The prostaglandin H-synthase inhibitor indomethacin decreases cerebral blood flow (CBF) in newborn pigs. The duration of this effect on CBF has not been established in piglets in the awake state. The purpose of the study was to determine in awake piglets the duration of cerebral vascular responses to a single dose of indomethacin and the CBF responses to a second dose of indomethacin. Two groups of animals were studied. Newborn pigs 3-5 d old were instrumented the day before experiments. On the next day, sagittal sinus catheters were placed after the piglets were given local anesthesia. The experiments were performed on unanesthetized piglets that were put in a cloth sling and fed via an orogastric tube. In the first group of piglets (n = 8), the baseline CBF (microspheres) and cerebral metabolic rate for oxygen (CMRO2) measurements were made 30 min after sagittal sinus catheter placement. Indomethacin (5 mg/kg i.v.) was then given slowly over a 5-min period, and CBF and CMRO2 measurements were made at 10, 60, 120, and 240 min. Total CBF (mean +/- SEM) decreased significantly after indomethacin administration from 98 +/- 12 mL.min-1.100 g-1 to 50 +/- 3, 56 +/- 7, and 70 +/- 11 mL.min-1.100 g-1 at 10, 60, and 120 min, respectively. The total CBF returned to baseline levels at 240 min (101 +/- 16 mL-1.min-1.100 g-1).(ABSTRACT TRUNCATED AT 250 WORDS)