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-a drenoceptor blockade (propranolol 0.5 mg), muscarinic receptor blockad e (atropine 0.2 mg) and combined blockade, and compared with results o btained in untreated controls. Forearm blood flow was measured with ve nous occlusion plethysmography, and forearm vascular resistance was ca lculated. Arterial and venous blood sampling was performed for determi nation of adrenaline and noradrenaline in plasma. Mental stress increa sed heart rate, systolic and diastolic blood pressures and forearm blo od flow, and lowered the forearm vascular resistance, to the same degr ee as in our previously studied controls. Neither of the intra-arteria lly administered drugs had any discernible systemic effects. Beta-bloc kade increased forearm vascular resistance by 32% and decreased forear m blood flow by 21% compared with unblocked levels during mental stres s, whereas forearm vasodilation was maintained throughout the stress t est in the control group (P < 0.05). Intra-arterial atropine had no ce rtain effects. Arterial adrenaline levels during mental stress were si milar in the receptor-blocked and control groups. in conclusion, the s ustained forearm vasodilation during mental stress appears to be partl y mediated via beta(2)-adrenoceptor stimulation (i.e. by adrenaline), but we obtained no support for a cholinergic vasodilating mechanism.