Effect of metoprolol administration on renal sodium handling in experimental congestive heart failure

Background-Long-term metoprolol therapy improves cardiac performance and decreases mortality in patients with chronic congestive heart failure (CHF). This study examined the effect of long-term metoprolol therapy on renal sodium handling in an experimental rat model of CHF. Methods and Results-Rats with left coronary ligation and myocardial infarction-induced CHF were treated with metoprolol (1.5 mg.kg(-1).h(-1)) or vehicle for 3 weeks by osmotic minipump. They were then evaluated for their ability to excrete a short-term sodium load (5% body weight isotonic saline infusion over 30 minutes) and a long-term sodium load (change from low- to high-sodium diet over 8 days). All CHF rats had left ventricular end-diastolic pressure >10 mm Hg, and heart weight/body weight ratios averaged 0.68 +/- 0.02% (versus control of approximate to 0.40%). Compared with vehicle CHF rats (n = 19), metoprolol CHF rats (n = 18) had lower basal values of mean arterial pressure (122 +/- 3 versus 112 +/- 3 mm Hg) and heart rate (373 +/- 14 versus 315 +/- 9 bpm) and decreased heart rate responses to intravenous doses of isoproterenol. During short-term isotonic saline volume loading, metoprolol CHF rats excreted 54 +/- 4% more of the sodium load than vehicle CHF rats. During long-term dietary sodium lending, metoprolol CHF mts retained 28 +/- 3% less sodium than vehicle CHF rats. Conclusions-Metoprolol treatment of rats with CHF results in an improved ability to excrete both short- and long-term sodium loads.