DISAPPEARANCE OF 2 MAJOR PHOSPHATIDYLCHOLINES FROM PLASMA IS PREDOMINANTLY VIA LCAT AND HEPATIC LIPASE

Metabolism of 1-stearoyl-2-arachidonyl-phosphatidylcholine (SAPC), a m ajor phosphatidylcholine (PC) species in rat plasma, was compared with 1-palmitoyl-2-linoleoyl-PC (PLPC) metabolism. High-density lipoprotei ns containing SAPC and PLPC tracers labeled in the sn-2 fatty acid wit h H-3 and C-14 isotopes, respectively, were administered. The rats wer e depleted of endogenous bile acids and infused via the ileum with ind ividual bile acids that ranged widely in hydrophobicity. The half-live s for SAPC and PLPC in plasma were 48 and 57 min, respectively. Most o f the H-3 activity that disappeared from plasma at 1 h was found in th e liver in 1-palmitoyl-2-arachidonyl-PC, SAPC, and 1-oleoyl-2-arachido nyl-PC, indicating phospholipase A(1) hydrolysis of plasma SAPC formin g 2-arachidonyl-lysophosphatidylcholine, which was reacylated in the l iver. Plasma PLPC also underwent phospholipase A(1) hydrolysis, as rep orted previously. The fraction of H-3 dose that accumulated in plasma cholesteryl arachidonate was two- to threefold higher than the fractio n of C-14 dose in cholesteryl linoleate. Multicompartmental models for SAPC and PLPC were developed that included lysophosphatidylcholines a nd cholesteryl esters. Bile acids did not influence plasma PC metaboli sm. Lecithin-cholesterol acyltransferase and phospholipase A(1) (hepat ic lipase) hydrolysis accounted for greater than or equal to 90% of th e SAPC and PLPC that disappeared from plasma; SAPC and PLPC are compar able as substrates for hepatic lipase, but SAPC is preferred by lecith in-cholesterol acyltransferase.