Autonomic neural control mechanisms of substrate and hormonal responses to acute hypoglycaemia in man

The contributions of adrenergic and cholinergic mechanisms to recovery from acute hypoglycaemia induced by insulin (0.15 units/kg i.v.) were examined in eleven normal subjects, six subjects with a pre-ganglionic sympathectomy (adrenergic denervation) and six sympathectomized subjects given atropine (combined adrenergic denervation and cholinergic blockade). Blood glucose recovery was impaired only in the sympathectomized subjects given atropine. The blood lactate response was reduced and the rise in free fatty acids was delayed in both groups of sympathectomized subjects, in whom the normal rises of plasma cyclic AMP and noradrenaline were absent. The plasma pancreatic glucagon response was appropriate to the prevailing blood glucose concentrations in all three groups. The cortisol response was impaired and the pattern of ACTH secretion was abnormal in sympathectomized subjects given atropine. Growth hormone levels were higher in both sympathectomized groups. Blood glucose homeostasis was impaired during combined adrenergic denervation and cholinergic blockade. Glucagon secretion was activated independently of vagal control. In the sympathectomized group given atropine, the rise in plasma cortisol was blunted despite a greater degree of hypoglycaemia. A blockade of central cholinergic receptors producing impaired activation of ACTH secretion at hypothalamic level may explain, at least in part, this delayed restoration of normoglycaemia.