The supersensitivity of the rat cardiovascular system to epinephrine after repeated injections of ethylene glycol dinitrate

Abstract

The sc injection of 65 mg/kg ethylene glycol dinitrate (EGDN), once daily, 5 days a week, for 5 weeks in the rat does not lead to any changes in the resting ECG, heart rate, or blood pressure once the immediate effects of the presence of unmetabolized EGDN in the blood have passed. Five hours after the last injection of EGDN the heart of the anesthetized rat is subsensitive to epinephrine-induced arrhythmias, and 24 hr after the last injection both the heart and blood pressure are supersensitivity to epinephrine. The absence of supersensitivity in the pithed rat indicates that the pressor supersensitivity of the intact, anesthetized rat is not due to the muscle cells of the cardiovascular system per se, but must involve the nervous system in some way. It is suggested that there may be some temporary deficiency in the circulatory mechanisms, either in the pressoreceptors, the higher autonomic centers, or the peripheral ganglia. The supersensitivity of the heart is not due to electrolyte changes in the myocardium. It is suggested that the pressor supersensitivity may lead to myocardial sensitization by virtue of the extra-large rise in blood pressure.