Physiological and symptomatic responses to postural change in non-diabetic subjects during hypoglycaemia

1. Insulin-induced hypoglycaemia is characterized by an autonomic disturbance which produces some of the symptoms of hypoglycaemia. How an additional autonomic stress like postural change may alter physiological responses and symptoms of hypoglycaemia is not known. In 10 healthy male subjects (mean age 24 years) we observed physiological and symptomatic responses to postural change during acute (20 min) and prolonged (60 min) hyperinsulinaemic (60 m-units min-1 m-2) hypoglycaemia (2.5 mmol/l) and euglycaemia (4.5 mmol/l), and placebo control (saline). 2. In all studies standing increased plasma catecholamines (adrenaline, P < 0.001; noradrenaline, P < 0.0001), blood pressure (P < 0.0001) and heart rate (P < 0.0001). Catecholamine responses to standing were augmented by acute hypoglycaemia (adrenaline, P < 0.005; noradrenaline, P < 0.01), but less so by prolonged hypoglycaemia (adrenaline, P < 0.05; noradrenaline, P < 0.05). Supine heart rate was higher before standing during prolonged hypoglycaemia (P < 0.05), but did not increase as much on standing when compared with acute hypoglycaemia and prolonged euglycaemia. 3. During acute hypoglycaemia, autonomic symptoms increased on standing, but during prolonged hypoglycaemia, in the presence of generally higher symptom scores, standing had no effect. Autonomic symptoms, with the exception of hunger, tended to decrease with time (P < 0.05) during prolonged hypoglycaemia. 4. To conclude, posture does modify the catecholamine and symptomatic responses to hypoglycaemia, but this effect is dependent on the duration of hypoglycaemia. Hypoglycaemia and hyperinsulinaemia had little or no effect on the cardiovascular responses to changing posture.