Different patterns of release of endothelium‐derived relaxing factor and prostacyclin

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Abstract
1 Release of endothelium derived relaxing factor (EDRF) and prostacyclin (PGI2) from endothelial cells (EC) cultured from bovine aortae was measured by bioassay and radioimmunoassay, respectively, during infusions (10 min) of bradykinin (BK), adenosine diphosphate (ADP), arachidonic acid (AA), alkaline buffers and the free-bases (FB) of l-arginine or d-arginine. Release of EDRF from the luminally perfused rabbit aorta was also measured during infusions (10 min) of acetylcholine (ACh), substance P and ADP. 2 Bradykinin (10 or 30 nm) infused through the column of EC induced release of both EDRF and PGI2, neither of which was maintained for the duration of the infusion. 3 ADP (1.6 or 4 μm) infused through the column of EC induced release of a EDRF which was maintained for the duration of the infusion and a release of PGI2 which lasted for a much shorter period. 4 Arachdonic acid (30 or 90 μm) infused through the column of EC caused a sustained release of EDRF and PGI2, both of which outlasted the infusion of AA. 5 l-Arginine FB, d-arginine FB or alkaline buffer infused through the column of EC released EDRF, but only small amounts of PGI2. The release of EDRF outlasted the period of infusion and was due to an increase in the pH of the Krebs solution perfusing the EC. 6 Infusions of ACh (0.25–1 μm) or ADP (4–16 μm) caused a sustained release of EDRF from the luminally-perfused rabbit aorta, whereas infusion of substance P (3.3–10 μm) caused only a transient release of EDRF. 7 These results show that distinct patterns of EDRF release exist to different agonists in both cultured and in situ EC, and that EDRF and PGI2 do not necessarily follow the same time course of release. Furthermore, sustained release of EDRF does not require the constant infusion of the precursor, l-arginine, whereas sustained release of PGI2 only occurs when AA, the precursor of PGI2, is present in the extracellular medium.