Norepinephrine Stores and Contractile Force of Papillary Muscle from the Failing Human Heart

The relation between cardiac norepinephrine concentration and the functional state of the myocardium was studied in left ventricular papillary muscles removed from patients with congestive heart failure at the time of mitral valve replacement. Myocardial function was assessed by determining the maximum isometric active tension that the papillary muscle could develop in an in vitro system, and by measuring the increase in active tension in response to the norepinephrine-releasing sympathomimetic amine, tyramine. The norepinephrine concentration averaged 0.36 µg./Gm. in 17 muscles. In eight of these a response to tyramine was observed with a 21-per cent increase in active tension, and the norepinephrine concentrations averaged 0.53 µg./Gm.; in the other six muscles tested with tyramine no positive inotropic response was observed, and the norepinephrine concentration was significantly lower, averaging 0.16 µg./Gm. The maximum active tension in 17 muscles averaged 1.78 Gm./mm. 2 , and a significant positive correlation between the maximum tension and the norepinephrine concentration of the individual muscles was observed. In the eight muscles responding to tyramine, the maximum tension observed, 2.34 Gm./mm. 2 , was significantly greater than that observed in the six muscles unresponsive to tyramine, 0.64 Gm./mm. 2 It is concluded that norepinephrine depletion appears to be associated with defective myocardial function although no causal relationship between these two abnormalities has been established.