Variable effects of intracoronary nitroglycerin on myocardial blood flow and segmental shortening according to dose and degree of coronary occlusion.
The effects of intracoronary nitroglycerin were determined in 21 open-chest dogs. Six dogs with severe stenosis (25 mm Hg diastolic perfusion pressure) and nine dogs with moderate stenosis (40 mm Hg) received a 12 micrograms bolus followed by 44 micrograms/min intracoronary nitroglycerin. In addition, six dogs with moderate stenosis (40 mm Hg) received 5 micrograms followed by 5 micrograms/min nitroglycerin. Myocardial blood flow was measured with radioactive microspheres and segment shortening with ultrasonic crystals. At 40 mm Hg, high-dose but not low-dose nitroglycerin raised epicardial blood flow, while at 25 mm Hg nitroglycerin had no effect. Subendocardial blood flow was not affected in any group. Partial occlusion resulted in a decrease in segment shortening in the 25 mm Hg group but not at 40 mm Hg. High-dose nitroglycerin had no effect on shortening at either level of occlusion. Thus, in the presence of coronary vascular reserve, high-dose nitroglycerin may overcome coronary autoregulation. A dose equivalent to one that simulates the amount of nitroglycerin delivered to the coronary circulation by a systemic infusion did not affect myocardial blood flow. In addition, even a large dose of nitroglycerin did not affect segment shortening.
D000818:Animals; D001794:Blood Pressure; D003326:Coronary Circulation / Q000187:drug effects*; D003327:Coronary Disease / Q000473:pathology / Q000503:physiopathology*; D003331:Coronary Vessels / Q000473:pathology; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D009200:Myocardial Contraction / Q000187:drug effects*; D005996:Nitroglycerin / Q000008:administration & dosage*
D005996:Nitroglycerin