Influence of sympathetic nervous system on hypoglycaemic warning symptoms

The effect of mild insulin-induced hypoglycaemia on symptoms, physiological changes, and adrenaline responses was assessed in 10 normal subjects and 15 insulin-dependent diabetic patients (5 with reduced awareness of hypoglycaemic symptoms). When blood glucose was maintained at 3.2 mmol/l, reaction time was prolonged in both normal and diabetic subjects and plasma adrenaline levels increased in the normals and some diabetics; there were no other physiological responses. 2 normals and 1 diabetic were aware that their blood glucose was low. When blood glucose was maintained at 2.5 mmol/l for 30 min, 9/10 normals but only 4/15 diabetics recognised hypoglycaemia. Increases in hypoglycaemic symptom score, tremor, and sweating, and falls in diastolic blood pressure were significant only in the normal subjects and the 4 "aware" patients. Adrenaline levels increased in all cases, but were more pronounced in the normals and aware diabetics. Reaction time remained prolonged in all groups. All measurements returned to baseline when blood glucose was raised to 4.5 mmol/l. Impairments in adrenaline response may be common, even in diabetic patients without autonomic neuropathy and in those who do not complain of hypoglycaemic unawareness; consequent failure to recognise a falling blood glucose may predispose to a risk of severe hypoglycaemia.