Fetal responses to acute maternal cocaine injection in sheep

Maternal cocaine abuse has been associated with neonatal neurological and neurobehavioral problems of unknown pathogenesis. We administered a single intravenous dose of cocaine (2 mg/kg) to 12 unanesthetized pregnant sheep; their fetuses had been catheterized in utero 2 days before the study. We measured fetal cerebral blood flow (CBF), cerebral metabolic rate of O₂ (CMR(O₂)), mean arterial blood pressure (MAP), and blood gases before and 2, 5, 15, and 30 min after maternal cocaine injection. Fetal CBF increased by 37 ± 33% (mean ± SD) at 5 min and returned to baseline by 15 min. Regional brain blood flow changes paralleled CBF changes with the greatest increases occurring in cerebellum (54 ± 43%) and brain stem (54 ± 52%). Cerebral vascular resistance was decreased for cerebellum (22%) and brain stem (19%) but was unchanged for cerebral hemispheres and caudate. Increased CBF at 5 min was associated with a 20 ± 9% increase in fetal MAP and a 38 ± 13% decrease in fetal arterial O₂ content. Fetal CMR(O₂) was unchanged. There was a decrease in fetal intestinal blood flow at 2 min, an increase in myocardial, adrenal, and renal blood flow at 5 min, and no change in placental blood flow. Maternal cocaine injection causes fetal hypoxemia, hypertension, and increased CBF. Possible mechanisms for cerebral vasodilation (in some areas) include hypoxemia, impaired autoregulatory response to increased blood pressure, and/or direct or indirect vascular effects of cocaine or its metabolites.