Alfacalcidol LTD and LTC cause contraction in the rat
LTD4 and LTC4 cause contraction in the rat stomach and these contractions are sensitive to CysLT1 receptor antagonists (Goldenberg and Subers, 1983, Miura et al., 1992, Miyata et al., 1995). However, effects of other leukotrienes in the gastric contraction and inhibitory effects of potent, selective CysLT antagonists in the leukotriene-induced gastric contraction were not clearly known. The subtype of the cysteinyl leukotriene receptor mediating the leukotriene-induced contraction of stomach was not clear. The purpose of the present study is to characterize cysteinyl leukotriene receptors in the stomach mediating leukotriene-induced muscle contraction.
Materials and methods Male Hartley guinea pigs (300–350g) were obtained from National Laboratory Animal Center, Taiwan. LTD4, LTC4, LTE4, LTB4, montelukast and BAY u9773 were purchased from Cayman Chemical, Ann Arbor, Michigan; Carbachol, atropine, l-serine, boric acid, l-cysteine and all buffer reagents were purchased from Sigma Chemical, St. Louis, MO, USA. Tetrodotoxin was obtained from Tocris Cookson, Avonmouth Bristol, UK. l-serine borate was prepared from l-serine and boric Alfacalcidol solutions and buffered at pH 7.4 with NaOH (Bäck et al., 2001).
Discussion In the present study we demonstrated for the first time that cysteinyl leukotrienes LTC4, LTD4 and LTE4 cause moderate to marked whereas the dihydroxy leukotriene LTB4 causes only small muscle contraction in the stomach in vitro. Furthermore, we found that the leukotriene-induced contraction is mediated by CysLT1 in the fundus but by both CysLT1 and CysLT2 in the antrum. Previous studies showed LTD4 and LTC4 caused contraction of the rat stomach and these contractions were inhibited by CysLT1 receptor antagonists (Goldenberg and Subers, 1983, Miura et al., 1992, Miyata et al., 1995). In the present study we found that, in addition to LTD4 and LTC4, LTE4 caused contraction of the stomach and the relative potencies for cysteinyl leukotrienes to cause contraction were LTD4=LTC4>LTE4 in both fundus and antrum. The selective CysLT1 receptor antagonist montelukast almost abolished but only partially inhibited LTD4-induced contraction in fundus and antrum, respectively. The dual CysLT1 and CysLT2 receptor antagonist BAY u9773 partially inhibited LTD4-induced contraction in the antrum as well. We did not test the potent, selective CysLT2 antagonist HAMI3379 (Wunder et al., 2010). Interestingly, the combination of montelukast and BAY u9773 almost abolished LTD4-induced contraction in the antrum, indicating enhancement of inhibition. These indicate that leukotriene-induced contraction is mediated by CysLT1 in fundus and by both CysLT1 and CysLT2 in antrum. More studies using potent, selective CysLT2 receptor antagonists are needed to clarify the CysLT subtype mediating antral contraction. If confirmed, the leukotriene-induced contraction in the antrum mediated by both CysLT1 and CysLT2 is different to the esophagus, lower esophageal sphincter and gallbladder, in which CysLT1 mediating leukotriene-induced contraction (Falcone and Krell, 1992, Freedman et al., 1993, Chang et al., 2008, Huang, 2009), and different from ileum, in which CysLT2 mediating contraction (Bäck et al., 1996, Bäck, 2002). The effects of LTD4 were not affected by atropine or tetrodotoxin. This indicates that the cysteinyl leukotriene action is not neurally mediated and suggests a direct effect of cysteinyl leukotrienes on the gastric muscle. Direct effects have also been described on the cysteinyl leukotriene-induced contraction in the gallbladder, esophagus and lower esophageal sphincter (Freedman et al., 1993, Chang et al., 2008, Huang, 2009). In the presence of l-serine borate, the CysLT1 receptor antagonist montelukast did not inhibit and only partially inhibited the LTC4-induced contractile responses in the fundus and antrum, respectively. This is in agreement with a previous study showing a difference in the antagonist sensitivity between LTC4 and LTD4 in gastric smooth muscle cells and suggests that both CysLT1 and CysLT2 might mediate leukotriene-induced contraction not only in the antrum but also in the fundus (DeLegge et al., 1993, Bäck et al., 2001).