Endocrine Abstracts

Alteration of sympathetic nervous system (SNS) activity may be involved in the development of obesity. Among stimuli which may activate the SNS, stress is often quoted. Responses to stressors include stimulation of the hypothalamo-pituitary-adrenal axis (HPA) and of the SNS, which result in increased plasma cortisol and catecholamines concentrations. Although the stress response seems to be automatic (therefore not subject to regulation), studies in human have highlighted the heterogeneity of the cortisol response, leading to the differentiation of 2 subgroups of high- and low- stress responders. Although this distinction is well documented for the cortisol response, it is less known whether epinephrine and norepinephrine stimulation follows the same distribution. Therefore we decided to evaluate the variability of catecholamine responses to different stimuli, ie. hypoglycemia and mental stress, in 8 healthy volunteers. A 2 steps hypoglycemia (30 minutes at 4 mM, 30 min at 3 mM) was obtained by continuous infusion of human insulin (actrapid HM 100). Mental stress consisted in a 30 min session of arithmetic’ and Stroop task. Epinephrine and norepinephrine were measured by HPLC. As already documented, hypoglycemia provoked mainly an epinephrine release (+794±125%) while mental stress essentially produced a norepinephrine release (+70±10%). There were considerable interindividual variations in these responses (epinephrine response to hypoglycemia: 294–1147% norepinephrine response to mental stress 33–108%). The peak concentration of plasma epinephrine during hypoglycemia was positively correlated to the peak plasma norepinephrine concentration during mental stress: r=0.499, P<0.05, (Spearman rank test). The observation that the same individuals who rise a large response to mental stress also respond markedly to hypoglycemia support the concept of high and low SNS responders. The mechanisms underlying these interindividual variations (genetic or acquired), and the possible consequences of high SNS responses on the development of cardiovascular or metabolic disorders remain to be evaluated.