Age-independent forearm vasodilatation by acetylcholine and adenosine 5'-triphosphate in humans.

1. Forearm vasodilator responses to acetylcholine, ATP and sodium nitroprusside were examined in healthy young (20 +/- 1 years, n = 9), middle-aged (46 +/- 2 years, n = 6) and old (57 +/- 1 years, n = 6) subjects. 2. A brachial artery was cannulated with a 20-gauge cannula through which drugs at graded doses were locally infused for 2 min at each dose. During drug infusions, forearm blood flow was continuously measured at 15 s intervals using a plethysmograph. Forearm vascular resistance was calculated from forearm blood flow and mean blood pressure obtained in the opposite arm. Basal forearm blood flow and forearm vascular resistance did not differ between the three groups. 3. Acetylcholine and ATP were used to examine endothelium-dependent vasodilatation, and sodium nitroprusside was used to examine endothelium-independent vasodilatation. All three drugs caused dose-dependent increases in forearm blood flow (P less than 0.01) and decreases in forearm vascular resistance (P less than 0.01). The increases in forearm blood flow or decreases in forearm vascular resistance in response to infusions of the three drugs did not differ between the three groups. 4. These results suggest that endothelium-dependent and endothelium-independent vasodilatation in forearm resistance arteries do not alter with ageing in humans.