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1 Cardiovascular Centre,
Continuous release of nitric oxide contributes
to the maintenance of resting tone in the human forearm and coronary
circulations; however, evidence for a similar role of vasodilator
prostanoids such as prostacyclin is lacking. We examined whether
continuous release of prostacyclin contributes to basal forearm blood
flow. Flow was measured using venous occlusion plethysmography in 38 healthy volunteers [mean age 21.3 ± 2.5 yr (±SD); 13 female, 25 male] at rest, after administration of three
incremental intra-arterial infusions of either the cyclooxygenase
inhibitor aspirin or placebo, and before and after administration of
the endothelium-dependent and -independent dilators acetylcholine (30 µg/min) and nitroprusside (1 µg/min). To assess the effect of
aspirin on the production of prostacyclin, plasma 6-keto prostaglandin
F1
(6-keto-PGF1
; the stable
metabolite of prostacyclin) was measured by simultaneous arterial and
venous sampling. Aspirin produced a time- and dose-dependent reduction
in forearm blood flow, resulting in a 32% decrease at the highest
dose. The effect was maximal after 10 min. Flow at rest and after
aspirin doses of 1, 3, and 10 mg/min was 2.6 ± 0.2, 2.3 ± 0.2, 2.1 ± 0.2, and 1.8 ± 0.2 ml · 100 ml forearm
tissue
1 · min
1,
respectively (means ± SE, P < 0.001). Commensurate with these data, the net forearm
production of 6-keto-PGF1
was
52.9 ± 16.4, 11.7 ± 8.6, 18.7 ± 8.5, and 12.0 ± 12.5 pg · 100 ml forearm tissue
1 · min
1 for the respective
doses (P = 0.04). No time-dependent
reduction in flow was seen in subjects with vehicle infusion. Aspirin
did not affect the responses to acetylcholine or nitroprusside. These data suggest that continuous release of prostacyclin plays a role in
the maintenance of resting forearm blood flow. There appears to be a
direct link between the reduction in flow with aspirin and inhibition
of prostacyclin production.
aspirin; eicosanoids; vasodilation; vasoconstriction; regional blood flow
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