Generation of arachidonic acid and diacylglycerol second messengers from polyphosphoinositides in ischemic fetal brain.
Intracerebral administration of [3H]arachidonic acid ([3H]ArA) into 19-20-day-old rat embryos, resulted in a rapid incorporation of label into brain lipids. One hour after injection, 55.6 +/- 8.2, 18.0 +/- 3.4, and 13.7 +/- 1.3% of the total radioactivity was associated with phosphatidylcholine, phosphatidylinositol, and phosphatidylethanolamine, respectively. Approximately 10% of radioactivity was found acylated in neutral lipids of which free ArA comprised only 1.5 +/- 0.2% of the total radioactivity. Complete restriction of the maternal-fetal circulation for < or = 40 min did not affect the rate of [3H]ArA incorporation (t1/2 = 2 min) into fetal brain lipids, suggesting an effective acylation mechanism that proceeds irrespective of the impaired blood flow. After a short restriction period (5 min), the radioactivity in diacylglycerol was elevated by 50%. After a longer restriction period (20 min), the radioactivity in the free fatty acid and diacylglycerol fractions increased to values of 130 and 87%, respectively. Polyphosphoinositides prelabeled with either [3H]ArA or 32P were rapidly degraded after 5 min of ischemia. After 20 min, the decrease in phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate radioactivity was 47 and 70%, respectively. Double labeling of phospholipids with [14C]palmitic acid and [3H]ArA indicated a preferential loss of [3H]ArA within the polyphosphoinositide species after 20 min, but not after 5 min of ischemia. The specific activity of [14C]palmitate remained unchanged. The current data suggest phospholipase C-mediated diacylglycerol formation at the beginning of the insult followed by a phospholipase A2-mediated ArA liberation at a later time, both enzymes presumably acting preferentially on polyphosphoinositide species.
Kunievsky
B
B
Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
Bazan
N G
NG
Yavin
E
E
D000818:Animals; D001095:Arachidonic Acids / Q000008:administration & dosage / Q000378:metabolism*; D001921:Brain; D002545:Brain Ischemia / Q000196:embryology / Q000201:enzymology / Q000378:metabolism*; D004075:Diglycerides / Q000378:metabolism*; D004789:Enzyme Activation / Q000502:physiology; D005260:Female; D005333:Fetus; D007276:Injections, Intraventricular; D010713:Phosphatidylcholines / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000145:classification / Q000378:metabolism*; D011247:Pregnancy; D011493:Protein Kinase C / Q000378:metabolism / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D015290:Second Messenger Systems / Q000502:physiology*
D001095:Arachidonic Acids; D004075:Diglycerides; D010713:Phosphatidylcholines; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D011493:Protein Kinase C