Abomasal Antrum Research Articles

Messenger RNA expression and localization of xenin in the gastrointestinal tract in sheep

The present study aimed to determine the primary sequence of ovine xenin and clarify the mRNA expression and peptide localization of xenin in the gastrointestinal tract in sheep. The colocalization of xenin and glucose-dependent insulinotropic polypeptide was also compared in the antrum and duodenum. Analysis of the nucleotide sequence of ovine xenin revealed a high degree (97.9%) of sequence homology of the sequence between sheep and cattle, and the amino acids sequence determined for ovine xenin coincided (100%) with that of other mammalian species. Real-time quantitative PCR for ovine xenin did not show regional difference in the mRNA expression ratio of xenin. In contrast to the real-time quantitative PCR results, anti-xenin positive cells were abundantly localized in the abomasal antrum (P < 0.01) and at a lesser amount in the duodenum, but no antixenin positive cells were observed in the other regions. Anti-xenin single-positive cells were in a majority in the abomasal antrum, whereas anti-xenin single-positive cells, and anti-GIP single-positive cells, and double-positive cells were even colocalized in the duodenum. These results suggest that abomasal antrum is a major source of xenin in the ovine gastrointestinal tract.

The effect of the endotoxemia on the abomasal emptying rate in suckling lambs as shown by acetaminophen absorption test

Abomasal hypomotility and a decreased rate of abomasal emptying are believed to play important roles in the etiopathogenesis of abomasal disorders in ruminants. The abomasal emptying rate is potentially influenced by several factors. Effect of endotoxins on contractility of smooth-muscle preparations from the bovine abomasal antrum has been evaluated, and the results showed that endotoxemia has an inhibitory effect on contractility of abomasal smooth-muscle fibers. To evaluate the effect of the endotoxemia on the abomasal emptying rate in suckling lambs, this study was conducted. This study was done on five suckling lambs in two phases. In phase 1 (control group), the first blood sample was obtained in 7 a.m. (time zero). Then a mixture of milk, barium sulfate 70%, and acetaminophen was administered orally to each lamb. Afterwards, blood samples were obtained each 15 min up to 4 h later. Phase 2 (treatment group) was similar to phase 1, but after the first blood sampling in time zero in 7 a.m., endotoxemia was induced by administration of commercial lipopolysaccharide at dose rate of 2 μg/kg. The rest of the processes of phase 2 were similar to phase 1. Cmax, Tmax, and area under concentration curve (AUC) of acetaminophen were measured in the control and treatment groups. The abomasal emptying rate was assessed by comparing Cmax, Tmax, and AUC of acetaminophen between the control and treatment groups. The data from the control and treatment groups were analyzed statistically by SPSS program, using one-way ANOVA. Results indicated that Cmax, Tmax, and AUC in the endotoxemic (treatment) group were significantly different compared with those in the control group, which means endotoxemia decreased abomasal emptying rate. Results of present study indicated that endotoxemia profoundly decreases the abomasal emptying rate in suckling lambs. Thus, administration of drugs which attenuate endotoxemia could enhance the abomasal emptying rate in endotoxemic animals.

The ‘minute rhythm’ incidence in the ovine abomasal antrum and small intestine

Summary R omanski, K. W., 2016. The ‘minute rhythm’ incidence in the ovine abomasal antrum and small intestine. Bulg. J. Vet. Med ., 19 , No 3, 200 – 208 . To characterise further the ‘minute rhythm’, six healthy rams were equipped with serosal electrodes sewn onto the abomasal antrum and the small bowel. The experiments were performed before and after feeding. Food was o f fered during phase 2a or 2b of the migrating motility complex. The ‘minute rhythm’ incidence and coordination were assessed during four 5 - minute observ ation periods. In the duodenal bulb and duodenum, the pattern was observed more frequently than in other segments e x a mined. During phase 2b, the ‘minute rhythm’ incidence was often more frequent than during phase 2a of the migrating motility complex. Feed ing increased significantly the ‘minute rhythm’ incidence, but these alter a tions were more evident during first two observation periods. In the jejunum, duration of one ‘minute rhythm’ episode was longer than in more proximal segments. In the more distal j ejunal recording site the ‘minute rhythm’ was often absent. The pattern was well coordinated mostly in the antroduodenum and its propagation velocity was the highest also in the upper small bowel. It is co ncluded that the ‘minute rhythm’ incidence, form, a nd coordination depend ed upon the feeding cond itions, intensity of intestinal motility and the gastrointe s tinal segment.

Involvement of neuronal nitric oxide synthase (nNOS) in the regulation of migrating motor complex (MMC) in sheep

The objectives of this study were to evaluate the role of nitric oxide (NO) synthase isoforms (nNOS, eNOS, and iNOS) in the regulation of the migrating motor complex (MMC) in sheep using electromyography and their expression in the gastrointestinal (GI) tract by Western blot (WB) and immunohistochemistry. Intravenous administration of L-NAME or the nNOS inhibitor 7-nitroindazole (7-NI) decreased the MMC interval. Myoelectric activity of intestinal phase II was increased, whereas antral activity was reduced. These effects were blocked by L-arginine. Inhibitors of either iNOS (aminoguanidine and S-methylisothiourea) or eNOS (L-NIO) were ineffective. The NO donor sodium nitroprusside decreased GI myoelectric activity, inhibited the MMC pattern, and prevented the effects induced by L-NAME and 7-NI in the intestine. Intracerebroventricular administration of these agents did not modify GI motility. In the rumen, abomasal antrum, duodenum, and jejunum, WB showed three bands at about 155, 145, and 135kDa corresponding to nNOS, and a 140-kDa band (eNOS); however iNOS was not detected. Positive nNOS immunostaining was observed in neurons of the myenteric and submucous plexus of all GI tissues, while eNOS was found in the endothelial cells, ruminal and intestinal epithelium, as well as in some enteric neurons and in endocrine-like cells of the duodenal Brunner's glands. In contrast, only weak iNOS immunoreactivity was found in ruminal epithelium. Taken together, our results suggest that NO, synthesized at a peripheral level by nNOS, is tonically inhibiting the MMC pattern and intestinal motility in sheep.

Electromyographic study of the abomasal antrum and proximal duodenum in cattle.

Electromyographic study of the abomasal antrum and proximal duodenum in cattle.

Cholecystokinin-dependent selective inhibitory effect on ‘minute rhythm’ in the ovine small intestine

Cholecystokinin (CCK) can exert multiple actions on intestinal motility but its effect on the small-intestinal ‘minute rhythm’ (MR) is virtually unknown. Therefore, the electrical activity from the abomasal antrum, duodenal bulb, duodenum, jejunum and ileum was continuously recorded in six sheep before, during and after slow intravenous administration, of three doses each, of cholecystokinin-octapeptide (CCK-OP) and cerulein. In four of these sheep, two additional electrodes and the strain gauge force transducer were also inserted in the duodenum. Chronic experiments were performed in the fasted and non-fasted animals and saline or CCK peptides were injected during phases 1, 2a or 2b of the duodenal migrating myoelectric complex (MMC). The administration of both CCK peptides in various doses evoked an inhibitory effect mostly in the duodenal bulb, except for the lowest dose of cerulein. The effects of 20 times greater doses of CCK-OP than that of cerulein were more pronounced. The introduction of both CCK peptides during phase 1 of the MMC produced no marked or significant response. In non-fasted animals, the effects of both hormonal peptides, given during phase 2b of the MMC, were often stronger than those given during phase 2a, while in fasted animals the effects of CCK peptides, administered in the course of phases 2a and 2b of the MMC, were similar. Both higher doses of CCK peptides increased the number of spike bursts within the given MR pattern in the duodenum and decreased the incidence of MR mostly in the duodenal bulb. The inhibitory effects of both CCK peptides on the bulbar MR exhibited a dose-response character, though the lowest dose often evoked the slight stimulatory response. It is concluded that CCK principally exerts an inhibitory effect upon the MR in the duodenal bulb and modifies the MR in the duodenum by increasing the spike burst number in a given MR pattern. Both these actions of CCK peptides seem to be physiological. There is a positive relationship between the intensity of the refractory period and the demonstrated effect of CCK in the duodenum.

Role of nitrergic nerves in the regulation of motility of the omasum and abomasum in healthy sheep (Ovis aries)

We examined the physiological role of nitrergic nerves in the regulation of omasal and abomasal motility in conscious healthy sheep and omasal muscle specimens. Nitric oxide (NO)-donor, S-nitroso-acethyl-dl-penicillamine (SNAP, 3-30 nmol/kg per min, i.v.) significantly inhibited omasal electromyographic (EMG) activity, whereas it did not alter EMG activity in the abomasal antrum. However, NO synthase inhibitor, Nomega-nitro-l-arginine-methyl ester (L-NAME, 0.3-3.0 micromol/kg per min, i.v.) did not alter EMG activity of the omasum and abomasum. In the in vitro experiments, SNAP application (6-200 micromol/l) significantly inhibited bethanechol (10 micromol/l)-induced contraction of longitudinal and circular muscles of the omasum. L-NAME application (0.03-3.0 mmol/l) enhanced electric field stimulation-induced contractions of the circular muscles. The results suggest that the omasal muscles are responsive to exogenous NO and that nitrergic nerves innervate the circular muscle layer of the omasum, however, nitrergic nerves are not or scarcely involved the physiological regulation of omasal and possibly abomasal motility in healthy sheep.

New approach to the fed pattern: Feeding evokes the specific spike burst setting in the small bowel of non-fasted sheep

As feeding is not a factor disrupting the migrating motor (myoelectric) complex (MMC) in sheep, it is presumed that the fed pattern is absent in this animal species. In turn, feeding may stimulate ovine gastrointestinal motility. To verify this discrepancy the myoelectric activities of the antrum and duodeno-jejunum were recorded in seven adult sheep. Additionally, the relationship between electrical and mechanical activity was tested in four of these animals by means of strain gauge force transducers mounted near the duodenal electrodes. Chronic experiments were conducted in fasted and non-fasted sheep before, during, and after standard feeding. Fodder was offered during the duodenal phases 1, 2a, or 2b of the MMC. Two types of responses to feeding (an unspecific and a specific fed pattern) were denoted. A simple increase in spike burst intensity, i.e. without their special deployment and assessed as the myoelectric activity index (unspecific fed pattern), was observed in the abomasal antrum and small bowel during and after feeding in the course of phase 2b of the MMC in non-fasted and fasted sheep. In the abomasal antrum its duration was longer than in the small intestine. In non-fasted animals the unspecific fed pattern was more pronounced in the abomasal antrum than in the small bowel, while its duration was longer in fasted animals. The specific fed pattern was evoked in the duodeno-jejunum during feeding initiated in the course of phase 2b of the MMC exclusively in non-fasted animals. During this pattern, the spike burst series were significantly reduced compared with those which appeared during phase 2b of the MMC and dispersed single spike bursts predominated. The average duration of the specific fed pattern was 3–4 min and it arrived 2–7 min after feeding onset. In the remaining periods during feeding, the spike burst pattern resembled that often observed during phase 2b of the MMC. Thus the confined fed pattern is present in sheep and its character depends upon the gastrointestinal region and feeding habits.

Effects of Various Doses of Cholecystokinin Octapeptide and Cerulein on Antral Slow-Wave Frequency and Amplitude in Conscious Sheep

It is suspected that cholecystokinin (CCK) might affect antral slow-wave frequency and amplitude, but in sheep this problem is virtually unknown. Therefore the myoelectric activity was continuously recorded before and after intravenous administration of 0.15 M NaCl or CCK peptides in adult rams, equipped with platinum bipolar electrodes in the abomasal antrum, duodenum, and jejunum. CCK octapeptide (CCK-OP) was given to five rams at doses of 17.5, 175, or 1750 pmol/ kg and cerulein was administered to six rams at doses of 0.735, 7.35, or 73.5 pmol/kg of body weight. Each dose was infused to fasted or non-fasted animals for 30, 60, 120, or 300 s during phase 1, 2a or 2b (the less or more intense) of the migrating myoelectric complex (MMC). The 300-sec infusion of the moderate CCK-OP dose during the less intense or more intense phase 2b of the MMC increased the antral slow-wave amplitude from 79 ± 7 to 124 ± 26 μV (p &lt; 0.01) and from 82 ± 8 to 175 ± 40 μV (p &lt; 0.001), respectively. The 300-sec infusion of the highest CCK-OP dose under the same conditions increased antral slow-wave amplitude from 79 ± 6 to 121 ± 24 μV (p &lt; 0.05) and from 84 ± 9 to 138 ± 27 μV (p &lt; 0.01), respectively. Administration of the moderate dose of CCK for 120 s in the course of the less or more intense phase 2b of the MMC increased antral slow-wave frequency from 6.1 ± 0.2 to 6.6 ± 0.4 cpm (N.S.) and from 6.1 ± 0.3 to 6.8 ± 0.4 cpm (p &lt; 0.05), respectively. Administration of the highest dose of CCK-OP for 120 s in the course of the less or more intense phase 2b of the MMC increased the antral slow-wave frequency from 6.2 ± 0.3 to 7.2 ± 0.4 (p &lt; 0.05) and from 6.0 ± 0.3 to 7.8 ± 0.6 cpm (p &lt; 0.001), respectively. It is concluded that CCK in physiological and putatively pharmacological doses can affect the slow-wave frequency and amplitude in sheep related in part to the small-intestinal MMC phase and the intensity of the antral motor activity.

The effect of cholecystokinin octapeptide upon the migrating myoelectric complex in the ovine small bowel

There is no evident and precise data regarding the effect of cholecystokinin octapeptide (CCK-OP) on the migrating myoelectric complex (MMC) in sheep. Thus, in five rams seven bipolar platinum electrodes were implanted in the abomasal antrum and entire small intestine. The strain gauge force transducer was also attached near the duodenal electrode in three of these animals. During the experiments the myoelectric and motor activity was continuously recorded in fasted and non-fasted sheep. During the recordings two normal consecutive phases 3 of the MMC were recorded. Then, slow injections of CCK-OP of 0.02; 0.2 and 2.0 _g/kg of body weight were given intravenously during phase 1, 2a or 2b of the MMC, identified in the duodenum, until next two consecutive phases 3 MMC were recorded. The moderate dose of CCK-OP administered during phase 2a in non-fasted animals shortened the MMC cycles significantly while the highest dose of the hormone increased the cycle duration and inhibited phase 3 MMC in the duodenum. No such effect was observed in the jejunum. However, duration of phase 3 in this region was decreased mostly by the highest dose of CCK-OP. It can be concluded that CCK inhibits the MMC in ovine small bowel and its effect in the duodenum is most pronounced.

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.

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.

Effects of the mycotoxins lolitrem B and paxilline on gastrointestinal smooth muscle, the cardiovascular and respiratory systems, and temperature in sheep

The mycotoxins lolitrem B (responsible for ryegrass- staggers), and paxilline have a common moiety and are well known for their ability to cause tremoring in animals. Little is known of their other effects in ruminants and we investigated these in sheep, on electromyographic (EMG) activity of gastrointestinal smooth muscle of the reticulum, rumen, abomasal antrum and duodenum and on blood pressure, heart rate, respiration and body temperature. Both mycotoxins induced tremor and caused marked increases in respiratory rate, heart rate and blood pressure, but had relatively little effect on body temperature. Increases in blood pressure preceded substantial rises in heart rate, indicating a peripheral vasoconstrictive effect. Both mycotoxins had variable excitatory and inhibitory effects on the antrum and duodenum, but had consistent and profound effects on activity of the reticulorumen with a similar time course to their characteristic effects for paxilline and lolitrem B respectively, on the induction (2 and 30 minutes) and the duration (2-3 h and 8-12 h) of tremoring. The effects included an inhibition of the vagallydependent cyclical A and B sequences of contraction of the reticulorumen and an excitation of intrinsic activity including "chaotic" activity of the reticulum. Excitatory effects of the tremorgens were partially blocked by atropine, indicating some but not all, excitatory effects on the reticulorumen arise from stimulation of muscarinic cholinoceptors and it is possible this and other excitatory effects may be mediated through calcium-activated high conductance potassium channels. It is concluded tremorgens have widespread effects on the respiratory, cardiovascular and digestive systems. The intensity and duration of the effects with lolitrem B, indicate substantial disruption of digestion may occur with its ingestion on grazing endophyte-infected pasture. Keywords: cardiovascular, electromyograph activity, endophyte, gastrointestinal, lolitrem B, mycotoxins, paxilline, respiration, reticulorumen, temperature

In vitro motility disorders associated with displaced abomasum in dairy cows.

The objective of this study was to investigate in vitro abomasal motility in dairy cows diagnosed with displaced abomasum. Longitudinal muscle myenteric plexus preparations originating from the abomasal antrum of control cows, and cows diagnosed with left displaced abomasum (LDA), right displaced abomasum (RDA) or abomasal volvulus (AV) were used. In control preparations electrical field stimulation evoked an immediate cholinergic contractile response exceeding amplitude of basal contractions by 60%. In contrast, contractile activity was significantly inhibited during electrical stimulation in LDA, RDA and AV by 47%, 66% and 45%, respectively. This inhibition was reversed in the presence of L-NAME. The staining intensity of NADPH-positive myenteric neurones was significantly higher in displaced abomasa than in controls. Concentration-response curves indicated that preparations from displaced abomasa showed reduced sensitivity to acetylcholine. This study demonstrated motility disorders in displaced abomasa in vitro. The results suggested that abomasal displacement is associated with malfunctions at the level of the intrinsic nervous system combined with impaired cholinergic muscle responses. There appeared to be a predominance of nitrergic inhibitory mechanisms over excitatory mechanisms. These results might be of significance for diseases associated with gastric hypomotility and emptying disorders.

Effect of the mycotoxins penitrem, paxilline and lolitrem B on the electromyographic activity of skeletal and gastrointestinal smooth muscle of sheep

The electromyographic ( emg) activity of skeletal muscle was investigated as a method of recording the tremorgenic activity of the mycotoxins penitrem, paxilline and lolitrem B in sheep. emg recordings were made concurrently from the abomasal antrum and duodenum to study the effects of these tremorgens on smooth muscle of the gut. Penitrem (2·2 to 7·5 μg kg −1) induced mild to moderate tremors within 15 to 20 minutes of injection which lasted for two to four hours. Paxilline (0·66 to 1·5 mg kg −1 induced mild to moderate tremors immediately which lasted for one to two hours. Lolitrem B (25 to 110 pg kg −1) had no effect at low doses, but at higher doses it produced tremors appearing over 20 to 30 minutes which persisted for more than 24 hours. The best measure of tremor indicated by skeletal muscle emg was recorded from the shoulder area. The responses of smooth muscle of the antrum and duodenum to the tremorgens were variable. They included inhibitory effects on the antrum but no stimulation. The tremorgens had inhibitory effects on the duodenum on some occasions but on others, phase III migrating myoelectric complex-like activity was stimulated.

Effects of 5-hydroxytryptamine agonists on myoelectric activity of the forestomach and antroduodenal area in sheep.

To increase knowledge of the role of 5-hydroxytryptamine (5-HT) receptors in the regulation of reticuloruminal, omasal and antroduodenal myoelectric activity in sheep, the effects of 5-HT agonists on forestomach and antroduodenal myoelectric activity have been investigated in conscious sheep. 5-Carboxamidotryptamine, methysergide, alpha-methyl-5-HT, 2-methyl-5-HT, cisapride, zacopride or metoclopramide were infused intravenously for 5 min and myoelectric recordings were obtained from electrodes chronically implanted in the reticulum, rumen (dorsal sac), omasal body, abomasal antrum and duodenal bulb. The integrated activity of the reticular and ruminal spike bursts was modified only by the highest doses of alpha-methyl-5-HT, 2-methyl-5-HT, metoclopramide and cisapride. A phase III-like activity pattern was recorded in the antroduodenal area with all 5-HT-ergic agents and a dose-dependent inhibition of myoelectric activity was recorded in both reticulorumen and omasum at the same time as the antroduodenal effects. In the forestomach, methysergide alone induced inhibition of ruminal secondary contractions; 5-HT, alpha-methyl-5-HT, cisapride and metoclopramide, moreover, evoked an initial dose-dependent increase in antral activity. These results suggest that 5-HT1, 5-HT2, 5-HT3 and 5-HT4 receptors are involved in the regulation of the migrating myoelectric complex in sheep and in the genesis of forestomach hypomotility that is occasionally recorded concomitantly with the spontaneous duodenal phase III in sheep. 5-HT4 receptors also have a prokinetic action in the antral area.

Investigations on etiology and pathogenesis of abomasal displacement in adult cattle

Heritability of abomasal displacement was estimated in 30 Friesian herds in Germany using similarity between mothers and daughters. Four-point correlation coefficients were calculated from quadrant squares. The h2 of abomasal displacement was estimated to be 0.24. Milk composition analysis was used to indicate an energy deficit in the diet (fat:protein ratio &gt;1.4) and indicated that cows in 27 herds in which abomasal displacement occurred (case herds) had not received energy-rich carbohydrates in the diets unlike 27 herds in which abomasal displacement was not diagnosed (control herds). In herds where abomasal displacement occurred the high fat:protein ratio in the milk was found in the year before abomasal displacement was diagnosed, and was significantly higher than in the control herds. The fat:protein ratio also tended to be high in the month before abomasal displacement occurred. This indicates that herds in which abomasal displacement occurred received less energy-rich carbohydrates than herds in which displacement was not diagnosed. In vitro studies on muscle strips from the abomasal antrum of healthy cows and cows with abomasal displacement indicated that muscle activity was inhibited during abomasal displacement due to lack of cholinergic excitation and/or predominance of nitroxergic inhibition.

Vagal reflex inhibition of motility in the abomasal body of sheep by antral and duodenal tension receptors.

Vagally-mediated regulation of motility in the abomasal body by duodenal and abomasal antral motility was demonstrated in acutely prepared anaesthetized sheep. The enteric plexuses between the abomasal body, antrum and duodenum were interrupted by transection. Antral contractions were more effective than duodenal contractions at causing inhibition of the abomasal body, and antral isometric conditions were more effective than antral isotonic conditions. Inhibition of motility in the abomasal body was reduced by unilateral cervical vagotomy, was abolished by bilateral cervical vagotomy, and was reversibly inhibited by cervical vagus cold block. The demonstration of vagal pathways in abomaso-abomasal reflexes confirms a functional homology of the mechanisms in the ruminant and animals with simple forms of stomach.

Electrophysiological characteristics of tension receptors in the abomasal antrum of sheep.

Unitary impulse activity from tension receptors in the abomasal antrum in sheep anaesthetized with chloralose was studied with concurrent measurements of isometric tension in the antral wall, intraluminal pressures and electromyography (EMG). Rhythmical background activity had a close correlation with intraluminal pressure changes and usually a close correlation with local increases in EMG activity and isometric tension. Impulse frequencies increased, but were not sustained, following changes from isotonic to isometric conditions. Tension receptors were excited by transmural compression, by antral distension and by local intra-arterial injections of acetylcholine (2.5-25 micrograms), pentagastrin (10-20 micrograms), 5-hydroxytryptamine (1-20 micrograms), adrenaline (10 micrograms) cholecystokinin-8 (1-5 micrograms) or bradykinin (0.5-20 micrograms), and by systemic injections of bethanecol (5-1000 micrograms). Local intra-arterial perfusions of atropine (50 micrograms) and hexamethonium (100 micrograms) did not abolish spontaneous antral movements or affect the enhanced impulse activity evoked by acetylcholine or 5-hydroxytryptamine. Most antral tension receptors were excited by increases in antral tension or passive distension; they therefore functioned 'in series' with the muscularis externa. The discharges of three tension receptors were 'off-loaded' early during the contraction evoked by local injections of pentagastrin (10-20 micrograms).

Low tissue gastrin content in the ovine distal duodenum is associated with increased percentage of G34

1. 1. In adult sheep and in lambs, over 95% of gastrin in the abomasal antrum was G17 with small amounts of G34 and lesser amounts of Component I. 2. 2. Low gastrin concentration in the proximal duodenum was associated with a reduced percentage of G17. 3. 3. The proportion of G34 increased progressively down the duodenum from a mean of 7% proximally to 47% in the most distal segment, and correlated negatively in any segment with the gastrin content. 4. 4. In both the antrum and proximal duodenum, 60–70% of the G17 was in the sulphated form. 5. The gastroepiploic venous serum contained less G17 and more G34 than the tissues and up to 19% G14.