries in Sed. group was 0.114 ± 0.01 (SEM). This was significantly increased in LisExer group. The volume fraction of muscle in Sed group was 0.795 ± 0.02 (SEM). This was significantly decreased in Lis but unchanged in Exer group. Capillaries V_f was significantly higher in LisExer as compared to Lis or Exer groups (p<0.05). Muscle V_f was not different between LisExer and Lis groups. The outcome of these changes could well be a better enhancement of cardiac performance in hypertension by combined exercise and ACE inhibitor treatment than either of the interventions alone.