The effect of beta adrenergic receptor blockade on the vasodilator response in the forearm to voluntary hyperventilation.

1. Blood flow was simultaneously measured by venous-occlusion plethysmography in both forearms of ten healthy men. 2. Voluntary overbreathing to produce about 8 times the resting ventilation caused a vasodilatation similar in both forearms. 3. When one forearm was treated with an intra-arterialinfusion of propranolol, a beta adrenergic blocking agent, the vasodilator response was reduced by an average of 28%, the reduction was significant (P < 0-01). 4. The failure of propranolol to abolish the vasodilator response was not due to incomplete block of beta adrenergic receptors since the dose of propranolol used reversed the vasodilator response to an intravenous infusion of adrenaline. 5. The results suggest that the vasodilator response to voluntary hyperventilation can be explained partly, but not entirely, by the release to the circulation of an adrenaline-like substance.