Diminished Inotropic Response to Catecholamines in the Aged Myocardium

Abstract

It is known that the cardiovascular response to stress in both intact animals and in man diminishes with advancing age. In order to define the role of the myocardium in these age associated changes, the direct inotropic response to left ventricular traveculae carneae from young adult (6 mo) and aged (24 mo) rats was examined during exposure to catecholamines. The muscles were stimulated to contract isometrically at 24 beats per min at 29°C Krebs-Ringer bicarbonate solution, modified by lowering the Ca⁺⁺ to 1 . 0mM, the Mg⁺⁺ to 0 . 6mM, and by adding glucose to a concentration of 16mM. At control, active tension (AT) , maximum rate of tension development (dT/dt) and contraction duration (CD) , measured as the interval from the onset of tension development to the time tension fell to one-half of its maximum value were: