Metabolic aspects and sympathetic effects in the obese subject undergoing exercise testing

An impaired plasma Epinephrine (E) and Norepinephrine (NE) response has been described in obese patients during physical exercise. Serum potassium level is influenced either by physical exercise or by the adrenergic system. We studied 12 young obese patients and 12 young controls, all without any cardio-respiratory disorders, who underwent a cycloergometric test with steps of 20 watts every four minutes until exhaustion. During the test we recorded serum potassium levels, E and NE, insulin, glucose and RQ to confirm or not the observation of the reduced adrenergic response in obese patients. During exercise, although both groups reached a not significantly different mean peak value of maximal activity, E and NE increased, more in the controls than in the obese subjects (at peak of exercise 221 +/- 44.1 vs 71 +/- 21.5 pg/ml respectively for E; 2035 +/- 164.8 vs 1141 +/- 313.7 pg/ml respectively for NE). RQ was constantly lower in the obese patients than in the normals both during and after the stress. In both groups potassium increased significantly, but the obese patients had a significantly lower increment at peak of activity when compared to the controls (delta K+: 0.52 +/- 0.11 vs 1.007 +/- 0.17 meq/l respectively, p < 0.05). Insulin and glucose had a behaviour in line with literature in both groups. The behaviour of potassium could be an index of a higher effect of beta-adrenergic system in obese patients than in normals despite the different increases of catecholamines in the two groups. This hypothesis may agree with the preferential metabolic use of fatty acids in our obese patients as indicated by RQ values.