Effects of hyperinsulinemia on sympathetic responses to mental stress

In a recent study, we could not find evidence to support the hypothesis tha t insulin activates the sympathetic nervous system (SNS) during a hyperinsu linemic glucose clamp procedure. Mental stress tests (MST), however, may be used to detect differences in blood pressure and SNS activity that; are no t present during baseline or resting conditions. In this study, we aimed to investigate the effects of hyperinsulinemia during glucose clamp on blood pressure and sympathetic responses to mental stress. Borderline hypertensiv e but otherwise healthy 21-year-old men (n = 18) underwent 5 min of mental arithmetic stress testing (MST-I) before and at the end of 120 min of isogl ycemic hyperinsulinemic glucose clamp (MST-2) with infusion rates of glucos e and insulin kept constant. Insulin concentration increased from 119 +/- 1 0 pmol/L to 752 +/- 65 pmol/L. We observed highly significant increases in blood pressure and heart rate in response to MST, but neither insulin nor s aline solution infusions affected these responses. During MST-1, norepineph rine increased by 461 +/- 165 pmol/L (mean +/- SEM) and epinephrine by 218 +/- 76 pmol/L, During MST-2 the changes were 372 +/- 112 pmol/L and 187 +/- 60 pmol/L, respectively. The norepinephrine (P = .8) and epinephrine (P = .7) responses were unchanged by insulin. Thus, there were similar increases in blood pressure, heart rate, and plasma catecholamine concentrations in arterialized venous blood in response to MST despite the infusion of insuli n. A possible time effect was excluded by including a saline solution contr ol group (n = 7) that showed almost identical results. Our results suggest that acute hyperinsulinemia during isoglycemic glucose clamp does not interfere with cardiovascular or sympathetic responses to me ntal stress, (C) 2000 American Journal of Hypertension, Ltd.