Distribution of mRNA that codes for 5-hydroxytryptamine receptor subtypes in the gastrointestinal tract of dairy cows

<jats:title>Abstract</jats:title> <jats:p> <jats:bold>Objective</jats:bold>—To describe the distribution of mRNA that codes for 8 subtypes of 5-hydroxytryptamine receptors (5-HTRs) in the digestive tract of dairy cows.</jats:p> <jats:p> <jats:bold>Sample Population</jats:bold>—Fresh full-thickness wall specimens from the abomasum (fundus, corpus, and antrum), ileum, cecum, proximal loop of ascending colon, and 4 locations of the spiral colon collected from 10 healthy cows at slaughter.</jats:p> <jats:p> <jats:bold>Procedure</jats:bold>—Concentrations of mRNA that code for 5-HTR subtypes (5-HTR<jats:sub>1A</jats:sub>, 5-HTR<jats:sub>1B</jats:sub>, 5-HTR<jats:sub>1D</jats:sub>, 5-HTR<jats:sub>1F</jats:sub>, 5-HTR<jats:sub>2A</jats:sub>, 5-HTR<jats:sub>2B</jats:sub>, 5-HTR<jats:sub>2C</jats:sub>, and 5-HTR<jats:sub>4</jats:sub>) in the bovine digestive tract were measured by use of a quantitative real-time reverse transcription-polymerase chain reaction assay. Results were reported in relation to mRNA expression of the housekeeping gene glyceraldehyde phosphate dehydrogenase (GAPDH).</jats:p> <jats:p> <jats:bold>Results</jats:bold>—Mean relative mRNA concentrations for 5-HTR were low (range, 0% to 1.32% of GAPDH), and mRNA that codes for 5-HTR<jats:sub>1A</jats:sub> was not detected. In the abomasum, mRNA expression was highest for 5-HTR<jats:sub>1B</jats:sub> and 5-HTR<jats:sub>2B</jats:sub>, followed by subtypes 1F, 2A, 1D, and 4, whereas 5-HTR<jats:sub>2C</jats:sub> was not detected. In intestinal samples, concentrations of subtypes 1B, 2B, and 4 were highest, followed by 1D, 1F, 2A, and 2C. Relative concentrations of mRNA that code for 5-HTR<jats:sub>2A</jats:sub> were significantly higher in the abomasum than the intestines, but lower for 5-HTR<jats:sub>2B</jats:sub>, 5-HTR<jats:sub>2C</jats:sub>, and 5-HT<jats:sub>R4</jats:sub>.</jats:p> <jats:p> <jats:bold>Conclusions and Clinical Relevance</jats:bold>—Relative concentrations of mRNA that code for 5-HTRs differ among locations in the gastrointestinal tract of cattle. Understanding differences in the distribution of 5- HTRs in healthy cattle and cattle with gastrointestinal tract disease may lead to improved therapeutic approaches for abomasal and cecal motility disorders. (<jats:italic>Am J Vet Res</jats:italic> 2004;65:1151–1158)</jats:p>