Selective and non-selective beta-adrenoreceptor blockade in the human forearm.

1. The immediate effects of selective (Pl) and non-selective (pl + 2) Padrenoreceptor blockade on local blood flow and substrate exchange were studied in young male subjects at rest and during dynamic forearm exercise. After a control period of rest, exercise and recovery, atenolol (PI), propranolol (/31+2) or placebo was infused into the right brachial artery during a second period of rest, exercise and recovery. 2. Neither atenolol nor propranolol influenced forearm blood flow during exercise. Atenolol and propranolol reduced the increase in lactate release from the forearm during exercise by 39 and 34% respectively. Neither agent influenced oxygen and glucose uptake. Propranolol increased forearm uptake of free fatty acids during exercise by 135%. A concomitant fall in forearm respiratory quotient indicated an increased utilization of free fatty acids. Atenolol did not affect free fatty acids uptake or respiratory quotient. 3. Blockade of vascular P,-receptors does not seem to be important for the blood flow regulation during muscular exercise. Both selective and non-selective Padrenoreceptor blockade reduce the lactate release from exercising skeletal muscle, but appear to have different effects on fat metabolism.