Modification of spontaneous contractility of smooth muscle preparations from the bovine abomasal antrum by serotonin receptor agonists

Abstract

The effects of serotonin (5-hydroxytryptamine, 5-HT), a 5-HT2-receptor agonist, alpha-methyl-5-hydroxytryptamine (alpha-M-5-HT) and RS-67506, a 5-HT4 receptor partial agonist, on spontaneous contractility of bovine abomasal smooth muscle preparations were investigated in vitro. Preparations from the abomasal antrum of freshly slaughtered healthy dairy cows were cut parallel to the longitudinal fibres, suspended in isolated organ baths, and concentration-response curves were performed by cumulative application of the 5-HT receptor agonists. Blockade of 5-HT2-induced response was tested with atropine and hexamethonium. Serotonin evoked a significant increase in the area under curve (AUC), whilst the 5-HT2 receptor agonist alpha-M-5-HT significantly increased the AUC and resting tone (RT). RS-67506 induced a significant increase in AUC and RT and a significant decrease in the maximum force. The effect of alpha-M-5-HT was mediated by a muscarinic cholinergic pathway, as the effect of alpha-M-5-HT was inhibited in the presence of atropine but not hexamethonium. It is concluded that 5-HT2 and 5-HT4 receptors are present in the bovine abomasal antrum. Muscarinic receptors are involved in the increase in RT seen after 5-HT2 receptor stimulation.

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

“…69 However, the addition of a partial 5-HTR 4 agonist to the organ bath solution led to an increase in resting tone of longitudinal muscle strips from the abomasal antrum. 66 In the study reported here, we found high relative amounts of mRNA that code for 5-HTR 4 in all intestinal samples, which were approximately 100 times higher than the amounts measured in the abomasum. These results are in contrast to the lack of effects of cisapride in the intestine of cattle.…”

“…A specific 5-HTR 2 agonist (α α-methyl-5-hydroxytryptamine [α α-M-5-HT]) can increase in vitro contractility of specimens from the abomasal antrum through a mechanism involving muscarinic cholinergic pathways. 66 Motor responses of intestinal samples to α-M-5-HT have not been investigated, and this agonist does not allow for identification of the 5-HTR 2 subtype or subtypes involved in the mediation of effects. However, an increase of abomasal contractility in response to a 5-HTR 2 agonist could be compatible with the relatively high mRNA expression for 5-HTR 2B throughout the gastrointestinal tract of cattle and with the high relative concentration of 5-HTR 2A mRNA in the abomasum, compared with the intestine, observed in our study.…”

Invited review: Abomasal emptying in calves and its potential influence on gastrointestinal disease

“…Nitric oxide is a major local mediator that affects abomasal motility and emptying (Adams, 1996;Sun et al, 1998). Serotonin affects the motility of the entire gastrointestinal tract because it activates both intrinsic and extrinsic primary afferent neurons to initiate peristaltic and secretory reflexes and to transmit this information to the central nervous system (Spring et al, 2003;Meylan et al, 2004b). Insulin also affects abomasal emptying (van Meirhaeghe et al, 1988), and hyperglycemic animals with increased endogenous insulin secretion or animals that have been given exogenous insulin injections show decreased abomasal emptying rates of up to 50% for a few hours.…”

Expression of Messenger RNA Coding for 5‐HT Receptor, Alpha and Beta Adrenoreceptor (Subtypes) during Oestrus and Dioestrus in the Bovine Uterus

“…In ruminants like sheep, the 5‐HTR 2 and 5‐HTR 4 mediate the tonic activity of the fore stomach and binding of 5‐HTR 4 agonists provoked excitation (Brikas, 1994; Brikas et al., 1994). In the bovine abomasal antrum, binding of specific respective agonists to 5‐HTR 2 and 5‐HTR 4 receptors was found to increase area under the curve and resting tone in vitro (Spring et al., 2003). Taken together and assuming mRNA abundance mirrors the protein levels, it is likely that 5‐HTR 4 , 5‐HTR 2A , 5‐HTR 2B and 5‐HT 1F , the most expressed 5‐HTR, play an important role in controlling uterine tone in oestrus and dioestrus.…”