Activities of enzymes metabolizing phospholipids in rat cerebral ischemia

Ischemic rat brains were prepared by decapitation followed by incubation in an artificial cerebrospinal fluid at various times at 37 degrees C, and the levels of phospholipids, free fatty acids, and enzymes involved in their metabolism were studied. Activities of phospholipase A, phospholipase C, and di- and monoglyceride lipase, assayed with optimal concentrations of Ca2+ and lysophospholipase, did not significantly change by 60 min of ischemia, whereas acylation enzymes of lysophospholipid decreased in activity to an extent of 70% of control at 15 min after the ischemic treatment. The maximal activities were found at 8 x 10(-3)M, 1 x 10(-3) M, and 2 x 10(-2) M Ca2+ for phospholipase A, phospholipase C, and di- and monoglyceride lipases, respectively in microsomal fractions of both control and ischemic brain. Furthermore, the sensitivity of microsomal enzymes to endogenous Ca2+ was estimated in control and ischemic brain. The sensitivity of phospholipase C was found to be increased after 1 min of ischemic treatment, but those of phospholipase A and di- and monoglyceride lipase were not increased.