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Effect of infused adenosine on cardiac output and systemic resistance in normal subjects.

1. The purine nucleoside adenosine relaxes smooth muscle in vitro and is a vasodilator in animals, but its effects on cardiac output and systemic vascular resistance have not been measured in normal conscious human subjects. 2. We have studied the effects of infused adenosine in doses of 0.005, 0.03 and 0.07 mg kg-1 min-1 on pulmonary blood flow and systemic vascular resistance in eight healthy volunteers, using a non-invasive, inert gas method and mass spectrometry. 3. At a dose of 0.07 mg kg-1 min-1, there was a rise in effective pulmonary blood flow (which is approximately equivalent to cardiac output) of 0.52 +/- 0.08 l min-1 m-2 (mean +/- s.e. mean) and a fall in estimated systemic vascular resistance of 357 +/- 44 dyn s cm-5. Despite this marked systemic vasodilation, there was no significant change in mean heart rate. 4. The effects of this dose of adenosine were maximal 2 min after starting the infusion, and had disappeared within 5 min of stopping it. 5. Adenosine may be therapeutically useful in the reduction of left ventricular afterload, where the absence of reflex tachycardia may be advantageous. We suggest that adenosine in doses of 0.03 mg kg-1 min-1 should be evaluated as a selective pulmonary vasodilator.