Blood sugar, serum insulin and serum non-esterified fatty acid levels during thiopentone anaesthesia in dogs.

The purpose of this study was to determine the effect of thiopentone anaesthesia on glucose metabolism. Blood sugar (BS), serum immunoreactive insulin (IRI) and serum non-esterified fatty acid (NEFA) concentrations were measured during the course of (1) an intravenous glucose tolerance test (IVGTT), and (2) an intravenous insulin test (ITT), in conscious and anaesthetized fasted dogs. The IVGTTs were repeated in dogs under alpha- or beta-adrenergic blockade, induced by phentolamine or propranolol. During the IVGTT, the anaesthetized dogs showed glucose intolerance (blood sugar levels were higher than in the control group) and little serum IRI response to hyperglycaemia was detected. An attenuated initial decrease and a slower rebound of NEFA concentration was observed in anaesthetized animals than in controls. Phentolamine administration (5 mg.kg-1 iv) partly restored the IRI response without affecting the BS levels; propanolol (1 mg.kg-1 iv) had no effect. Anaesthetized dogs showed a moderate resistance to insulin induced hypoglycaemic action and a lack of serum NEFA response during counter-regulation of hypoglycaemia, while in conscious controls an intense rebound was observed. Hyperinsulinaemia after iv insulin administration was longer in anaesthetized dogs than in controls. The insulin distribution space was 78% of body weight and insulin t1/2 in blood group compared with 54% and 16 min, in controls. We conclude that thiopentone provokes disturbances in glucose and serum NEFA metabolisms and abolishes the serum IRI response to hyperglycaemia. These effects are influenced by extrapancreatic factors regulating serum IRI levels and by an alpha-adrenergic mechanism, via the inhibition of insulin secretion.