Endothelium-dependent and -independent perfusion reserve and the effect of L-arginine on myocardial perfusion in patients with syndrome X.
BACKGROUND
Impaired vasodilatation capacity in patients with angina pectoris and a normal coronary arteriogram (syndrome X [SX]) has been reported. Most studies report on the response in epicardial vessels. This does not necessarily reflect compromised myocardial microcirculation. Lack of the NO precursor L-arginine has been suggested as a possible cause.


RESULTS
Myocardial blood flow (MBF) was measured, using PET, at rest (MBF-rest) and during intravenous dipyridamole (MBF-DIP) in 25 women (mean age 53+/-7 years) with SX. Thirty healthy volunteers served as controls. One group (A) consisted of 15 age-matched female volunteers (54+/-10 years). The other control group consisted of 15 young healthy women (B; 24+/-5 years). In 12 SX patients, MBF-rest and MBF during cold pressor testing were also measured after infusion of L-arginine (6.7 g/min for 45 minutes). The increase in MBF after cold pressor testing was similar in the SX group compared with controls. L-arginine did not affect MBF-rest (0.83+/-0.14 versus 0.89+/-0.13 mL. g-1. min-1) or MBF after cold pressor test (0.95+/-0.10 versus 1. 03+/-0.17 mL. g-1min-1). In contrast, the hyperemic response to DIP was blunted compared with the group A controls (1.68+/-0.49 versus 2. 34+/-0.45 mL. g-1. min-1, P<0.05); this resulted in a significant reduction of the coronary flow reserve in SX patients relative to controls (2.03+/-0.53 versus 2.96+/-0.63 mL. g-1. min-1, P<0.01).


CONCLUSIONS
In patients with SX, the microcirculatory response to cold, reflecting the endothelium function, is normal and unaltered by intravenous L-arginine. This suggests preserved microcirculatory endothelial function. However, a markedly attenuated hyperemic flow and flow reserve after DIP suggest a dysfunction of the adenosine-mediated endothelium-independent vasodilatation at the microcirculatory level in these patients.
Bøttcher
M
M
Department of Cardiology B, Aarhus University Hospital, Aarhus N, Denmark.
Botker
H E
HE
Sonne
H
H
Nielsen
T T
TT
Czernin
J
J
D001120:Arginine / Q000627:therapeutic use*; D001794:Blood Pressure / Q000502:physiology; D003080:Cold Temperature; D003326:Coronary Circulation / Q000187:drug effects*; D004176:Dipyridamole; D004730:Endothelium, Vascular / Q000503:physiopathology*; D005260:Female; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D008833:Microcirculation / Q000503:physiopathology; D017566:Microvascular Angina / Q000175:diagnosis / Q000000981:diagnostic imaging / Q000188:drug therapy* / Q000503:physiopathology*; D008875:Middle Aged; D012016:Reference Values; D014055:Tomography, Emission-Computed; D014655:Vascular Resistance / Q000187:drug effects; D014665:Vasodilator Agents
D014665:Vasodilator Agents; D004176:Dipyridamole; D001120:Arginine