ON THE RELATIONSHIP OF CATECHOLAMINES AND THYROID ACTIVITY TO VENTRICULAR FIBRILLATION DURING HYPOTHERMIA IN DOGS

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Abstract
The possible significance of endogenous catecholamines in the production of hypothermic ventricular fibrillation has been investigated.It is shown that in dogs under pentobarbitone anesthesia, neither iproniazid nor phenoxybenzamine pretreatment reduces the incidence of ventricular fibrillation following coronary occlusion during hypothermia. Reserpine pretreatment markedly reduced both the catecholamines content of the left ventricle and the incidence of ventricular fibrillation. This protective action of reserpine can be counteracted by combined pretreatment with liothyronine sodium, although the catecholamines of the heart remained at a low level. Conversely, thyroidectomy and methimazole treatment also greatly reduced the incidence of ventricular fibrillation without significantly reducing cardiac catecholamines. These experiments reveal no correlation between the ventricular catecholamines content and the incidence of ventricular fibrillation. It is suggested that the protective effects of reserpine and thyroidectomy or antithyroid treatment might be due to depression of tissue metabolism.

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