Influence of prenatal nicotine exposure on postnatal development of breathing pattern.

To determine if prenatal nicotine exposure alters the postnatal development of the ventilatory pattern and the frequency and duration of apneas, we recorded respiratory airflow with head-out body plethysmography in awake neonates on postnatal days 1, 2, 6, 10, 14, and 18. Data from 12 nicotine-exposed animals were compared with data from 12 saline-exposed animals. Nicotine (6 mg/kg of nicotine tartrate per day) or saline exposure was induced by osmotic minipumps that were implanted subdermally on the fifth day of gestation in Sprague-Dawley Dams. Although both saline- and nicotine-exposed pups gained weight at the same rate throughout the studies, there were subtle differences in ventilatory indices between the two groups. Nicotine-exposed animals had a significantly higher breathing frequency on day 10, and a lower tidal volume on days 14 and 18. Although ventilation tended to be lower in the nicotine-exposed animals, the difference was not significant. There was a significantly higher frequency of apneas in the nicotine-exposed compared with the saline-exposed animals on postnatal days 1 and 2, but the apnea duration did not differ between the groups. No apneas were observed in any of the animals after the sixth postnatal day. Prenatal nicotine exposure is associated with a greater incidence of apneas on the first two postnatal days, and then an altered breathing pattern that manifests at a later stage of development.