LIVER AND PLASMA-CONCENTRATIONS IN PAF-ACETHER AND ITS PRECURSORS AFTER PARTIAL-HEPATECTOMY

Liver and plasma concentrations in paf-acether (paf) and related phosp hocholines, i.e. lysopaf and the ether lipid 1-O-alkyl-2-acyl-sn-glyce ro-3-phosphocholine (AAGPC) were studied in rats following two-third h epatectomy. We report a rapid increase in hepatic content of the 3 pho spholipids at early steps of the regeneration process, when hepatocyte s are switching from G(0) to G(1) (time 2-6 h). Later on, throughout G (1) and at the G(1)-S transition, these concentrations decreased progr essively. They were back to sham-operated or intact control levels at 50 h. In the plasma of hepatectomized animals, no comparable changes w ere detected. However, an increase in both circulating paf and lipopro tein-bound paf concentrations was measured during the regenerating res ponse. This report is, to our knowledge, the first one on paf level va riations following 2/3 hepatectomy. In rats, partial resection of the liver was shown to initiate rapid and complex cascades of biochemical changes involving growth factors, neurotransmitters and interleukins a mong others. Our data are in good agreement with reported increases in both total phospholipid content and synthesis of phosphatidylcholine, a paf precursor, in the regenerating liver. At present, the possible functional significance of high paf concentrations measured over the ' priming' stage of the induced proliferative wave is suggested as a wor king hypothesis. However, on the one hand, the observed paf response i s noteworthy in view of its cytokine-related action, i.e. stimulation of IL-6 production by different cell types (endothelial, macrophagic). On the other hand, it could represent an in vivo confirmation of prev iously reported in vitro paf effects inducing c-fos and c-jun expressi on, two members of the so-called 'cellular immediate-early gene' famil y.