Obese male subjects show increased resting forearm venous plasma noradrenaline concentration but decreased 24-hour sympathetic activity as evaluated by thrombocyte noradrenaline measurements

Abstract

OBJECTIVE: To study resting forearm venous plasma noradrenaline (NA) and 24 h sympathoadrenal activity evaluated by measurements of thrombocyte NA and adrenaline (A) in obese male subjects before and after weight reduction.

DESIGN: Blood samples were collected in obese subjects and in controls after an overnight fast.

MEASUREMENTS: Fatness and fat distribution parameters, plasma and thrombocyte NA and A, lymphocyte β β₂-adrenoceptor mRNA, cAMP and lymphocyte subset composition.

RESULTS: Forearm venous plasma NA at rest was significantly elevated in the obese subjects and correlated to the body mass index and diastolic blood pressure. Thrombocyte NA and A correlated, however, negatively to the body fat % in obese subjects. Further analysis showed that thrombocyte NA and A were reduced in obese subjects with body fat % above 40% but not in the other groups. Weight reduction normalized both forearm venous plasma NA and thrombocyte NA and A. ββ₂-adrenoceptor mRNA correlated positively to the frequency of CD3−CD56+ and CD3+CD8+ cells in the blood and negatively to plasma A, but there was no difference in the mRNA level, cyclic AMP and lymphocyte subset composition between obese and controls.

CONCLUSIONS: Sympathetic activity at rest as evaluated by forearm venous plasma NA was increased in the obese male subjects and this abnormality was related to the increase in body mass index and the arterial blood pressure. Thrombocyte NA and A, which is likely to reflect 24 h plasma catecholamine concentrations were reduced in obese subjects with a body fat % above 40%, probably due to a reduced physical activity in these subjects. Both catecholamine parameters were normalized by weight reduction.