Effects of Ergot Alkaloid Exposure on Serotonin Receptor mRNA in the Smooth Muscle of the Bovine Gastrointestinal Tract

Abstract Text:

Various serotonin (5HT) receptor subtypes have been located in the gastrointestinal tract and some are associated with gut motility. Cattle exposed to ergot alkaloids through consumption of contaminated feedstuffs have demonstrated signs (e.g. - increased rumen DM content and total content) that suggest a reduction in gut motility. Ergot alkaloids have been shown to interact with biogenic amine receptors and specifically serotonin receptors. Therefore, the objective of this study was to evaluate the effect of dietary exposure to ergot alkaloids has on the expression of 5HT receptor subtypes 5HTR2A (NM_001001157.1) and 5HTR4 (NM_001010485.1) in the smooth muscle of the reticulum, rumen, omasum, abomasum, duodenum, jejunum, ileum, cecum and colon of cattle. Ruminally cannulated Angus steers (n=12; BW=547±31 kg) were paired by weight and randomly assigned to 6 blocks. Steers were fed alfalfa cubes at 1.5 × NE_m and were ruminally dosed daily with 1 kg of either endophyte-infected (E+; 4.45 ppm ergovaline) or endophyte-free (E-) tall fescue seed for 21 d prior to slaughter. On d 22 steers were slaughtered and samples of smooth muscle from the different sites of the gastrointestinal tract were sampled, rinsed, homogenized in Tri-reagent, and total RNA was isolated. Semi-quantitative real-time PCR was conducted using SYBR green and glyceraldehyde 3-phosphate dehydrogenase (NM_001034034.2) as a reference gene. Resultant data were analyzed using mixed models of SAS. There was no interaction of sampling location by seed treatment for either gene evaluated. For 5HTR4 only the main effect of sampling location was significant (P < 0.001) with ileum and jejunum having the greatest amount of transcript (P < 0.05) followed by the colon and duodenum (P < 0.05). The remaining tissue sites did not differ. Expression of 5HTR2A in E- steers was greater (P = 0.04) than E+ steers with lower relative quantities of 5HTR2A in E+ steers for all tissue sampling locations except the abomasum (P = 0.054). The enteric 5HTR2A receptor is associated with smooth muscle contraction and the observed decrease in expression in E+ treated steers suggests that ergot alkaloids may play a role in negatively affecting gut motility. Future work will explore the effects alkaloids might have on genes that encode for the G proteins and other downstream signal transduction proteins associated with these 5HT receptors.

Keywords: Bovine, ergot alkaloids, serotonin receptor