Mechanisms of L-N-G nitroarginine/indomethacin-resistant relaxation in bovine and porcine coronary arteries

1 Coronary arteries from bovines (BCA) and pigs (PCA) were used for measuring endothelium-dependent relaxation in the presence of L-N-G nitroarginine and indomethacin. As some compounds tested have been found to have an inhibitory effect on autacoid-activated endothelial Ca2+ signalling, endothelium-dependent relaxation was initiated with the Ca2+ ionophore A23187. 2 The common compounds for modulating arachidonic acid release/pathway, mepacrine and econazole only inhibited L-N-G nitroarginine-resistant relaxation in BCA not in PCA. In contrast, proadifen (SKF 525A) diminished relaxation in BCA and PCA. Mepacrine and proadifen inhibited Hoe-234-initiated relaxation in BCA and PCA, while econazole only inhibited Hoe 234-induced relaxation in PCA. Due to the multiple effects of these compounds, caution is necessary in the interpretation of results obtained with these compounds. 3 The inhibitor of Ca2+-activated K+ channels, apamin, strongly attenuated A23187-induced L-N-G nitroarginine-resistant relaxation in BCA while apamin did not affect L-N-G nitroarginine-resistant relaxation in PCA. 4 Pertussis toxin blunted L-N-G nitroarginine-resistant relaxation in BCA, while relaxation of PCA was not affected by pertussis toxin. 5 Thiopentone sodium inhibited endothelial cytochrome P450 epoxygenase (EPO) in PCA but not in BCA, while L-N-G nitroarginine-resistant relaxation of BCA and PCA were unchanged. Protoporphyrine IX inhibited EPO in BCA and PCA and abolished L-N-G nitroarginine-resistant relaxation of BCA not PCA. 6 An EPO-derived compound, 11,12-epoxy-eicosatrienoic acid (11,12-EET) yielded significant relaxation in BCA and PCA in three out of six experiments. 7 These findings suggest that L-N-G nitroarginine-resistant relaxation in BCA and PCA constitutes two distinct pathways. In BCA, activation of Ca2+-activated K+ channels via a pertussis-toxin-sensitive G protein and EPO-derived compounds might be involved. In PCA, no selective inhibition of L-N-G nitroarginine-resistant relaxation was found.