Threshold levels of maternal nicotine impairing protective responses of newborn rats to intermittent hypoxia

Experiments were carried out to determine the threshold level of maternal n icotine that impairs protective responses of rat pups to hypoxia. From days 6 or 7 of gestation, pregnant rats received either vehicle or nicotine (1. 50, 3.00, or 6.00 mg of nicotine tartrate.kg body wt(-1).day(-1)) or vehicl e continuously via a subcutaneous osmotic minipump. On postnatal days 5 or 6, pups were exposed to a single period of hypoxia produced by breathing an anoxic gas mixture (97% N-2 or 3% CO2) and their time to last gasp was det ermined, or they were exposed to intermittent hypoxia and their ability to autoresuscitate from hypoxic-induced primary apnea was determined. Perinata l exposure to nicotine did not alter the time to last gasp or the total num ber of gasps when the pups were exposed to a single period of hypoxia. The number of successful autoresuscitations on repeated exposure to hypoxia was , however, decreased in pups whose dams had received either 3.00 or 6.00 mg of nicotine tartrate/kg body wt; these dosage regimens produced maternal s erum nicotine concentrations of 19 +/- 6 and 35 +/- 8 ng/ml, respectively. Thus our experiments define the threshold level of maternal nicotine that s ignificantly impairs protective responses of 5- to 6-day-old rat pups to in termittent hypoxia such as may occur in human infants during episodes of pr olonged sleep apnea or positional asphyxia.