Effects of hyperglycemia on gasping and autoresuscitation in newborn rats

The aim of this study was to test the effects of glucose on the gasping ability and survival in a rat pup model during acute anoxia. Newborn rat pups of both 1 and 8 days of age were given glucose (30 and 60 mg/animal) or saline intraperitoneally and subsequently subjected to anoxia (100% N2). Glucose supplement induced hyperglycemia. Respiration was recorded by barometric plethysmography. The rat pups responded to acute anoxia with a robust sequence of respiratory pattern: hyperpnea, primary apnea, hypoxic gasping and secondary apnea. During anoxia the 1-day-old rats gasped much longer than the 8-day-old rats (23.4 +/- 1.0 vs. 6.1 +/- 0.5 min, p < 0.001). No difference was found in gasping duration between the saline control and the glucose-supplemented 1-day-old rat pups. The 8-day-old supplemented rats gasped much longer (9.3 +/- 0.5 min) than the control rats (6.1 +/- 0.5 min, p < 0.01). The animals autoresuscitated when they received oxygen (100%) during the gasping period. When oxygen was given after the gasping period, the survival rate was 33.3% in control and 0% in supplemented 1-day-old rats, and 100% in control and 50% in glucose-supplemented 8-day-old rats (p < 0.02). Further controlled experiments for a fixed period of anoxia to 13.5 min resulted in survival rates of 50.0% for controls and 28.6% for supplemented animals, respectively. The overall survival rate was then 85.2% in control and 52.9% in supplemented 8-day-old rats (p < 0.05). Lactate concentration in blood rapidly increased in the first 6 min of anoxia and thereafter gradually increased to 22.1 mmol/l around the last gasp in the 1-day-old rats. Hyperglycemia did not cause further accumulation of lactate despite a transient elevation over the control rats at 6 min of anoxia. In the 8-day-old supplemented animals the lactate level was only modestly increased, probably due to the prolonged gasping period. In conclusion, we found that gasping performance was well preserved in the 8-day-old glucose-supplemented rats, whereas the autoresuscitation mechanism after the last gasp might be altered due to hyperglycemia. In addition, the accumulation of lactate in the blood did not affect the gasping performance and the mechanisms of autoresuscitation.