Effects of phenylephrine and dopamine on cerebral blood flow, blood volume, and oxygenation in young rabbits

The effects of phenylephrine and dopamine on cerebral blood flow, blood volume, and oxygenation were studied in young rabbits using a hydrogen gas clearance method and near-infrared spectrometry. Phenylephrine infusion led to an increase in blood pressure and cerebral blood flow without changes in cerebral blood volume and oxygenation. This result suggests that phenylephrine increases arterial blood flow and vascular resistance in vascular beds which may lead to the rupture of weak vessels in premature infants. Cytochrome a, a3, however, was not affected by the drug. Conversely, a low-dose dopamine infusion had no effect on cerebral hemodynamics, but high-dose decreased blood pressure and cerebral oxyhemoglobin, and increased deoxyhemoglobin without appreciable changes in cerebral blood flow, which suggests venous congestion and arterial blood reduction in the brain.