Changes in contractile activity of the rabbit myocardium as a result of burn shock of varied duration

Abstract

Experiments were carried out on papillary muscles isolated from the rabbit heart 10, 60, or 180 min after thermal injury to the animal. Isometric contractions were recorded during stimulation of the preparation at changing frequencies (within the range from 0.1 to 2 Hz) and during poststimulation potentiation. The degree of disturbance of myocardial contractility as a result of burns was found to increase with an increase in the duration of burn shock: In all the papillary muscles isolated 3 h after burning and in 50% of those isolated 1 h after burning the “biphasic” frequency-strength (f-P) relationship characteristic of the normal myocardium was converted into “monophasic” (the amplitude of the contractions decreased progressively with an increase in frequency) and poststimulation potentiation, normally absent, appeared. After shock lasting 10 min, poststimulation potentiation was observed only in some preparations and no change in f-P was present. The normal inotropic relationships of the myocardial rhythm were restored after a twofold increase in [Ca⁺⁺]₀ or after prolonged (3–4 h) perfusion of the preparation with normal Tyrode solution. Changes in inotropic relationships of the myocardial rhythm in burn shock were similar to the changes in f-P observed after blockade of the calcium channels with compound D-600.