Effects of captopril on left ventricular structure and function in SHR with established hypertension

While antihypertensive therapy is considered to be an important clinical intervention in hypertensive patients, its effects on cardiac structure and function have not been intensely evaluated. In this study we tested the hypotheses that lowering blood pressure (BP) with the angiotensin I-converting enzyme inhibitor captopril, would: 1) normalize left ventricular mass and increase the cardiocyte mitochondria/myofibrils volume (Vmito/Vmyo) ratio; and 2) not compromise peak ventricular performance. We treated 16-week-old SHR and WKY with captopril (40-80 mg/kg) and hydrochlorothiazide (500 mg/l) via their drinking water. After six weeks of treatment peak cardiac performance was measured during rapid volume overload. Tissue samples from the left ventricular wall were analyzed by electron microscopy and stereology. Captopril lowered BP in SHR and WKY but had no affect on the left ventricular/body weight ratio. The only intracellular change in treated SHR was an increase in sarcoplasmic volume density. Treated WKY exhibited decreased midmyocardial mitochondrial volume density. At peak cardiac output, acceleration of flow and cardiac index were not affected by treatment. Stroke work at peak cardiac output was decreased in the treated groups due to a decrease in mean arterial pressure. In addition, captopril treatment resulted in a shift of the cardiac output (CO)-left ventricular end diastolic pressure (LVEDP) curves, such that LVEDP at peak cardiac output was approximately 50% less in the treated groups compared to their respective control groups. Although captopril was efficacious in lowering BP, it is suggested that lowering BP with this agent does not, at least within six weeks, lead to a reversal of hypertrophy or to a significant alteration in the volume densities of myofibrils and mitochondria. However, an important effect of this antihypertensive drug which may be of clinical significance, is that it leads to a leftward shift of the CO-LVEDP curve in both hypertensive and normotensive rats.