Effects of nitroglycerin on cardiac function and regional blood flow distribution in conscious dogs

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Abstract
The effects of i.v. infusion of nitroglycerin (NTG), 8 and 32 .mu.g/kg .cntdot. min for 7 min, and of sublingual NTG, 1.2 mg, were examined on direct and continuous measurements of systemic, coronary and regional hemodynamics, left ventricular (LV) dimensions, pressures and myocardial contractility in conscious dogs. NTG induced sustained reductions in LV dimensions and transient increases in heat rate and dP/dt [change of pressure with time], and decreases in mean arterial pressure. Initially NTG increased cardiac output and flows to the coronary, mesenteric, renal and iliac beds, while systemic and regional vascular resistances fell. Later, cardiac output, cardiac work and mesenteric and iliac flows fell significantly below control, and significant vasoconstriction in the systemic as well as mesenteric, iliac and coronary beds was observed at a time when LV end-diastolic dimensions were still significantly reduced. Peripheral vasoconstriction was not observed with systemic NTG in deafferented dogs or when NTG, 1 .mu.g/kg .cntdot. min, was infused intra-arterially into the iliac bed. Thus, systemic NTG induces a biphasic response consisting of initial arteriolar vasodilation followed by vasoconstriction in the mesenteric, iliac, coronary and systemic beds, which is presumably due to longer lasting effects on preload and to secondary reflex responses to the drug.