Central hyperglycaemic effect of adrenaline and carbachol

The effect of chemical stimulation of the brain on glucoregulation was studied in anaesthetized rats. Adrenaline, noradrenaline, acetylcholine, dopamine and carbachol (5 X 10(-8) mol/microliter saline) were injected directly into the third cerebral ventricle and changes in hepatic venous plasma glucose, immunoreactive glucagon and insulin concentrations were studied. The injection of adrenaline and carbachol into the third cerebral ventricle resulted in a marked hyperglycaemia associated with increased immunoreactive glucagon. Adrenaline-induced hyperglycaemia was not affected by bilateral adrenalectomy, while carbachol-induced hyperglycaemia was completely inhibited by adrenalectomy. The injection of somatostatin (1 X 10(-9) mol) with adrenaline into the third cerebral ventricle did not influence adrenaline-induced hyperglycaemia, while carbachol-induced hyperglycaemia was inhibited by co-administration with somatostatin. These results suggest that adrenergic and cholinergic neurons in the central nervous system may increase hepatic glucose output by different mechanism.