EFFECTS OF ANOXIC STRESS ON PROSTAGLANDIN-H SYNTHASE ISOFORMS IN PIGLET BRAIN

We examined effects of ischemia and asphyxia on levels of prostaglandi n H synthase-l (PGHS-1) and prostaglandin H synthase-2 (PGHS-2) in pig let brain. Ischemia was induced by increasing intracranial pressure an d asphyxia was induced by turning off the respirator. Duration of anox ic stress was 10 min. In some animals, indomethacin (5 mg/kg, i.v.) or 7-nitroindazole (7-NI) was administered prior to ischemia to block PG HS or brain nitric oxide synthase (bNOS), respectively. Tissues from c erebral cortex and hippocampus were removed and fixed and/or frozen af ter 1, 2, 4 and 8 h of recovery from anoxic stress. In addition, tissu es were obtained from untreated animals or from time control animals. Levels of mRNA and proteins were determined using RNase protection ass ay and immunohistochemical approaches, respectively. In the tissues st udied, only a few neurons were immunopositive for PGHS-1, and neither ischemia or asphyxia affected PGHS-1 immunostaining at 8 h after recov ery. Likewise, PGHS-1 mRNA did not increase following anoxic stress. I n contrast, substantial PGHS-2 immunoreactivity was present in neurons and glial cells in the cerebral cortex and hippocampus and there was no difference between time control and non treated animals. PGHS-2 mRN A increased by 2-4 h after ischemia, and heightened immunoreactivity f or PGHS-2 was present at 8 h after ischemia in cerebral cortex and hip pocampus. However, asphyxia did not increase PGHS-2 mRNA or immunostai ning. Indomethacin pretreatment inhibited increases in mRNA and protei n for PGHS-2 after ischemia, while 7-NI had little effect on increases in PGHS-2 immunoreactivity. We conclude that: (1) PGHS-2 is the predo minant isoform present in piglet cerebral cortex and hippocampus; (2) Ischemia but not asphyxia increases levels of PGHS-2; (3) Ischemia doe s-not increase levels of PGHS-1; and (4) Indomethacin but not 7-NI att enuates ischemia-induced increases in PGHS-2. (C) 1998 Elsevier Scienc e B.V.