MENTAL STRESS INCREASES GLUCOSE-UPTAKE DURING HYPERINSULINEMIA - ASSOCIATIONS WITH SYMPATHETIC AND CARDIOVASCULAR RESPONSIVENESS

Infusion of epinephrine and norepinephrine reduces insulin-mediated gl ucose disposal, ie, induces insulin resistance. Mental stress increase s concentrations of both plasma catecholamines. However, the effect of acute mental stress on insulin-mediated glucose uptake has not been e xamined. We observed in pilot studies that a mental stress test (MST) during a euglycemic glucose clamp decreased blood glucose concentratio n. In a prospective study, euglycemic hyperinsulinemia was established during 120 minutes of glucose clamping; the subjects (N = 74) then un derwent 5 minutes of intense mental arithmetics with infusion rates of glucose and insulin kept constant. During MST. plasma epinephrine and norepinephrine increased (by 0.23 +/- 0.02 and 0.50 +/- 0.05 nmol/L) together with blood pressure ([BP] by 18 +/- 8/9 +/- 1 mm Hg) and hear t rate ([HR] by 21 +/- 1 beats per minute), with P less than .0001 for all changes. During mental stress, blood glucose concentration decrea sed by 0.4 +/- 0.1 mmmol/L (P<0.0001), followed by full recovery after another 10 minutes. Serum insulin was unchanged. indicating an acute hut transient increase in glucose uptake. This finding was unrelated t o age, sex, body mass, and BP status. Fifty-nine subjects with a decre ase in glucose concentrations during MST were characterized by accentu ated epinephrine response to MST (a change of 0.25 +/- 0.03 v 0.12 + 0 .02 nmol/L, P=.001), increase in systolic BP (by 20 +/- 2 v 10 +/- 3 m m Hg, P=.008), and increase in HR (by 23 +/- 2 v 15 +/- 2 beats per mi nute, P=.008) as compared with 15 subjects with unchanged/increased gl ucose concentration. Thus, when mental stress is applied while insulin -mediated glucose uptake is already stimulated, sympathetic overactivi ty is initially accompanied by increased glucose uptake. This finding is unexpected and cannot be fully explained. The increase in skeletal muscle blood flow during mental stress, with increased substrate deliv ery to the metabolically active muscle cells, or other unknown interac tions between insulin and the sympathetic nervous system (SNS) may exp lain the observation. Copyright (C) 1995 by W.B. Saunders Company