Interplay between nitric oxide and vasoactive intestinal polypeptide in the pig gastric fundus smooth muscle

The aim of this study was to investigate the exact mechanism of interaction between nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) as inhibitory non-adrenergic non-cholinergic (NANC) neurotransmitters in isolated smooth muscle cells and smooth muscle strips of the pig gastric fundus. In isolated smooth muscle cells, the maximal relaxant effect of VIP (10(-9) M) was inhibited by 94% by the NO synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NA, 10(-4) M) and by 85% by the inducible NOS (iNOS)-selective inhibitor N-(3-(aminomethyl)-benzyl)acetamide (1400W; 10(-6) M). The relaxant effect of VIP was reduced by more than 70% by the guanylyl cyclase inhibitor 1H-(1,2,4)oxadiazolo(4,3-a)quinoxalin-1-one (ODQ; 10(-6) M), the glucocorticoid dexamethasone (10(-5) M) and three protein kinase A inhibitors: (R)-p-cyclic adenosine-3', 5'-monophosphothioate ((R)-p-cAMPS; 10(-6) M), ¿(8R,9S, 11S)-(-)-9-hydroxy-9-n-hexylester-8-methyl-2,3,9,10-tetrahydro-8, 11-epoxy-1H,8H,11H-2,7b,11a-triazadibenzo[a, g]cycloocta[cde]-trin-den-1-one¿ (KT5720; 10(-6) M) and N-(2-(p-bromo-cinnamylamino)ethyl))-5-isoquinoline sulfonamide dihydrochloride (H-89; 10(-5) M). In contrast, no influence of the NOS inhibitors, ODQ, dexamethasone, nor the protein kinase A inhibitors could be observed on the relaxant effect of VIP in smooth muscle strips. These data demonstrate that the experimental method completely changes the influence of NOS inhibitors on the relaxant effect of VIP in the pig gastric fundus. The isolation procedure of the smooth muscle cells might induce iNOS that can be activated by VIP.