The Effect of Beta-Adrenergic Blockade on Non-Esterified Fatty Acid Uptake of Exercising Skeletal Muscle During Arm Cranking

β-Adrenoceptor blocking agents impair endurance exercise performance in healthy subjects and in patients with hypertension. A possible explanation for the reduced exercise tolerance is a diminished availability of plasma non-esterified fatty acids (NEFA) for energy production during exercise. This study investigated the effect of β-adrenoceptor blockade on NEFA uptake of exercising skeletal muscle at elevated blood NEFA concentrations. In 11 healthy volunteers a triacylglycerol emulsion was infused at increasing rate fori hour before and 1 hour during one-armed cranking exercise at 60 % W_peak with and without prior administration of the β_{1 + 2}-adrenoceptor blocking agent propranolol (80 mg per os). Arteriovenous concentration differences of NEFA across the active forearm were measured and forearm blood flow was estimated using venous occlusion plethysmography. Heart rate and blood flow were significantly lower after propranolol (p < 0.05). Propranolol did not affect arterial NEFA concentration, arteriovenous NEFA difference or NEFA flux significantly. Net NEFA uptake increased with increasing arterial NEFA concentration or inflow in a similar manner with and without prior propranolol administration. Therefore, the results do not support the hypothesis that β-adrenergic activity plays a role in the regulation of active skeletal muscle NEFA uptake under the conditions studied.

Key words

β-Adrenoceptor blocking agents - armcranking - non-esterified fatty acids - skeletal muscle substrate fluxes - propranolol