The cardiorespiratory response to anoxia: normal development and the effect of nicotine

Maternal smoking increases the risk of the sudden infant death syndrome (SIDS) 2-4-fold. The mechanism is unknown but may be related to hypoxia responses. Recovery from hypoxic apnea by young mammals depends on gasping and bradycardia. We asked whether prenatal nicotine exposure, reported to reduce hypoxic survival in 2 day old rat pups, acted by impairing gasping or bradycardia. Pregnant rats were infused throughout gestation and 1 week postnatally with nicotine tartrate (NIC) 12 mg/kg per day or saline (CON). Maternal plasma nicotine was 134.4 +/- 42 ng/ml, significantly reducing pup body weight. Pups at 3-28 days were exposed to anoxia (97% N2/3% CO2) until gasping ceased, while breathing and heart rate were recorded. NIC and CON groups were not significantly different at any age, in baseline heart rate, respiratory rate, the time course for bradycardia, time to gasp onset, duration of gasping, or number of gasps, although most of these variables declined significantly with age. We conclude that responses to anoxia are not affected by prenatal high-dose nicotine.