Cardiac Norepinephrine Stores and the Contractile State of Heart Muscle

Author:

SPANN JAMES F.1,SONNENBLICK EDMUND H.1,COOPER THEODORE1,CHIDSEY CHARLES A.1,WILLMAN VALLEE L.1,BRAUNWALD EUGENE1

Affiliation:

1. Cardiology Branch, National Heart Institute Bethesda, Maryland and the Department of Surgery, St. Louis University School of Medicine St. Louis, Missouri

Abstract

In order to assess the role played by endogenous norepinephrine (NE) stores in the intrinsic contractile state of cardiac muscle, the right ventricular papillary muscles from normal cats and cats with cardiac NE depletion produced by chronic cardiac denervation or reserpine pretreatment were studied. The contractile state of NE-depleted ventricular myocardium was found to be normal. The resting and active length-tension curves, the forcevelocity relations, and the augmentation of isometric tension achieved by paired electrical stimulation and by increasing frequency of contraction were not depressed in either group of NE-depleted muscles. Similarly, no changes in the absolute refractory period and electrical excitability were observed. It is concluded that cardiac stores of NE are not fundamental for maintaining the intrinsic contractile state of the myocardium. Further, release of endogenous NE from cardiac muscle does not appear to play an essential role in the mediation of the positive inotropic effects of increasing frequency of contraction or of sustained postextrasystolic potentiation.

Publisher

Ovid Technologies (Wolters Kluwer Health)

Subject

Cardiology and Cardiovascular Medicine,Physiology

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