Recently, investigators have reported an alteration of postnatal
respiratory pattern, deficient hypoxic arousal from sleep,
and an increased incidence of sudden infant death syndrome
(SIDS) among human infants exposed to cocaine prenatally,
thus suggesting that prenatal cocaine exposure may perturb
the maturation of respiratory control thereby increasing the
risk for SIDS. To investigate the effects of prenatal cocaine on
postnatal respiration, we evaluated the ventilatory response to
0.21 F(I)O(2) (baseline) and at 0.15, 0.10, and 0.08 F(I)O(2) by the
barometric method on days 4-5 of life in 23 New Zealand
White rabbit pups born to cocaine-exposed (30 mg/kg/day of
cocaine HCl by continuous subcutaneous infusion), pair-fed
and free-fed does. The chamber pressure deflection (proportional
to V(T) after appropriate calculation) was computer-sampled
at 200 Hz when the unanesthetized pups were resting
quietly with no gross body movements. Recording was made
after 10 min acclimatization to a specific F(I)O(2). We found that
baseline ventilation did not differ significantly among study
groups. However, minute ventilation (V̇(I)), inspiratory flow
(V(T)/T(I)), tidal volume (V(T)), increased significantly with hypoxia
to peak values at 0.08 F(I)O(2) in pair-fed and free-fed pups
but these measurements did not increase significantly in
cocaine-exposed pups. Our finding of a deficient second phase
of the hypoxic ventilatory response among cocaine-exposed
pups supports the hypothesis that prenatal cocaine perturbs
the maturation of respiratory control. It is likely that manipulation
of dose, gestational timing, and route of prenatal
cocaine exposure in an animal model will provide a useful tool
to probe the maturation of control of breathing and potentially
the pathogenic origin of SIDS.