12-HYDROXYEICOSATETRAENOIC ACID IS A LONG-LIVED SUBSTANCE IN THE RABBIT CIRCULATION

12-Hydroxyeicosatetraenoic acid (12-HETE) is one of the major metaboli tes formed from arachidonic acid in platelets. We have recently shown that the in vitro metabolism of 12-HETE by human leukocytes, with and without stimulation, is effectively inhibited by the addition of physi ological concentrations of albumin, probably by sequestration of the c ompound. In the present paper, we have studied the in vivo metabolism of 12-HETE in the rabbit, using either [1-C-14]- or [C-14(U)12-HETE. D istribution of radioactivity was followed in urine, plasma, and bile, as well as in a number of tissues. In most of the tissues examined, th e hydrophilic radioactivity constituted more than 50% of the total rad ioactivity after 20 min. When the lipophilic fraction was analyzed, ar ound 15% of the radioactivity was shown to be unesterified 12-METE, an d only a very minor part could be detected as metabolites. The dominat ing lipophilic compound in the circulation after i.v. administration o f radiolabeled 12-HETE was at all time points (1-60 min.) the parent c ompound, as analyzed by HPTLC and HPLC. A comparison of the plasma met abolite profiles obtained when [1-C-14]- and [C-14(U)]12-HETE were use d displayed almost identical patterns, thus indicating that beta-oxidi zed metabolites either were not formed or were rapidly removed from th e circulation. The appearance of large amounts of water-soluble radioa ctivity with time supported the latter conclusion. Several minor metab olites were seen that chromatographed in the dihydroxy acid region as judged by HPLC and TLC. The major one of these compounds represented a bout 10% of the lipophilic plasma radioactivity after 60 min., while u nmetabolized 12-HETE at this stage still represented about 30%. The me tabolite had a polarity similar to 12,20-dihydroxyeicosatetraenoic aci d; however, when chromatographed together, these two compounds separat ed, indicating a different structure of the metabolite. Our findings a re in agreement with in vitro data concerning the protective effect of albumin on the metabolism of 12-HETE and is the first extensive metab olic study of 12-HETE in vivo covering all metabolic possibilities inv olving the carbon skeleton.