Inhibitory effect of pentobarbital on phospholipase C activity in ischaemic rat brain

Ischaemic rat brains were examined for temporal changes in phospholipase C activity with phosphatidylinositol; the effects of pentobarbital on the activity also were investigated. Ischaemia was produced by decapitation. Pentobarbital (60 mg/kg) was administered i.p. for 15 min before decapitation. The removed heads were incubated at 37 degrees C for 1, 5, 15 or 30 min and then quickly frozen in liquid nitrogen. After isolation of subcellular fractions from the brains, phospholipase C activity was measured for cytosol and microsomes, using radioactive phosphatidylinositol as a substrate. The results demonstrated that brain phospholipase C predominantly localized in the cytosol was dependent on Ca2+ for full activity and had neutral pH optima. Although the enzyme activity did not increase during ischaemia, pentobarbital inhibited phospholipase C activity in the cytosol but not in the microsomes. These observations suggest that pentobarbital may exert a cerebral protective action due to, at least in part, the repression of phospholipase C followed by a reduction of phosphatidylinositol breakdown, preventing perturbation to the integrity of membranes, during ischaemia.