Direct and reflex effects of nitroglycerin on coronary and left ventricular dynamics in conscious dogs

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Abstract

The effects of intravenous and sublingual glyceryl trinitrate (nitroglycerin), 40 μg/kg, were studied on coronary blood flow and resistance, left ventricular (LV) pressures (P) and diameters (D), rate of change of pressure (dP/dt), (dP/dt)/P, and on the velocity (V) of myocardial fiber shortening in conscious dogs. Nitroglycerin i.v. caused substantial coronary vasodilatation prior to any changes in systemic hemodynamics. Mean coronary flow increased by a maximum of 47 ml/min and coronary sinus Po2 rose from 16 to 26 mm Hg while pressure and diameter began to fall, and heart rate began to rise. After the maximal fall in mean arterial pressure (—26 mm Hg), a secondary peak in coronary flow occurred which was associated with increases in heart rate (100 beats/min), (dP/dt)/P (22%), and isolength V (12%). Beta blockade prevented the reflex increases in contractility but only a part of the reflex tachycardia; the remainder was prevented by cholinergic blockade. Maintaining heart rate constant minimized the decreases in LV D and increases in contractility. When the reflex inotropic and chronotropic effects were prevented by a combination of atrial pacing and beta blockade the early coronary vasodilatation was unaltered, but the later coronary vasodilatation was minimized.

Authors

Stephen F. Vatner, Charles B. Higgins, Ronald W. Millard, Dean Franklin