Modulation of chewing behavior and reticular pH in nonlactating cows challenged with concentrate-rich diets supplemented with phytogenic compounds and autolyzed yeast.

Feeding of concentrate-rich diets impairs chewing behavior and leads to rumen acidosis in cattle. Because of their modulatory effects on ruminal fermentation, phytogenic compounds (PHY) and autolyzed yeast derivatives (AY) may alleviate the negative consequences of high-concentrate diets. Therefore, this research investigated if chewing behavior and the reticular pH dynamics are modulated by AY and PHY supplementation during repeated concentrate-rich challenges used to simulate intermittent rumen acidotic insults. Eight rumen-cannulated, dry, and nonpregnant Holstein cows were assigned to an incomplete double 4 × 3 Latin square design with 3 treatments and 4 experimental runs (n = 8/treatment). Cows were fed concentrates either not supplemented (CON) or supplemented with PHY or AY. Initially, cows were fed a pure forage diet (FD) and switched to a 65% concentrate diet on DM basis for 1 (CONC 1) and 2 (CONC 2) wk. Between CONC 1 and CONC 2, the cows were fed the FD for 1 wk. Chewing activity was measured using noseband sensors and reticular pH by wireless pH sensors. Data showed that cows spent less time ruminating in CONC 1 than in CONC 2. In agreement, reticular pH drop was more pronounced during CONC 1 than during CONC 2. Cows fed with PHY spent 4 h less with reticular pH <6.0 during CONC 1 and 3 h less with pH <6.0 h in CONC 2 as compared with CON cows. Similarly, PHY supplementation extended rumination time with 88 min/d compared with CON cows during CONC 1. The AY supplementation increased DMI by 20% resulting in a longer eating time compared with CON diet during CONC 1. Enhancement of ruminating by PHY and eating time by AY supplementation resulted in longer total chewing time for PHY (474 min/d) and AY (466 min/d) as compared with CON (356 min/d) in CONC 1. In conclusion, cows experiencing 2 intermittent concentrate-rich challenges increased their ruminating behavior during the second challenge, and this effect was associated with higher reticular pH readings. The PHY supplementation enhanced rumination as well as reticular pH during CONC 1. However, the enhanced pH of cows fed with PHY during CONC 2 was not related to greater rumination, suggesting that influencing factors beyond rumination seemed to play a role in modulating reticular pH in PHY cows during CONC 2. The AY supplementation increased DMI without depressing rumination or reticular pH. Effects of both feed additives were more pronounced during CONC 1 challenge when reticular pH was lower.

Use of dicarboxylic acids and polyphenols to attenuate reticular pH drop and acute phase response in dairy heifers fed a high grain diet.

BACKGROUND: The aim of this study was to determine the ability of two feed additives, a fumarate-malate (FM) and a polyphenol-essential oil mixture (PM), in attenuating the drop of ruminal pH and the metabolic and immune response resulting from an excessively high grain diet. Six heifers were used in a 3 × 3 Latin square experiment and fed a low starch (LS) diet for 14 d, followed by a high starch (HS) diet for 8 d (NDF 33.6%, starch 30.0% DM). In the last 5 days of each period, barley meal was added to decrease rumen pH. During HS feeding all animals were randomly assigned to one of the following three dietary treatments: no supplement/control (CT), a daily dose of 60 g/d of FM, or 100 g/d of PM. Reticular pH was continuously recorded using wireless boluses. On d 21 of each period, rumen fluid was collected by rumenocentesis (1400 h), together with blood (0800 h) and fecal samples (0800, 1400, and 2100 h). RESULTS: The correlation coefficient of pH values obtained using the boluses and rumenocentesis was 0.83. Compared with CT and PM, the FM treatment led to a lower DMI. Nadir pH was lowest during CT (5.40, 5.69, and 5.62 for CT, FM and PM, respectively), confirming the effectiveness of both supplements in reducing the pH drop caused by high grain feeding. This result was confirmed by the highest average time spent daily below 5.6 pH (199, 16 and 18 min/d) and by the highest acetate to propionate ratio of the CT fed heifers. The PM decreased the concentrations of neutrophils (2.9, 3.2, and 2.8 10(9)/L) and acute phase proteins: SAA (37.1, 28.6 and 20.1 µg/mL), LBP (4.1, 3.8, and 2.9 µg/mL), and Hp (675, 695 and 601 µg/mL). Free lipopolysaccharides (LPS) were detected in blood and feces, but their concentrations were not affected by treatments, as the remaining blood variables. CONCLUSIONS: Data suggest that both additives could be useful in attenuating the effects of excessive grain feeding on rumen pH, but the PM supplement was more effective than FM in reducing the inflammatory response compared to CT.

Oxidative stress-induced mitochondrial fragmentation and movement in skeletal muscle myoblasts.

Mitochondria are dynamic organelles, capable of altering their morphology and function. However, the mechanisms governing these changes have not been fully elucidated, particularly in muscle cells. We demonstrated that oxidative stress with H2O2 resulted in a 41% increase in fragmentation of the mitochondrial reticulum in myoblasts within 3 h of exposure, an effect that was preceded by a reduction in membrane potential. Using live cell imaging, we monitored mitochondrial motility and found that oxidative stress resulted in a 30% reduction in the average velocity of mitochondria. This was accompanied by parallel reductions in both organelle fission and fusion. The attenuation in mitochondrial movement was abolished by the addition of N-acetylcysteine. To investigate whether H2O2-induced fragmentation was mediated by dynamin-related protein 1, we incubated cells with mDivi1, an inhibitor of dynamin-related protein 1 translocation to mitochondria. mDivi1 attenuated oxidative stress-induced mitochondrial fragmentation by 27%. Moreover, we demonstrated that exposure to H2O2 upregulated endoplasmic reticulum-unfolded protein response markers before the initiation of mitophagy signaling and the mitochondrial-unfolded protein response. These findings indicate that oxidative stress is a vital signaling mechanism in the regulation of mitochondrial morphology and motility.

Effects and mechanisms of action of the ergopeptides ergotamine and ergovaline and the effects of peramine on reticulum motility of sheep.

OBJECTIVE: To investigate effects and mechanisms of ergotamine and ergovaline and effects of peramine on reticulum motility of sheep. SAMPLE POPULATION: 3 sheep with indwelling electrodes in the reticulum and samples of reticulum collected from 126 sheep at an abattoir. PROCEDURES: In conscious sheep, motility was recorded as integrated electromyograms from the reticulum. Ergotamine was administered IV alone or in combination with the cholinergic muscarinic receptor antagonist atropine to sheep, and motility of the reticulum was assessed. In vitro, whole wall strips of the reticulum, cut in a direction to record longitudinal muscle activity via force transducers, were placed in 10-mL organ baths and superfused with Tyrode Ringer's solution at 37 degrees C and oxygenated with 95% oxygen and 5% carbon dioxide. Testing involved incubation of reticulum strips with ergotamine, ergovaline, and peramine and measurement of motility of the reticulum tissues. RESULTS: Administration of ergotamine to sheep reduced the frequency of reticulum contractions and increased baseline electromyographic activity (tonus). Frequency was unaffected by atropine, whereas tonus was significantly reduced. In vitro, ergotamine and ergovaline increased tonic contractions and stimulated phasic contractions of reticulum tissues and potentiated electrically stimulated contractions. Atropine and tetrodotoxin reduced tonic contractions, but stimulation of large-amplitude phasic contractions remained. Peramine had no effect on motility of reticulum tissues. CONCLUSIONS AND CLINICAL RELEVANCE: Results of the study indicated that peripheral excitatory effects of the ergopeptides on motility of the reticulum appear to be mediated partly through myenteric neurons and muscarinic receptors and also through direct effects on the muscles.

Ultrasonographic assessment of the reticular motility in cows after administration of different doses of metoclopramide and neostigmine.

The aim of the present study was to use of ultrasonography for assessment of reticular motility after administration of various doses of metclopramide and neostigmine in cows. A total of ten Holstein cows were used in six trials in each one single dose of each drug was used. Metoclopramide was used at 0.1, 0.2 and 0.3 mg/kg intramuscularly, whereas neostigmine was used at 0.02, 0.03, and 0.04 mg/kg subcutaneously. Reticular motility was assessed using 3.5 MHz transducer just before drugs administration and every 20 minutes after administration with total time of two hours. At twenty minutes postadministration, metoclopramide at a dose rate of 0.3 mg kg significantly (P<0.01) produced shortening of the interval time between the two biphasic reticular contractions by 25% and significantly (P<0.05) increased the amplitude of the first reticular contraction by 42%, but with mild neurological signs. Neostigmine produced non-significant increase in reticular contraction rate and strength. The results of the present study indicate that metoclopramide and neostigmine at selected doses are not clinically useful agents for increasing reticular contraction rate and strength. The findings of this study in healthy animals may not be extrapolatable to findings in cattle with reticuloruminal hypomotility.

Effects of atropine, scopolamine and xylazine on the placement of an orally administered magnet in cows.

This study was carried out to determine whether the administration of atropine, scopolamine or xylazine to cows before the administration of a magnet orally would help to position it in the reticulum. The transit time of the magnet through the oesophagus was also measured. Sixty Swiss Braunvieh cows were examined by radiography and ultrasonography to locate the reticulum. They were then divided into six groups of 10. Before the administration of the magnet, a control group received 4 ml saline solution subcutaneously, one group received 0.10 mg/kg of atropine subcutaneously, a second received 0.05 mg/kg of atropine intravenously, a third received 0.15 mg/kg of scopolamine intravenously, a fourth group received 0.02 mg/kg of xylazine intravenously, and the cows in the fifth group were positioned so that their forelimbs were 30 cm lower than their hindlimbs during the administration of the magnet. The passage of the magnet through the oesophagus was timed with a stopwatch and monitored with a compass. In the control group the magnet passed through in less than 60 seconds, but in four of the cows receiving either atropine or xylazine intravenously, or having their forelimbs positioned lower than their hindlimbs, it took longer than 60 seconds. In the cows receiving atropine subcutaneously or scopolamine intravenously, it took the same time as in the control group. All the cows were radiographed one-and-a-half hours after the administration of the magnet to determine its location. In seven of the 10 cows in the control group, the magnet was located in the reticulum, but in the other three it was in the cranial dorsal blind sac of the rumen. In the other five groups the magnet was located in the reticulum of between four and seven of the 10 cows, but in the cranial dorsal sac of the rumen, the rumen or in other sites in the other cows.

Tremorgenic mycotoxins increase gastric smooth muscle activity of sheep reticulum and rumen in vitro.

Reticulum and rumen strips (consisting of both muscle layers and the myenteric plexus) were superfused with Tyrode Ringer and their contractions recorded isometrically. The strips were subjected to exogenous acetylcholine and electrical field stimulation (EFS) resulting in contractions that could be blocked by atropine. Responses to the tremorgenic mycotoxin penitrem A and others thought to be involved in ryegrass staggers, paxilline and lolitrem B (10(-10)-10(-6)M), were compared with those of control vehicle (0.1% DMSO). The tremorgens were without effect on quiescent preparations. Penitrem A and paxilline enhanced spontaneously active preparations and the amplitude of contractions in response to EFS. Responses to paxilline had a shorter latency than to penitrem A. Responses of spontaneously active preparations were resistant to atropine. Penitrem A, but not paxilline, increased responses to exogenous acetylcholine. Lolitrem B (10(-6)M) increased responses to EFS, but many responses were equivocal, possibly due to the lower solubility of lolitrem B in aqueous solutions compared to the other tremorgens. The results show that these mycotoxins have peripheral excitatory effects on the reticulorumen and it is suggested that such activity in vivo may reflexly affect centrally derived cyclical contractions.

Ultrasonographic evaluation of reticular motility in cows after administration of atropine, scopolamine and xylazine.

The goal of this study was to evaluate the effect of various dosages and routes of administration of atropine, scopolamine and xylazine on reticular motility in cows. Groups of five cows received atropine, scopolamine or xylazine at dosages varying from 0.01 to 0.20 mg/kg. The drugs were administered intramuscularly and intravenously; atropine was also given subcutaneously. A total of 17 trials, each using five cows, were carried out. Reticular motility was assessed for 3 min immediately prior to the administration of a drug and for 21 min after administration, and the latter period was divided into seven 3-min intervals. The motility was further assessed during 3-min periods every 10 min starting 28 min and ending 141 min after administration of a drug. During each 3-min interval, the number of reticular contractions or the occurrence of reticular atony was determined. Onset and duration of reticular atony were assessed. All three drugs inhibited reticular motility but onset varied with route of administration and dosage. As expected, the onset of reticular atony occurred most rapidly after intravenous administration of each drug, followed by intramuscular and subcutaneous administration. Reticular atony occurred 0-3.0 min after the intravenous administration of each drug and at all dosages except the lowest dosage of atropine. Atony lasted for 3-111 min. Reticular atony occurred 3-18 min and 9-15 min after intramuscular and subcutaneous administration, respectively. It lasted 32-108 min and 39-122 min for the intramuscular and subcutaneous routes, respectively. For each drug, higher dosages resulted in a more rapid onset and longer duration of reticular atony than did lower dosages. This study demonstrated that administration of atropine, scopolamine and xylazine results in reticular atony. Whether this has clinical relevance requires further investigation.

Review: reticuloruminal motility--a pharmacological target with a difference?

The vagal sensory inputs to and motor outputs from the hindbrain gastric centres required for reticuloruminal motility were sampled directly in anaesthetized sheep using electrophysiological 'single fibre' techniques and indirectly in conscious, surgically prepared sheep. Drugs were administered by close-arterial injection into a carotid artery to observe central effects and into the coeliac artery to observe peripheral effects on the reticulorumen. Escherichia coli lipopolysaccharide produced intermediates responsible for the smooth muscle relaxation in the first phase of reticuloruminal stasis and for gastric centre depression in the second phase. Adrenergic influences on reticuloruminal motility comprise (a) an alpha1 adrenoreceptor-induced contracture and raised tension receptor sensitivity, (b) an alpha2 adrenoreceptor-mediated depression of the gastric centres causing stasis, excitation of epithelial receptors evoking rumination, and interference with acetylcholine release in the parasympathetic pathway, (c) abeta1 adrenoreceptor-mediated inhibition of the gastric centres, and (d) abeta2 adrenoreceptor-mediated inhibition of intrinsic and extrinsic motility.

The absorption of calcium ions from the ovine reticulo-rumen.

Net Ca2+ and Mg2+ absorption rates were measured in vivo from buffer solutions placed in the washed reticulo-rumen, isolated in situ in 30 conscious, trained sheep. An increase in concentration of short chain fatty acids (SCFA) in the buffer, over the range 0-50 mM, was shown to stimulate the net rates of absorption of Ca2+ and Mg2+ ions from the rumen. Similarly, the results of in vitro experiments, carried out with ovine rumen epithelium mounted in short-circuited Ussing chambers, showed that the absence of SCFA from the chamber fluid resulted in a reduction in Jnet Ca2+ caused by reduced flux of Ca2+ ions in the mucosal to serosal direction (Jms Ca2+). The addition of 1 mM acetazolamide, an inhibitor of carbonic anhydrase, to the ruminal buffer used in the in vivo experiments led to significant reductions in the net absorption rates of Ca2+ and Mg2+ ions in the presence of SCFA (50 mmol x l(-1)) but not in the absence of SCFA. However, in the in vitro experiments, the addition of 60 microM ethoxyzolamide had no significant effect on Jnet Ca2+. A reduction in pH of the intraruminal buffer in vivo from 6.8 to 5.4 led to significant increases in the net absorption rates of Ca2+ and Mg2+ ions, an effect which was duplicated for Ca2+ in preliminary in vitro experiments in which the pH of the mucosal buffer was reduced from 7.4 to 5.4. This stimulatory effect was confined to Jms Ca2+ and Jnet Ca2+. Ussing chambers were also used to demonstrate that Jnet Ca2+ was reduced by a high transmural potential difference (PD), caused by voltage clamping, independently of the mucosal K+ concentration. Both unidirectional Ca2+ fluxes consisted of a PD-dependent and a K+-insensitive PD-independent component. The latter may be represented by a Ca2+/ 2H+ antiporter. It is postulated that SCFA, and to a lesser extent H2CO3, can stimulate Jms Ca2+ by activation of an apical Ca2+/2H+ antiporter through the provision of protons within the ruminal epithelial cell. A mild reduction in ruminal pH may also lead to a similar stimulation of this putative electroneutral exchange.

Tremorgenic mycotoxins paxilline, penitrem and lolitrem B, the non-tremorgenic 31-epilolitrem B and electromyographic activity of the reticulum and rumen of sheep.

The mycotoxic tremorgens penitrem, paxilline and lolitrem B had profound effects on electromyographic (EMG) activity of smooth muscle of the reticulorumen in conscious sheep, with a similar time course of action to their respective characteristic effects on the induction (1 to 2, 15 to 20 and 20 to 30 minutes) and the duration (1 to 2, 1 to 2 and 8 to 12 hours) of tremoring. Responses to penitrem revealed a greater sensitivity of smooth muscle than skeletal muscle. Effects included an inhibition of the vagally-dependent cyclical A and B sequences of contraction of the reticulorumen, an increase in their amplitude and an excitation of local intrinsic activity contributing to elevated baselines and the occurrence of chaotic activity of the reticulum. The excitatory local effects were partially blocked by atropine, indicating that stimulation of muscarinic cholinoceptors was involved. Increased local activity may mediate a reflex inhibition of cyclical contractions. A non-tremorgenic isomer of lolitrem B (31-epilolitrem B) had no effect on the reticulorumen. The intensity and duration of the effects of lolitrem B, up to 12 hours, indicate that severe disruption of digestion may occur in animals grazing endophyte-infected pasture.

Effects of verapamil, sodium nitroprusside and calcium deprivation on the phenylephrine-induced contraction of smooth muscle strips from the reticular groove of adult cattle.

The effects of verapamil, sodium nitroprusside and calcium deprivation on the smooth muscle strips from the floor of the reticular groove of adult cattle were studied. The mechanical activity of the muscle strip was recorded isometrically. Contraction was induced with phenylephrine (10(-6) mol/l) in Tyrode solution. Verapamil (10(-6) mol/l) produced a high inhibition of the response, phasic and tonic (P < 0.05). Sodium nitroprusside (10(-6) mol/l) reduced mainly the phasic contraction (P < 0.05). Deprivation of Ca2+ from extracellular medium produced a high inhibition of the tonic phase. This study indicates that the action of verapamil on the reticular groove smooth muscle may be partially related to blockade of calcium entry through voltage-dependent channels, opened during phenylephrine stimulation. However, the nitroprusside action could be attributed to effect on the extrusion of calcium.

[Effect of acetazolamide on sodium and potassium absorption in the sheep forestomach]. / Vliianie atsetazolamida na vsasyvanie natriia i kaliia iz predzheludkov ovets.

I.v. Acetazolamide administration suppressed the sodium and potassium absorption up to 90 and 100%, resp., in the sheep reticulo-rumen. Absorption of the short chain fatty acids was not affected. The findings suggest a sodium/potassium exchange processes occurring in the reticulo-rumen epithelium in ruminants.

Endotoxaemia in dairy cattle: mechanism of reticulorumen stasis.

The objective of this study was to determine whether blockade of alpha(-2) adrenergic receptors would restore reticulorumen motility during toxaemia in cows. Reticulorumen contractions were measured via a water-filled balloon connected to a pressure transducer. Intravenous infusion of endotoxin (100 ng kg-1 over 30 min) significantly decreased the number of reticulorumen contractions. Intravenous infusion of yohimbine (125 micrograms kg-1 over 30 min) alone did not affect reticulorumen contractions. However, when yohimbine (125 micrograms kg-1 over 30 min) was infused concurrently with endotoxin (100 ng kg-1 over 30 min), the effects of endotoxin on reticulorumen contraction frequency decreased, suggesting that endotoxaemia causes reticulorumen stasis via a mechanism that involves alpha(-2) adrenergic receptors.

Inhibitory effects of short intravascular infusions of propionate on reticulo-rumen motility in the sheep.

The effect of short infusions into the hepatic portal vein of propionate on reticulo-rumen motility was examined in conscious sheep. Infusions of 10 min duration of propionate at 1-6 mmol.min-1 into the portal vein reduced the frequency and amplitude of reticulum and rumen contractions, especially the amplitude of rumen contractions. Inhibitory effects were not confined to the portal route and were also obtained via the jugular vein, carotid artery, coeliac artery and anterior mesenteric artery. Butyrate was also effective, but acetate much less so and NaCl almost without effect. The inhibitory responses remained after section of nerves to the liver. It appears unlikely the effects reflexly originate from the liver or are derived centrally.

Effects of vasoactive intestinal polypeptide on electromyographic activity of the reticulo-omasal orifice in sheep at two levels of intake.

The effects of intragastric arterial infusions (1 mL/min) of physiological saline, vasoactive intestinal polypeptide (VIP), or VIP-antagonist [4Cl-D-Phe6, Leu17]VIP (1 nmol/mL) on electromyographic (EMG) activities of the reticulum and reticulo-omasal orifice (ROO) in conscious ewes fed to meet either their net energy for maintenance (NEm) or twice maintenance requirements were studied. Intragastric arterial infusions (1 mL/min) of 15-min durations were conducted before, during, and after feeding. The aims of the study were to elucidate the relationships between EMG activities of the reticulum and ROO and their potential regulation by VIP in sheep fed solid feed and how the relationships could be affected by different feeding levels. At both levels of feed intake, reticular EMG spiking activity was associated with high-amplitude EMG spiking activity of the ROO, and lack of spiking activity or quiescence of the ROO was never fully observed until the reticulum became quiescent. Irrespective of feeding level, infusions of VIP were associated with a marked reduction in reticular EMG and ROO spiking activities after 3 to 4 min and a complete cessation of ROO spiking activity 8 min after commencement of VIP infusion. Three to four minutes after initiation of VIP-antagonist infusion, EMG spiking activity of the ROO was enhanced and quiescence of the ROO activity was markedly diminished. The data suggest that 1) VIP may be involved in mediation of quiescence of the ROO and increases the duration of the quiescence in sheep fed at twice maintenance compared with maintenance-fed sheep, 2) the ROO EMG activity is influenced differently by different phases of the feeding cycle, and 3) VIP-antagonist enhances the EMG activity of the ROO.

Influence of closure of the reticular groove on the bioavailability and disposition kinetics of meclofenamate in sheep.

Sodium meclofenamate is a non-steroidal anti-inflammatory drug with anaphylactic protective activity in cattle. The objectives of this study were to describe the pharmacokinetic behaviour of sodium meclofenamate after intravenous and oral administration to sheep and to determine the influence of closure of the reticular groove on the bioavailability of the drug. Sodium meclofenamate was administered by the intravenous (2.2 mg/kg) and oral (20 mg/kg) routes to sheep (n = 6). During the oral study the reticular groove was closed by intravenous administration of lysine vasopressin (0.3 IU/kg) or left open (saline solution). The closure of the reticular groove was assessed by determination of the blood glucose curves after oral administration of a glucose solution. After intravenous administration of meclofenamate, the distribution and elimination half-lives of the drug were 7.2 min and 542 min respectively, Vss was 1.68 L/kg and ClB was 2.47 mliter/min kg. Two different patterns of the plasma concentration curves were observed after oral administration of sodium meclofenamate. When the reticular groove was closed, two peaks were observed (tmax-1 12-15 min, Cmax-1 3.30-24.01 micrograms/mliter; and tmax-2' 52.50-75 min, Cmax-2, 6.45-11.08 micrograms/mliter).

Cholecystokinin does not act on the efferent pathway of cholinergic and adrenergic nerves to inhibit ruminal contractions in sheep (Ovis aries).

The effect of exogenous cholecystokinin-octapeptide (CCK-8) on ruminal contractions and the role of efferent pathways of cholinergic and adrenergic nerves on the effect were studied in sheep. Intravenous infusion of CCK-8 at 11.4 and 45.6 pmol/kg/min significantly inhibited the frequency and amplitude of ruminal contractions in conscious sheep. After bilateral cervical vagotomy, intravenous infusion of CCK-8 at 45.6 mol/kg/min had no detectable effect on amplitude of ruminal contractions induced by electric stimulation to the cervical vagus nerve (1 msec, 20 Hz, 5 mA, for 10 sec at 1-min intervals) in anesthetized sheep. The amplitude of contractile responses of ovine ruminal muscle strips to acetylcholine at 5 x 10(-5) M was not inhibited by CCK-8 applied simultaneously at 1 x 10(-9) M. Intravenous infusion of phentolamine at 53.0 nmol/kg/min, propranolol at 101.4 nmol/kg/min, or their combined infusion did not alter the inhibitory action of CCK-8 at either dose on ruminal contractions in conscious sheep. These results suggest that CCK-8, which does not act on the efferent pathway of cholinergic and adrenergic nerves, may reflexively inhibit reticuloruminal contractions via vagal afferent fibers in sheep.

Effects of verapamil, sodium nitroprusside, tetrodotoxin and caffeine on the electrical transmural stimulation induced contraction in the reticular groove smooth muscle of adult cattle.

The effect of electrical transmural stimulation (ETS) on smooth muscle strips in the floor of reticular groove of adult cattle was studied. The mechanical activity of the muscle strips was recorded isometrically. ETS (4 ms, 5 s, supramaximal voltage) caused frequency dependent (2-30 Hz) contractions of this smooth muscle. An increase in cytoplasmatic free calcium concentration can be achieved by release of the cation from intracellular store sites or by an influx of extracellular Ca2+ through calcium channels. The contractile response of the muscle strips was inhibited about 66% when it was incubated in a calcium-free EGTA-containing solution. The excitatory effect of ETS was not antagonized by verapamil (10(-6) mol/l), sodium nitroprusside (10(-6) mol/l) or tetrodotoxin (10(-6) mol/l). The electrically-evoked contraction was inhibited strongly (92%) by caffeine (30 mmol/l). The contractions of the smooth muscle from the reticular groove smooth muscle are dependent on the concentration of free calcium in the cell cytosol. This response was intracellular Ca2+ ion dependent.

Types of serotonergic receptors involved in the control of reticulo-ruminal myoelectric activity in sheep.

The effects of peripheral (intravenous, i.v.) and central (intracerebroventricular, ICV) administration of agonists of 5-HT1A, 5-HT2, 5-HT3 and 5-HT4 receptors were investigated in conscious sheep chronically fitted with intraparietal electrodes on the reticulum and the dorsal, ventral and caudo-ventral rumen. The 5-HT1A agonist 8-hydroxydipropylaminotetralin increased reticular and decreased ruminal spike burst frequency when given i.v. (80 micrograms/kg) and ICV (8 micrograms/kg). The 5-HT2 and 5-HT3 agonists, alpha-methylserotonin and 2-methylserotonin, induced a moderate inhibition of rumino-reticular contractions when given i.v. at 100 and 150 micrograms/kg, respectively, while marked inhibition was observed after ICV administration at doses of 10 and 5 micrograms/kg, respectively. The 5-HT4 agonist 5-methoxytryptamine strongly stimulated rumino-reticular motility by the ICV (10 micrograms/kg) route, whereas it induced a moderate inhibition when administered i.v. (200 micrograms/kg). The selective antagonist of 5-HT1A, 5-HT2, 5-HT3 and 5-HT4 receptors, spiroxatrine, ritanserin, granisetron and DAU 6285, respectively, blocked the responses of the respective agonists given by the same route. Moreover, the antagonists given ICV blocked the effects of the agonists given i.v. except for DAU 6285 ICV, which did not antagonize the inhibition induced by 5-methoxytryptamine i.v. It is concluded that the four types of serotonergic receptors investigated control rumino-reticular motility at the central level. However, according to the receptor type and the forestomach area (reticulum or rumen) this control may be stimulatory or inhibitory, demonstrating a pleiotropic role of serotonin in the control of rumino-reticular motility in sheep.