Potent mental stress and insulin absorption in normal subjects

Effects of mental stress (a 20-min modified Stroop's color-word conflict test; CWT) on the absorption of 125I-labeled soluble human insulin (10 U s.c. in the thigh 60 min before CWT) and on subcutaneous adipose tissue blood flow (ATBF; 133Xe clearance); heart rate (HR); arterial blood pressure (BP); and arterial levels of epinephrine (Epi), norepinephrine (NE), and glycerol were studied in 11 healthy subjects. Insulin absorption was measured as elimination of radioactivity (external gamma-counting) and as appearance of plasma immunoreactive insulin (IRI). The glucose-clamp technique was used to maintain normoglycemia. Identical measurements were performed during a control day without CWT. HR and mean BP increased markedly (35 +/- 5 beats/min and 30 +/- 3 mmHg) during CWT despite only minor elevations in plasma catecholamines. Thus, arterial plasma Epi rose from 0.18 +/- 0.03 to 0.82 +/- 0.17 nM (P less than .01) and NE from 0.94 +/- 0.09 to 1.69 +/- 0.18 nM (P less than .001). ATBF showed a biphasic response, with a 100% elevation during CWT followed by a decrease and a second peak of similar magnitude approximately 0.5 to 1 h after CWT. Blood glycerol was approximately doubled during CWT and remained elevated during recovery. Despite these changes, insulin absorption was unaltered during and after stress. Thus, elimination rates of 125I, plasma IRI levels, and amounts of glucose needed to maintain normoglycemia were all similar during the stress and control days. These results suggest that absorption of soluble insulin from subcutaneous injection sites in the thigh is unaltered during potent mental stress in healthy subjects despite a considerable and prolonged increase in ATBF.