Spontaneous in vitro contractile activity of specimens from the abomasal wall of healthy cows and comparison among dairy breeds

Evaluation of differences between breeds for substance P, vasoactive intestinal polypeptide, and neurofilament 200 in the abomasal wall of cattle

OBJECTIVE

To compare the content of substance P, vasoactive intestinal polypeptide, and neurofilament 200 in biopsy specimens taken from the abomasal wall of healthy cows of 2 breeds.

SAMPLE POPULATION

Biopsy specimens taken from different sites of the abomasal wall from 20 German Holstein cows and 20 German Fleckvieh cows.

PROCEDURES

Biopsy specimens were examined immunohistochemically, and the content of substance P, vasoactive intestinal polypeptide, and neurofilament 200 was determined by measuring the immunoreactive areas.

RESULTS

Significant differences between the breeds were detected. Substance P-immuno-reactive area in the corpus abomasi was significantly smaller in the German Holsteins (geometric mean +/- geometric SD, 679 +/- 1.83 microm2) than in the German Fleckvieh cows (1,020 +/- 1.65 microm2). Concerning vasoactive intestinal polypeptide, differences between breeds were not significant. Overall nerve density in the antral abomasal wall was significantly greater in German Holsteins than in German Fleckvieh cows (immunoreactive areas for neurofilament 200 in German Holsteins was 4,842 +/- 1.29 microm2 and in German Fleckvieh cows was 3,333 +/- 1.63 microm2). Conclusions and Clinical Relevance-The significantly lower content of substance P in the corpus abomasi could explain why German Holstein cows are predisposed to abomasal displacement, compared with German Fleckvieh cows, in which this disease is a rare finding.

In vitro effects of cisapride, metoclopramide and bethanechol on smooth muscle preparations from abomasal antrum and duodenum of dairy cows

The objective of this study was to investigate the effects of cisapride (CIS), metoclopramide (MET) and bethanechol (BET) on contractility parameters from smooth muscle preparations of the abomasal antrum and proximal duodenum of cows. Smooth muscle preparations were harvested shortly post-mortem from 42 healthy dairy cows, and concentration-response curves were performed by cumulative application of the drugs. Cisapride and MET did not have any significant effect on the contractility parameters studied, while BET induced a significant, concentration-dependent increase in basal tone (BT), mean amplitude (Amean), and area under the curve (AUC) in smooth muscle preparations from the abomasal antrum, but not from the duodenum. The effect of BET on BT was more pronounced in specimens with longitudinal orientation while the maximal obtainable effect (Vm) in Amean was more pronounced in circular-oriented preparations. Atropine (1 x 10-5 m) significantly inhibited the effect of BET, whereas pre-incubation with hexamethonium or tetrodotoxin (TTX) had no effect, suggesting that the effect was mediated by cholinergic receptors on the smooth muscle. The results may be relevant to diseases or disorders associated with gastric emptying and gastric hypomotility. Further investigations are warranted to investigate the potential ability of BET to enhance abomasal emptying of adult dairy cows.

Modifiers of gastrointestinal motility of cattle

Little clinically relevant, evidence-based data about the effect of motility modifiers on the GI tract of cattle are currently available. Additionally, some of the published results seem to be contradictory. Three main facts explain this apparent discrepancy: (1) Results may not be transferred from one species to another, because presence, concentration, location, distribution, and function of specific receptors may differ significantly among species. (2) The lack of a significant effect on smooth muscle preparations in vitro does not necessarily exclude a certain drug's motility-modifying property on affected animals in vivo. Certain drugs bind to receptors outside the myenteric plexus. Others, such as lidocaine and adrenergic-, dopaminergic-, and opioid-antagonists increase only GI motility, if inhibitory reflexes or a hyperactive state of the inhibitory sympathetic nervous system preexists. (3) Effects of motility modifiers as found in healthy experimental animals in vivo may not be similar to those found in spontaneously diseased animals. Accurate and reliable data on the effect of modifiers of GI motility of cattle will be obtained only from double-blinded, evidence-based, in vivo studies on spontaneously affected animals. Because well-documented results from such studies are extremely rare, intensive research in this field is warranted in the future.

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

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.