Attenuation of forearm vasodilator responses to mental stress by regional beta-blockade, but not by atropine.

Forearm blood flow during mental stress (Stroop's colour word conflict test) was studied in 18 healthy men before and during regional beta-adrenoceptor blockade (propranolol 0.5 mg), muscarinic receptor blockade (atropine 0.2 mg) and combined blockade, and compared with results obtained in untreated controls. Forearm blood flow was measured with venous occlusion plethysmography, and forearm vascular resistance was calculated. Arterial and venous blood sampling was performed for determination of adrenaline and noradrenaline in plasma. Mental stress increased heart rate, systolic and diastolic blood pressures and forearm blood flow, and lowered the forearm vascular resistance, to the same degree as in our previously studied controls. Neither of the intra-arterially administered drugs had any discernible systemic effects. Beta-blockade increased forearm vascular resistance by 32% and decreased forearm blood flow by 21% compared with unblocked levels during mental stress, whereas forearm vasodilation was maintained throughout the stress test in the control group (P < 0.05). Intra-arterial atropine had no certain effects. Arterial adrenaline levels during mental stress were similar in the receptor-blocked and control groups. In conclusion, the sustained forearm vasodilation during mental stress appears to be partly mediated via beta 2-adrenoceptor stimulation (i.e. by adrenaline), but we obtained no support for a cholinergic vasodilating mechanism.