ABSTRACT.Cerebral hyperperfusion associated with hypertension, may play an important role in the pathogenesis of intraventricular hemorrhage in preterm infants. To examine the effect of hypertension on changes in total and regional brain blood flow (BBF), we increased the mean arterial blood pressure (MABP) in nine awake newborn piglets by an infusion of 0.7 mg/kg of metaraminol bitar-trate (Aramine) (group I) and studied cerebral circulatory changes. In order to prevent the Aramine-associated bradycardia, we pretreated nine other piglets with atropine, which produced a higher level of hypertension (group II). MABP and BBF were measured and cerebral vascular resistance (CVR) was calculated during baseline, the Aramine infusion, and twice at decreasing MABP following the discontinuation of the Aramine infusion. In group I, the significant increase in MABP from 68 ± 3 to 100 ± 3 mm Hg (mean ± SEM) during the Aramine infusion resulted in a significant increase in BBF (98 ± 9 to 118 ± 11 ml-min−1100 g−1)- MABP decreased significantly (although remained significantly above baseline levels), when Aramine was discontinued; however, total BBF remained elevated. CVR increased during the Aramine infusion, but decreased significan(versusthe Aramine-infused state) in the post-Aramine period. Regional BBF increased significantly to the cerebrum and cerebellar cortex, but remained unchanged to the other regions including the brain stem. In group II, the Aramine infusion resulted in a significantly greater increase in MABP, a sustained increase in vascular resistance, and no increase in total BBF. Thus, atropine prevents increased BBF during hypertension in the newborn piglet.