文摘
ABSTRACT. Calcitonin gene-related peptide (CGRP) plays a significant role in the non-adrenergic non-cholinergic (NANC) regulation of intestinal tract motility. In this work, the contractile properties of enzymatically isolated circular smooth muscle cells (SMC) from human colon in response to CGRP were evaluated. Relaxation by CGRP (1 μM) was determined in cells maximally contracted by carbachol (CCh, 1 nM). Simultaneously, cGMP contents of SMC were measured by radioimmunoassay. CCh-induced contraction was inhibited by 1 μM CGRP (maximum: 69 ± 5 % within 60 sec); similarly, exposure of cells to sodium nitroprussiate (SNP),1 μM, fully inhibited contraction (maximum: 89 ± 8 % within 30 sec). In the same time-course as for relaxation, CGRP and sodium nitroprussiate caused significant increase in intracellular cGMP levels (2- and 10-fold that of the basal level, respectively, P < 0.01). The nitric oxide synthase (NOS) inhibitor, l-N5(I-iminoethyl)ornithine, dihydrochloride, (l-NIO), 1 μM, partly inhibited SMC relaxation induced by CGRP (78.26 % ); the protein kinase inhibitor, N-(2-aminoethyl)-5-isoquinolinesulfonamide hydrochloride (H9), 1 μM, and the selective cAMP-dependent protein kinase inhibitor, adenosine-3′,5′-monophosphorothioate triethylammonium salt, Rp isomer, (Rp-cAMP(S)), 1 μM, also caused inhibition of relaxation (70.30 % and 28.6 % , respectively). In parallel, the increase in cGMP caused by CGRP was partly reduced by l-NIO (65.47 % ) and by H9 (55 % ). In conclusion, the nitric oxide generation following exposure of human colonic SMC to sodium nitroprussiate causes relaxation through the cGMP pathway; on the other hand, exposure of SMC to CGRP causes relaxation in part by activation of nitric oxide synthase and guanylate cyclase and in part through the cAMP pathway.
