THE EFFECT OF ADRENERGIC RECEPTOR BLOCKADE ON PLASMA INSULIN CONCENTRATIONS DURING EXERCISE

Abstract

805 The purpose of this study was to test the hypothesis that the decrease in plasma insulin concentrations during exercise is mediated via α-2 receptors. In eight males (25 ± 1 yr., 73 ± 2 kg) we measured plasma insulin (INS) and glucose (GLU) concentrations before and during 60-min ergometer (60-70% VO2max) bicycle exercise. Subjects were studied with (α-1 (Prazosin 1mg) or α-2 (Yohimbine 15mg)) and without (control experiments (CO)) adrenergic blockade. During CO and α-1 blockade, INS always decreased (from 18 ± 1 and 21 ± 1 to 6 ± 1 and 9 ± 1 pM (at t = 60 min), CO and α-1, respectively). The decrease was similar in CO (−11 ± 1 pM) and α-1 (−12 ± pM) experiments (P>0.05). In contrast, during exercise with α-2 blockade, INS increased from 18 ± 1 to 25 ± 1 pM (P<0.05) in the first 20 min, after which INS decreased (to 13 ± 1 pM (at t = 60 min)). At the end of exercise, INS were higher (P<0.05) and the change from before exercise less (P<0.05) in experiments with α-2 blockade compared with CO and α-1 blockade. At the end of exercise GLU was decreased (P<0.05) during CO and α-2 blockade (−0.36 ± 0.04 mM (pooled data)). During α-1 blockade GLU increased (+0.79 ± 0.08 mM (P<0.05)) in the first 30 min but returned to pre-exercise concentrations at the end of exercise. These data suggest: 1) The exercise induced decrease in plasma insulin concentrations is mediated via α-2, but not α-1, receptors located on the pancreatic β-cells. 2) Plasma insulin concentrations during exercise are not influenced by the prevailing plasma glucose concentration.