Hyperoxia blunts counterregulation during hypoglycaemia in humans: possible role for the carotid bodies?

Chemoreceptors in the carotid bodies sense arterial oxygen tension and regulate respiration. Isolated carotid body glomus cells also sense glucose, and animal studies have shown the carotid bodies play a role in the counterregulatory response to hypoglycaemia. Thus, we hypothesized that glucose infusion rate would be augmented and neuro-hormonal counterregulation blunted during hypoglycaemia when the carotid bodies were desensitized by hyperoxia. Seven healthy adults (four male, three female) underwent two 180 min hyperinsulinaemic (2 mU (kg fat-free mass (FFM))(-1) min(-1)), hypoglycaemic (3.33 mmol l(-1)) clamps 1 week apart, randomized to either normoxia (arterial P-o2 (P-aO2) 111 +/- 6.3 mmHg) or hyperoxia (P-aO2, 345 +/- 80.6 mmHg) (P < 0.05). Plasma glucose concentrations were similar during normoxia and hyperoxia at baseline (5.52 +/- 0.15 vs. 5.55 +/- 0.13 mu mol ml(-1)) and during the clamp (3.4 +/- 0.05 vs. 3.3 +/- 0.05 mu mol ml(-1)). The glucose infusion rate was 44.2 +/- 3.5% higher (P < 0.01) during hyperoxia than normoxia at steady state during the clamp (28.2 +/- 0.15 vs. 42.7 +/- 0.65 mu mol (kg FFM)(-1) min(-1); P < 0.01). Area under the curve values (expressed as percentage normoxia response) for counterregulatory hormones during hypoglycaemia were significantly suppressed by hyperoxia (noradrenaline 50.7 +/- 5.2%, adrenaline 62.6 +/- 3.3%, cortisol 63.2 +/- 2.1%, growth hormone 53.1 +/- 2.7%, glucagon 48.6 +/- 2.1%, all P < 0.05 vs. normoxia). These data support the idea that the carotid bodies respond to glucose and play a role in the counterregulatory response to hypoglycaemia in humans.