5-Hydroxytryptamine-4 receptor messenger ribonucleic acid levels and densities in gastrointestinal muscle layers from healthy dairy cows1

Pharmacologic assessment of bovine ruminal and mesenteric vascular serotonin receptor populations

Prior work using a contractility bioassay determined that the serotonin (5-HT) receptor subtype 5-HT2A is present in bovine lateral saphenous veins and plays a role in ergot alkaloid (EA)-induced vascular contraction in steers grazing endophyte-infected (Epichloë coenophiala) tall fescue (Lolium arundinaceum). Ergot alkaloids have also been shown to be vasoactive in bovine gut vasculature. To determine what 5-HT receptors are involved in vasoconstriction of gut vasculature, contractility of ruminal and mesenteric arteries and veins collected from cattle was evaluated in the presence of agonists selective for 5-HT1B (CP 93129), 5-HT1D (L-694, 247), 5-HT2A (TCB-2), 5-HT2B (BW 723C86), 5-HT4 (BIMU-8), and 5-HT7 (LP 44) receptors. Segments of ruminal and mesenteric veins and arteries were collected and suspended in a multimyograph containing continuously oxygenated Krebs-Henseleit buffer. Blood vessels were exposed to increasing concentrations of 5-HT agonists every 15 min and contractile response data were normalized as a percentage of the maximum contractile response induced by 120 mM KCl. Analysis of variance was evaluated using mixed models procedure of SAS for effects of agonist concentration for each vessel type. Receptor agonists for 5-HT2B, 5-HT1D, and 5-HT7 did not induce a contractile response for ruminal or mesenteric vasculature (P > 0.05). However, when exposed to agonists for 5-HT2B or 5-HT1D, mesenteric veins relaxed below zero (P < 0.05). Exposure of all 4 blood vessel types to 5-HT2A agonist induced contractile responses (P < 0.05). The findings of this study indicate that 5-HT1D and 5-HT2B are present in mesenteric veins and may play a role in vasorelaxation. Further, 5-HT2A is present in ruminal and mesenteric vasculature, plays a role in vasoconstriction of these vessels, and could be influenced by EA exposure as has been demonstrated in peripheral blood vessels.

Role of the serotoninergic system in the development of diseases of the intestinal and biliferous tracts

Primary sclerosing cholangitis and nonspecific ulcerative colitis were modeled before and after serotonin and spiperone injections. Activation of the serotoninergic system prevented the development of primary sclerosing cholangitis, but promoted more severe course of nonspecific ulcerative colitis.

Messenger RNA Levels and Binding Sites of Muscarinic Acetylcholine Receptors in Gastrointestinal Muscle Layers from Healthy Dairy Cows

Acetylcholine interacts with muscarinic receptors (M) to mediate gastrointestinal (GI) smooth muscle contractions. We have compared mRNA levels and binding sites of M(1)to M(5) in muscle tissues from fundus abomasi, pylorus, ileum, cecum, proximal loop of the ascending colon (PLAC), and external loop of the spiral colon (ELSC) of healthy dairy cows. The mRNA levels were measured by quantitative RT-PCR. The inhibition of [(3)H]-QNB (1-quinuclidinyl-[phenyl-4-(3)H]-benzilate) binding by M antagonists [atropine (M(1 - 5)), pirenzepine (M(1)), methoctramine (M(2)), 4-DAMP (M(3)), and tropicamide (M(4))] was used to identify receptors at the functional level. Maximal binding (B(max)) was determined through saturation binding with atropine as a competitor. The mRNA levels of M(1), M(2), M(3), and M(5) represented 0.2, 48, 50, and 1.8%, respectively, of the total M population, whereas mRNA of M(4) was undetectable. The mRNA levels of M(2) and of M(3) in the ileum were lower (P < 0.05) than in other GI locations, which were similar among each other. Atropine, pirenzepine, methoctramine, and 4-DAMP inhibited [(3)H]-QNB binding according to an either low- or high-affinity receptor pattern, whereas tropicamide had no effect on [(3)H]-QNB binding. The [(3)H]-QNB binding was dose-dependent and saturable. B(max) in fundus, pylorus, and PLAC was lower (P < 0.05) than in the ELSC, and in the pylorus lower (P < 0.05) than in the ileum. B(max) and mRNA levels were negatively correlated (r = -0.3; P < 0.05). In conclusion, densities of M are different among GI locations, suggesting variable importance of M for digestive functions along the GI tract.