Docosahexaenoic Acid and Eicosapentaenoic Acid Inhibit the Contractile Responses of the Guinea Pig Lower Gastrointestinal Tract

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are n-3 polyunsaturated fatty acids (PUFAs), and are abundant in fish oil. These n-3 PUFAs have been reported to improve the lower gastrointestinal (LGI) disorders such as ulcerative colitis and Crohn's disease through their anti-inflammatory effects. However, there are few studies on the effect of n-3 PUFAs on motility of the LGI tract, such as the ileum and colon, the parts frequently affected by these inflammatory disorders. To elucidate the effects of DHA and EPA on the LGI tract motility, we performed comparative evaluation of their effects and linoleic acid (LA), an n-6 PUFA, on contractions in the ileal and colonic longitudinal smooth muscles (LSMs) isolated from guinea pigs. In the ileal and colonic LSMs, DHA and EPA (3 × 10^-5 M each) significantly inhibited contractions induced by acetylcholine (ACh), histamine, and prostaglandin (PG) F_2α (vs. control), and these effects are stronger than that of LA (3 × 10^-5 M). In the colonic LSMs, DHA and EPA also significantly inhibited contractions induced by PGD₂ (vs. control). In addition, DHA and EPA significantly inhibited CaCl₂-induced ileal and colonic LSM contractions in Ca²⁺-free 80 mM-KCl solution (vs. control). Any ileal and colonic LSM contractions induced by ACh, histamine, PGF_2α, and CaCl₂ were completely suppressed by verapamil (10^-5 M), a voltage-gated/dependent Ca²⁺ channel (VGCC/VDCC) inhibitor. These findings suggest that DHA and EPA could improve the abnormal contractile functions of the LGI tract associated with inflammatory diseases, partly through inhibition of VGCC/VDCC-dependent ileal and colonic LSM contractions.