THE EFFECT OF BETA-ADRENERGIC-BLOCKADE ON NONESTERIFIED FATTY-ACID UPTAKE OF EXERCISING SKELETAL-MUSCLE DURING ARM CRANKING

beta-Adrenoceptor blocking agents impair endurance exercise performanc e in healthy subjects and in patients with hypertension. A possible ex planation for the reduced exercise tolerance is a diminished availabil ity of plasma non-esterified fatty acids (NEFA) for energy production during exercise. This study investigated the effect of beta-adrenocept or blockade on NEFA uptake of exercising skeletal muscle at elevated b lood NEFA concentrations. In 11 healthy volunteers a triacylglycerol e mulsion was infused at increasing rate for 1 hour before and 1 hour du ring one-armed cranking exercise at 60 % W-peak with and without prior administration of the beta(1+2)-adrenoceptor blocking agent propranol ol (80 mg per os). Arteriovenous concentration differences of NEFA acr oss the active forearm were measured and forearm blood flow was estima ted using venous occlusion plethysmography. Heart rate a nd blood flow were significantly lower after propranolol (p < 0.05). Propranolol di d not affect arterial NEFA concentration, arteriovenous NEFA differenc e or NEFA flux significantly. Net NEFA uptake increased with increasin g arterial NEFA concentration or inflow in a similar manner with and w ithout prior propranolol administration. Therefore, the results do not support the hypothesis that beta-adrenergic activity plays a role in the regulation of active skeletal muscle NEFA uptake under the conditi ons studied.