No abstract

The inhibitory effects of docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and linoleic acid (LA) on the contractions induced by five prostanoids and U46619 (a TP receptor agonist) were examined in guinea pig gastric fundus smooth muscle (GFSM). Tension changes were isometrically measured, and the mRNA expression of prostanoid receptors was measured by RT‐qPCR. DHA and EPA significantly inhibited contractions induced by the prostanoids and U46619, whereas LA inhibited those induced by prostaglandin D 2 and U46619. The mRNA expression levels of the prostanoid receptors were TP ≈ EP 3 >> FP > EP 1 . The inhibition by DHA, EPA, and LA was positively correlated with that by SQ 29,548 (a TP receptor antagonist) but not with that by L‐798,106 (an EP 3 receptor antagonist). DHA and EPA suppressed high KCl‐induced contractions by 35% and 25%, respectively, and the contractions induced by the prostanoids and U46619 were suppressed by verapamil, a voltage‐dependent Ca 2+ channel (VDCC) inhibitor, by 40%–85%. Although LA did not suppress high KCl‐induced contractions, it suppressed U46619‐induced contractions in the presence of verapamil. However, LA did not show significant inhibitory effects on U46619‐induced Ca 2+ increases in TP receptor‐expressing cells. In contrast, LA inhibited U46619‐induced contractions in the presence of verapamil, which was also suppressed by SKF‐96365 (a store‐operated Ca 2+ channel [SOCC] inhibitor). These findings suggest that the TP receptor and VDCC are targets of DHA and EPA to inhibit prostanoid‐induced contractions of guinea pig GFSM, and SOCCs play a significant role in LA‐induced inhibition of U46619‐induced contractions.

This study was performed to elucidate whether eicosapentaenoic acid (EPA) suppresses spasm-prone blood vessel contractions induced by a thromboxane mimetic (U46619) and prostaglandin F2α (PGF2α) and determine whether the primary target of EPA is the prostanoid TP receptor. Accordingly, we assessed: (1) the tension changes in porcine basilar and coronary arteries, and (2) changes in the Fura-2 (an intracellular Ca2+ indicator) fluorescence intensity ratio at 510 nm elicited by 340/380 nm excitation (F340/380) in 293T cells expressing the human TP receptor (TP-293T cells) and those expressing the human prostanoid FP receptor (FP-293T cells). EPA inhibited both porcine basilar and coronary artery contractions induced by U46619 and PGF2α in a concentration-dependent manner, but it did not affect the contractions induced by 80 mM KCl. EPA also inhibited the increase in F340/380 induced by U46619 and PGF2α in TP-293T cells. In contrast, EPA showed only a marginal effect on the increase in F340/380 induced by PGF2α in FP-293T cells. These findings indicate that EPA strongly suppresses the porcine basilar and coronary artery contractions mediated by TP receptor and that inhibition of TP receptors partly underlies the EPA-induced inhibitory effects on these arterial contractions.

Docosahexaenoic acid (DHA) is an n-3 polyunsaturated fatty acid abundant in fish oil. Chronic administration of DHA has been reported to improve asthma due to its anti-inflammatory effects. However, the immediate effects of DHA on isolated tracheal smooth muscle (TSM) contractility have not been studied. In this study, we investigated the potential inhibitory effects of DHA on the guinea pig TSM contractions. DHA (3 × 10 −5 M) significantly inhibited TSM contractions induced by U46619 (a thromboxane A 2 (TXA 2 ) mimetic, 10 −8 M) and prostaglandin F 2α (PGF 2α , 5 × 10 −7 M). The TSM contractions induced by U46619 (10 −8 M) and PGF 2α (5 × 10 −7 M) were significantly inhibited by SQ 29,548 (a prostanoid TP receptor antagonist, 10 −6 M). DHA (4 × 10 −5 M/6 × 10 −5 M) shifted the concentration-response curves (CRCs) for U46619 and PGF 2α to the right in a concentration-dependent manner.However, the slope of the regression line in the Schild plot of DHA vs. U46619/PGF 2α was larger than unity. In contrast, DHA (4 × 10 −5 M) did not significantly affect the CRCs for acetylcholine, histamine, and leukotriene D 4 .These findings indicate that DHA selectively inhibit prostanoid TP receptor-mediated TSM contractions. DHA may have preventive and ameliorative effects on asthma attacks associated with TSM hyper-contraction caused by TXA 2 and PGF 2α .

Eicosapentaenoic acid (EPA) is an n-3 polyunsaturated fatty acid (PUFA) found in fish oil. We recently showed that docosahexaenoic acid (DHA), another n-3 PUFA, potently inhibited pig basilar and coronary artery contractions induced by U46619 (a TP receptor agonist) and prostaglandin (PG) F 2α . We also showed that prostanoid TP receptors are potential targets for DHA. In this study, we investigated whether EPA, like DHA, suppresses contractions of pig basilar and coronary arteries induced by U46619 and PGF 2α through inhibition of the TP receptor.EPA suppressed both U46619-and PGF 2α -induced pig basilar and coronary contractions in a concentrationdependent manner without affecting 80 mM KCl-induced contractions. U46619-/PGF 2α -induced contractions in both arteries were completely/largely suppressed by SQ 29,548 (a TP receptor antagonist). In addition, EPA suppressed U46619-/PGF 2α -induced increases in intracellular Ca 2+ concentrations ([Ca 2+ ] i ) in human TP receptoroverexpressing 293T cells, whereas it showed only a slight effect on PGF 2α -induced [Ca 2+ ] i increases in human FP receptor-overexpressing 293T cells. These findings suggest that EPA strongly suppresses TP-receptor-mediated contractions of pig basilar and coronary arteries, which can be partially attributed to its inhibitory effects on the TP receptor.