Activities of enzymes metabolizing phospholipids in rat cerebral ischemia

Abstract

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.

Changes in lipid metabolites and enzymes in rat brain due to ischemia and recirculation

“…No significant changes in the levels of individual phospholipids, except polyphosphoinositides, could be detected during ischemia (Table 1). In our previous report, the changes of FFA and phospholipid were measured in decapitated brain (Hirashima et al 1989). These lipid changes agreed closely with the changes obtained from this 4-vessel occlusion model.…”

“…In a previous article, we reported that inactivation of acylation enzymes of lysophospholipid during ischemia and indicated that both ATP exhaustion and inactivation of these enzymes may be involved in the accumulation of FFA and lysophospholipids during ischemia (Hirashima et al, 1989). In the present study, we could not find a statistically significant increase in lysophospholipids during ischemia.…”

“…Phospholipase A l coupled with LPL, or plasmalogenase coupled with LPL, may also be involved in the liberation of FFA from phospholipids (Van den Bosch, 1982;Horrocks Changes in Lipid Metabolites and Enzymes 37 et al, 1984). Additionally, in a previous study, we have described that inactivation of reacylation enzymes of lysophospholipid contribute to the accumulation of FFA during ischemia (Hirashima et al, 1989). However, the relative contribution of these pathways during ischemia remains uncertain.…”

“…Subcellular fractions were prepared by the method of Shum et al (1979), and protein was determined by the method of Lowry et al (1951). The procedures for enzyme assays were described in detail in our previous communication (Hirashima et al, 1989). These procedures included the following: (1) incubation of exogenous radioisotope-labeled substrate with aliquot of the subcellular fraction (2) separation of product and substrate in the reaction mixture by TLC or another method, and (3) the measurement of radioactivity of reaction and [1-14C]arachidonic acid were used as radioactive substrates.…”

“…PLA, PLC, and DG+MG lipase are Ca t -dependent (Hirashima et al, 1989). These enzyme activities were measured at optimal Ca t concentration.…”