Effect of nimodipine on newborn lamb cerebral blood flow

The effects of nimodipine, on total and regional cerebral blood flow and cardiovascular function of the newborn chloralose-anesthetized lamb were investigated following intravenous bolus infusions (0.2, 0.6 and 2.0 micrograms/kg). At 2.0 micrograms/kg, the mean arterial blood pressure increased from 72.3 to 85.8 mm Hg. Total cerebral blood flow 45 min after infusion increased by 93%, as did regional flows to the gray (101%) and white (77%) matter and subcortex (108%). In a separate series of experiments we decreased arterial blood pressure from 71 to 40 mm Hg by phlebotomy. Nimodipine (30 micrograms/kg) bolus infusion significantly increased blood flow above control values to the total brain (41%), gray matter (53%), subcortex (76%) and brainstem (69%) 10 and 40 min later. However, no further increase in flow or decrease in cerebrovascular resistance was observed when compared to hypotension alone. Nimodipine appears to be well tolerated in the newborn lamb, and appears to increase cerebral flow during normotension. At the levels of hypotension used in the current experiments, nimodipine produced no further increases in cerebral blood flow.