ADJUSTMENT OF METABOLISM, CATECHOLAMINES AND BETA-ADRENOCEPTORS TO 90MIN OF CYCLE ERGOMETRY

Adrenaline infusion of 0.1 mu g.kg(-1).min(-1) in healthy volunteers r esults in an increase of hepatic glucose production, an increase of th e absolute number of occupied beta-adrenoceptors and specific changes in metabolism. To compare these effects with the changes induced by an endogenous catecholamine release, we investigated healthy volunteers during cycle ergometry. After fasting at least 14 h seven healthy subj ects exercised for 90 min at an intensity of 20% below their individua l anaerobic threshold. The rate of glucose production as well as the t urnover rates of alanine and leucine were calculated using stable isot ope tracers. High and low affinity beta-adrenergic binding sites on ly mphocytes were determined by an equilibrium binding assay with (-)125 Iodocyanopindolol. After 90 min of cycling the rate of appearance of g lucose increased significantly from means of 2.0 (SD0.2) to 2.65 (SD 0 .50) mg.kg(-1).min(-1) with unchanged blood concentrations of glucose and lactate. The flux of the amino acids alanine and leucine decreased significantly from means of 0.91 (SD 0.21) to 0.62 (SD 0.14) mg.kg(-1 ).min(-1) and from 0.40 (SD 0.05) to 0.32 (SD 0.04)mg.kg(-1).min(-1), respectively. The mean free fatty acid concentration increased signifi cantly from 0.65 (SD 0.33) to 1.27 (SD 0.45) nmol.l(-1) during the end urance trial. The increase of glucose turnover and the decrease of ami no acid flux point to a metabolic shift towards enhanced utilization o f free fatty acids. Adrenaline and noradrenaline concentrations showed a moderate but significant increase from means of 0.61 (SD 0.20) to 0 .99 (SD 0.36) nmol.l(-1) and from 2.27 (SD 0.75) to 3.46 (SD 0.38) nmo l.l(-1), respectively. The number of high affinity P-adrenergic bindin g sites per cell (beta-adrenoceptors) nearly doubled from 770 (SD 130) to 1490 (SD 150) during 90 min of cycling. The observed endogenous pl asma catecholamine concentrations were not sufficient to change signif icantly the relative receptor occupancy. This would seem to indicate t hat the aerobic exercise induced effects depended more on the absolute number of occupied beta-adrenoceptors than on their relative receptor occupancy. When compared to the results of the adrenaline infusion ex periment the increases of the hepatic glucose production and the incre ase of beta-adrenoceptors were very similar in both groups despite ten times higher adrenaline plasma concentrations in the infusion group. This would seem to indicate that beta-adrenoceptors mediated effects d o not correlate with catecholamine plasma concentrations.