Abstract

In many isolated tissues, including glomerular mesangial cells and endothelial cells, the synthesis of platelet activating factor (PAF) occurs by remodeling the phospholipids so that the production of PAF results in the release of arachidonic acid with subsequent production of cyclooxygenase or lipoxygenase products. In some tissues, including the renal medulla, another pathway for PAF biosynthesis (the de novo pathway) has been found in which the production of PAF is not linked to the production of arachidonic acid products. We tested the hypothesis that the remodeling pathway was active in the release of PAF into renal venous effluent of the isolated kidney. Isolated rat kidneys perfused at constant flow with albumin-containing buffer were stimulated to produce prostaglandin by an infusion of angiotensin II or bradykinin. Some kidneys were also challenged with the calcium ionophore A23187. Perfusate was collected for bioassay of PAF and radioimmunoassay of prostaglandin (PG) E2; urine was collected for PAF bioassay. Angiotensin II (10(-9) to 10(-8) M) increased renal vascular resistance, and bradykinin (10(-8) to 10(-7) M) and A23187 (3 x 10(-6) M) reduced renal vascular resistance. PGE2 production was increased significantly by bradykinin and angiotensin II but not by A23187. Only A23187 increased the release of PAF into the perfusate. Urine PAF was not changed by any of the stimuli. These data indicate that the release of PGE2 by the isolated, perfused rat kidney can be dissociated from the release of PAF. The findings support the suggestion that PAF released by the kidney into the renal venous effluent is not produced by remodeling the lipids that are the source of renally released prostaglandins.