Effect of nitroglycerine on coronary circulation and cardiac metabolism

Nitroglycerine administered intravenously to dogs under chloralose anesthesia elicits a biphasic effect. During the first phase, it causes an increase in heart rate, a decrease in mean arterial bloodpressure and a rise in cardiac output, coronary blood flow and myocardial oxygen consumption. During the second phase, the heart rate remains elevated and the arterial bloodpressure remains below control, but cardiac output, coronary blood flow and myocardial oxygen consumption decrease to or below control values. During both phases, the myocardial oxygen arteriovenous difference is decreased below its control value because of a rise in the oxygen content of the coronary sinus blood. It is concluded that nitroglycerine first increases the myocardial oxygen consumption less than the coronary blood flow, then may decrease the oxygen consumption more than the coronary flow.