Redistribution of coronary microvascular resistance produced by dipyridamole.
This study assessed the redistribution of coronary microvascular resistance during vasodilation produced by dipyridamole. Measurements of microvascular diameter and pressure in the beating left ventricle of anesthetized cats were accomplished by means of a computer-controlled system that enabled measurements in the beating heart. Resistances of coronary arteries, microvessels, and veins were calculated from the quotients of the pressure gradient across each vascular compartment and myocardial perfusion (radioactive microspheres). Administration of dipyridamole increased coronary blood flow from 1.80 +/- 0.09 to 6.42 +/- 0.31 ml.min-1. g-1 (P less than 0.05). During control conditions, 25 +/- 8% of total resistance occurred in coronary arteries (proximal to 170 microns), 68 +/- 8% of total resistance was in coronary microvessels (between arterioles less than 170 microns in diameter and venules less than 150 microns in diameter), and 7 +/- 7% of resistance resided in veins (distal to 150 microns). There was a significant redistribution (P less than 0.05) of resistance in all vessel classes after dipyridamole: coronary arteries constituted 42 +/- 6%, microvessels contained 27 +/- 5%, and veins had 31 +/- 8% of total coronary resistance. During control conditions, vascular resistance in coronary arteries and microvessels was 17 +/- 4 and 45 +/- 6 mmHg.min.g.ml-1, respectively. During vasodilation, resistance was significantly reduced (P less than 0.05) in both the arterial and microvessel segments to 6 +/- 2 and 4 +/- 2 mmHg.min.g.ml-1, respectively. Venous resistance was not significantly affected during dipyridamole-induced vasodilation. In conclusion, there was a marked reduction of coronary vascular resistance in response to dipyridamole, with the major component accounted for by dilation of microvessels.(ABSTRACT TRUNCATED AT 250 WORDS)
Chilian
W M
WM
Department of Medical Physiology, College of Medicine, Texas A&M University, College Station 77843.
Layne
S M
SM
Klausner
E C
EC
Eastham
C L
CL
Marcus
M L
ML
D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D001160:Arterioles / Q000187:drug effects / Q000502:physiology; D001794:Blood Pressure / Q000187:drug effects; D002245:Carbon Dioxide / Q000097:blood; D002415:Cats; D003326:Coronary Circulation / Q000187:drug effects*; D003971:Diastole / Q000187:drug effects; D004176:Dipyridamole / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects; D008833:Microcirculation / Q000187:drug effects; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D012016:Reference Values; D013599:Systole / Q000187:drug effects; D014655:Vascular Resistance / Q000187:drug effects*; D014664:Vasodilation; D014699:Venules / Q000187:drug effects / Q000502:physiology
D002245:Carbon Dioxide; D004176:Dipyridamole; D010100:Oxygen