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Urine from normotensive volunteers and patients with systemic lupus erythematosus glomerulonephropathy was sequentially concentrated by negative-pressure ultrafiltration, dialyzed against distilled water, and extracted into the chloroform phase of a mixture of organic solvents(chloroform:methanol:water, 1:1:0.9 vol/vol). The lipid fraction was further purified by thin-layer chromatography on silica gel plates using neutral, acidic, and basic mixtures of organic solvents and it was then tested for its ability to induce the release of [3H]serotonin from rabbit platelets. All of the samples contained a platelet-activating moiety similar to a synthetic platelet-activating factor (PAF-acether) on the basis of its chromatographic behavior, resistance to the pretreatment of platelets by 10(-6) M indomethacin, and loss of activity by alkaline methanolysis or treatment by phospholipases A2, C, and D. Cross-densensitization experiments between synthetic PAF-acether and the urine factor showed that both compounds act on platelets through the activation of the same putative receptor. Further, the urine factor induced hypotension when intra-arterially injected in normotensive rats, and this activity was also abrogated by alkaline methanolysis. In summary, these data provide evidence of the presence in normal human urine and, probably, of the release by the kidney of a lipid factor with platelet-activating and hypotensive activity whose general structure seems to be alkyl-acyl-glyceryl-phosphorylcholine and, therefore, is similar to the structure of the inflammatory mediator PAF-acether and the antihypertensive polar renomedullary lipid.

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