BETA-ADRENERGIC-MEDIATED IMPROVEMENT IN LEFT-VENTRICULAR FUNCTION BY EXERCISE TRAINING IN OLDER MEN

To test the hypothesis that the training-induced improvement in the ag e-related decline in left ventricular (LV) function is mediated by enh anced inotropic responses to P-adrenergic stimulation, 10 sedentary he althy men, 65 +/- 1 yr (mean +/- SE) of age, exercised for 9 mo, which resulted in a 28% increase in aerobic exercise capacity. Training ind uced a greater increase in LV systolic shortening, assessed with two-d imensional echocardiography, in response to isoproterenol with a steep er slope of the fractional shortening-end-systolic wall stress (sigma( es)) relationship and an upward shift of the sigma(es)-systolic diamet er relationship without an acute increase in heart rate or preload. Th e increase in the early-to-late diastolic flow velocity ratio, normali zed for heart rate and preload, in response to isoproterenol was large r after training. LV systolic reserve and cardiac output during peak e xercise were higher after training. beta-Adrenergic blockade with esmo lol HCl abolished the adaptive increases in LV systolic reserve capaci ty and cardiac output during peak exercise in the trained state. The r esults suggest that one of the underlying mechanisms responsible for t he adaptive increase in LV systolic function in response to exercise t raining is an enhanced inotropic sensitivity to catecholamines. Furthe rmore, the enhanced inotropic responses are associated with increased diastolic filling.