Despite causing sympathetic activation, prolonged hypoglycaemia produces little change in HR (heart rate) in healthy young adults. One explanation could be concurrent parasympathetic activation, resulting in unchanged net effects of autonomic influences. In the present study, hypoglycaemic (2.7 mmol/l) and normoglycaemic (4.7 mmol/l) hyperinsulinaemic clamp studies were performed after normoglycaemic baseline clamp periods with 15 healthy volunteers (seven male; mean age, 27 years) on two occasions in a randomized single-blind cross-over design. Non-invasive indices of cardiac autonomic activity and hormones were measured at baseline and 1 h after the beginning of hypoglycaemia or control normoglycaemia. Plasma insulin levels and mean HR were similar during both conditions. During hypoglycaemia, there was a 485% increase in plasma adrenaline (epinephrine). A shortening of the pre-ejection period by 45% suggested strong sympathetic cardiac activation. High-frequency (0.15–0.45 Hz) HRV (HR variability) increased, indicating a concomitant increase in parasympathetic tone. Thus, during hypoglycaemia-induced sympathetic cardiac activation in healthy adults, parasympathetic mechanisms are involved in stabilizing mean HR.

1. The effects of intravenous infusions of recombinant human insulin-like growth factor 1 and insulin on palmitate kinetics, lipolysis and on serum triacylglycerol were compared. Overnight-fasted normal subjects received high doses of insulin-like growth factor I (30 μgh −1 kg −1 ) and insulin (0.23 nmol h −1 kg −1 ; group 1), low doses of insulin-like growth factor I (5 μg h −1 kg −1 ) and insulin (0.04 nmol h −1 kg −1 ; group 2) or saline (control group). The doses of insulin-like growth factor I and insulin were equipotent with regard to increases in glucose uptake during 8 h euglycaemic clamping. 2. Whole-body palmitate flux (measured by continuous infusions of [2,2-D 2 ]palmitate) was lowered dose-dependently by 68% ± 6% during insulin-like growth factor I and by 82% ± 2% during insulin after 8 h of infusions of high doses (insulin-like growth factor I versus insulin; not significant). Plasma palmitate, glycerol and triacylglycerol concentrations had decreased to a similar extent at the end of the infusions of both peptides at either dose. 3. The present results demonstrate that insulin-like growth factor I and insulin infused at doses which result in identical increases in glucose uptake during euglycaemic clamping are equipotent inhibitors of lipolysis.