Previous data from our laboratory have shown that calcitonin gene-related peptide (CGRP) has a potentiating effect on lipopolysaccharide-(LPS) induced interleukin-6 (IL-6) release from mouse macrophages. However, the mechanism of this effect was not clear. Since the nitric oxide (NO) and prostaglandins (PGs) induced by LPS might modulate IL-6 release, we examined whether NO and PGs were also involved in the potentiating effect of rat CGRP (rCGRP) on LPS-induced IL-6 release from mouse macrophages. The IL-6 level in the medium was measured by enzyme-linked immunosorbent assay. Accumulation of NO was assessed by measuring the presence of nitrite by the Greiss reaction. PGI2 was assessed by measuring the formation of 6-keto-prostaglandin F1α (6-keto-PGF1α) by radioimmunoassay. The results showed that the potentiating effect of rCGRP (0·1 nm) on LPS-induced IL-6 release was significantly inhibited by either 100 μm NG-monomethyl-l-arginine acetate (l-NMMA; an inhibitor of NO synthase) or 10 μm indomethacin (an inhibitor of cyclo-oxygenase). The LPS-induced NO and PGI2 production from these cells was increased significantly by rCGRP at 0·01–10 nm in a concentration-dependent manner, which was blocked by l-NMMA and indomethacin. These results suggest that rCGRP enhances the NO production elicited by LPS and subsequently increases the PGs production which is involved in the potentiating effect of rCGRP on LPS-induced IL-6 release from the peritoneal macrophages in the mouse
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