Liver and plasma concentrations in paf‐acether and its precursors after partial hepatectomy

Abstract

Liver and plasma concentrations in paf-acether (paf) and related phosphocholines, i.e., lysopaf and the ether lipid 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (AAGPC) were studied in rats following two-third hepatectomy. We report a rapid increase in hepatic content of the 3 phospholipids at early steps of the regeneration process, when hepatocytes are switching from G0 to G1 (time 2-6 h). Later on, throughout G1 and at the G1-S transition, these concentrations decreased progressively. They were back to sham-operated or intact control levels at 50 h. In the plasma of hepatectomized animals, no comparable changes were detected. However, an increase in both circulating paf and lipoprotein-bound paf concentrations was measured during the regenerating response. This report is, to our knowledge, the first one on paf level variations 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 among 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 working hypothesis. However, on the one hand, the observed paf response is 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 previously reported in vitro paf effects inducing c-fos and c-jun expression, two members of the so-called 'cellular immediate-early gene' family.