Alpha-linolenic acid (ALA) inhibits contraction of pig basilar arteries through prostanoid TP receptor antagonistic action and activation of Kir channels

Introduction: Alpha-linolenic acid (ALA) is a well-known n−3 polyunsaturated fatty acid. Our previous study showed that ALA inhibits coronary contractions induced by U46619 (a thromboxane A2 analog) and prostaglandin F2α (PGF2α) in pigs by antagonizing prostanoid TP receptors. In this study, we investigated the inhibitory effects of ALA on pig basilar artery contractions and explored the underlying mechanisms. Methods: The effects of ALA on contractions of pig basilar arteries were assessed. The effects of K+ channel inhibitors on ALA-mediated attenuation were also evaluated. Results: ALA inhibited TP receptor-mediated contractions induced by U46619 and PGF2α in a concentration-dependent manner. It shifted the U46619 concentration-response curve to the right and reduced the maximal contraction. The slope of the regression line in the Schild plot analysis exceeded unity, although the difference was not statistically significant. ALA also inhibited PGF2α-induced contractions (in the presence of SQ 29,548, a TP receptor antagonist) and endothelin-1-induced contractions, without affecting those induced by high-KCl. Among the tested K+ channel inhibitors, Ba2+, an inhibitor of inwardly rectifying K+ (Kir) channels, most potently attenuated ALA's inhibitory effect on PGF2α-induced contractions in the presence of SQ 29,548. Conclusions: These findings indicate that ALA potently inhibits contractions induced by potentially spasmogenic substances in the pig cerebral artery. The inhibitory mechanisms likely involve both antagonism of prostanoid TP receptors and activation of Kir channels.