Chitosan-based nanocomposites for the repair of bone defects.

Chitosan scaffolds of different deacetylation degrees, average molecular weights and concentrations reinforced with silica nanoparticles were prepared for bone tissue regeneration. The resulting nanocomposites showed similar pore sizes (<300 µm) regardless the deacetylation degree and concentration used in their formulation. Their mechanical compression resistance was increased by a 30% with the addition of silica nanoparticles as nanofillers. The biocompatibility of the three-dimensional chitosan scaffolds was confirmed by the Alamar Blue assay in human primary osteoblasts as well as the formation of cell spheroids indicative of their great potential for bone regeneration. In vivo implantation of the scaffolds in a mice calvaria defect model provided substantial evidences of the suitability of these nanocomposites for bone tissue engineering showing a mature and dense collagenous tissue with small foci of mineralization, vascularized areas and the infiltration of osteoblasts and osteoclasts. Nevertheless, mature bone tissue formation was not observed after eight weeks of implantation.

Peptic Ulcer Bleeding Risk. The Role of Helicobacter Pylori Infection in NSAID/Low-Dose Aspirin Users.

OBJECTIVES: Helicobacter pylori (H. pylori) infection and NSAID/low-dose aspirin (ASA) use are associated with peptic ulcer disease. The risk of peptic ulcer bleeding (PUB) associated with the interaction of these factors remains unclear. The objective of this study was to determine the risk of PUB associated with the interaction between H. pylori infection and current nonsteroidal anti-inflammatory drugs (NSAIDs) or low-dose ASA use. METHODS: This was a case-control study of consecutive patients hospitalized because of PUB. Controls were matched by age, sex, and month of admission. H. pylori infection status was determined in all cases and controls by serology. Drug use was determined by structured questionnaire. Adjusted relative risk (RR) associated with different factors, and the interaction between NSAID/ASA and H. pylori infection was estimated by logistic regression analysis. RESULTS: The study included 666 cases of PUB and 666 controls; 74.3% cases and 54.8% controls (RR: 2.6; 95% confidence interval (CI): 2.0-3.3) tested positive for H. pylori infection; 34.5% of cases had current NSAID use compared with 13.4% of controls (RR: 4.0; 95% CI: 3.0-5.4). Respective proportions for low-dose ASA use were 15.8 and 12%, respectively (RR: 1.9; 95% CI: 1.3-2.7). The RR of PUB for concomitant NSAID use and H. pylori infection suggested an additive effect (RR: 8.0; 95% CI: 5.0-12.8), whereas no interaction was observed with ASA use (RR: 3.5; 95% CI: 2.0-6.1). CONCLUSIONS: NSAID, low-dose ASA use, and H. pylori infection are three independent risk factors for the development of PUB, but there were differences in the interaction effect between low-dose ASA (no interaction) or NSAID (addition) use and H. pylori infection, which may have implications for clinical practice in prevention strategies.

Chitosan derivatives as nanocarriers for hLDHA inhibitors delivery to hepatic cells: A selective strategy for targeting primary hyperoxaluria diseases.

Primary hyperoxalurias (PHs) are a group of inherited alterations of the hepatic glyoxylate metabolism that result in an excess of oxalate production by the oxidation of glyoxylate by the human lactate dehydrogenase A enzyme (hLDHA). The selective liver inhibition of this enzyme is one of the therapeutic strategies followed in the treatment of this disease. Even though several efforts have been recently performed using gene silencing by the RNA interference approach, small-molecule inhibitors that selectively reach hepatocytes are preferred since they present the advantages of a lower production cost and better pharmacological properties. In that sense, the design, synthesis, and physicochemical characterization by NMR, FTIR, DLS and TEM of two nanocarriers based on chitosan conjugates (1, non-redox-sensitive; 2, redox-sensitive) have been performed to (i) achieve the selective transport of hLDHA inhibitors into hepatocytes and (ii) their disruption once they reach the hepatocytes cytosol. Polymer 2 self-assembled into micelles in water and showed high drug loadings (19.8-24.5 %) and encapsulation efficiencies (31.9-40.8%) for the hLDHA inhibitors (I-III) tested. The non-redox-sensitive micelle 1 remained stable under different glutathione (GSH) concentrations (10 µM and 10 mM), and just a residual release of the inhibitor encapsulated was observed (less than 10 %). On the other hand, micelle 2 was sufficiently stable under in vitro physiological conditions (10 µM, GSH) but it quickly disassembled under the simulated reducing conditions present inside hepatocytes (10 mM GSH), achieving a 60 % release of the hLDHA inhibitor encapsulated after 24 h, confirming the responsiveness of the developed carrier to the high levels of intracellular GSH.

Reticulated vitreous carbon: a useful material for cell adhesion and tissue invasion.

Diverse carbon materials have been used for tissue engineering and clinical implant applications with varying success. In this study, commercially available reticulated vitreous carbon (RVC) foams were tested in vitro and in vivo for compatibility with primary cell adhesion and tissue repair. Pores sizes were determined as 279 ± 98 µm. No hydroxyapatite deposition was detected after immersion of the foams in simulated body fluid. Nonetheless, RVC provided an excellent support for adhesion of mesenchymal stem cells (MSCs) as well as primary chondrocytes without any surface pre-treatment. Live cell quantification revealed neutral behaviour of the material with plastic adhered chondrocytes but moderate cytotoxicity with MSCs. Yet, rabbit implanted foams exhibited good integration in subcutaneous pockets and most importantly, total defect repair in bone. Probably due to the stiffness of the material, incompatibility with cartilage regeneration was found. Interestingly and in contrast to several other carbon materials, we observed a total lack of foreign body reactions. Our results and its outstanding porous interconnectivity and availability within a wide range of pore sizes convert RVC into an attractive candidate for tissue engineering applications in a variety of bone models and for ex vivo cell expansion for regenerative medical applications.

Promoting bioengineered tooth innervation using nanostructured and hybrid scaffolds.

The innervation of teeth mediated by axons originating from the trigeminal ganglia is essential for their function and protection. Immunosuppressive therapy using Cyclosporine A (CsA) was found to accelerate the innervation of transplanted tissues and particularly that of bioengineered teeth. To avoid the CsA side effects, we report in this study the preparation of CsA loaded poly(lactic-co-glycolic acid) (PLGA) nanoparticles, their embedding on polycaprolactone (PCL)-based scaffolds and their possible use as templates for the innervation of bioengineered teeth. This PCL scaffold, approved by the FDA and capable of mimicking the extracellular matrix, was obtained by electrospinning and decorated with CsA-loaded PLGA nanoparticles to allow a local sustained action of this immunosuppressive drug. Dental re-associations were co-implanted with a trigeminal ganglion on functionalized scaffolds containing PLGA and PLGA/cyclosporine in adult ICR mice during 2weeks. Histological analyses showed that the designed scaffolds did not alter the teeth development after in vivo implantation. The study of the innervation of the dental re-associations by indirect immunofluorescence and transmission electron microscopy (TEM), showed that 88.4% of the regenerated teeth were innervated when using the CsA-loaded PLGA scaffold. The development of active implants thus allows their potential use in the context of dental engineering. STATEMENT OF SIGNIFICANCE: Tooth innervation is essential for their function and protection and this can be promoted in vivo using polymeric scaffolds functionalized with immunosuppressive drug-loaded nanoparticles. Immunosuppressive therapy using biodegradable nanoparticles loaded with Cyclosporine A was found to accelerate the innervation of bioengineered teeth after two weeks of implantation.

PGE(2) receptors and their intracellular mechanisms in rabbit small intestine.

The effects of PGE(2) on longitudinal smooth muscle, the intracellular mechanisms involved, and the localization of EP receptors were investigated in rabbit small intestine. PGE(2) evoked contractions in small intestine that were reduced by tetrodotoxin and hexamethonium. 17-Phenyl trinor PGE(2), sulprostone, misoprostol and 16,16-dimethyl PGE(2) evoked contractions. Butaprost did not modify spontaneous motility. AH 6809 reduced PGE(2) and 17-phenyl trinor PGE(2)-induced contractions. Verapamil, Ca(2+) free medium, staurosporine, forskolin, theophylline, and rolipram diminished, while IP-20 and H-89 increased PGE(2)-induced contractions. Western blot analysis showed protein bands of 41kDa for EP(1), 71kDa for EP(2) and 62kDa for EP(3) receptors. EP(1), EP(2) and EP(3) receptors were detected in neurons of the myenteric and submucosal ganglia, but only EP(3) receptors were found in smooth muscle layers. This study did not detect EP(4) receptor. PGE(2)-induced contractions would be mediated through EP(1) and EP(3) receptors, and voltage-dependent Ca(2+) channels, protein kinase C, and cAMP would be implicated in these responses.

The role of tyrosine kinase in prostaglandin E2 and vanadate-evoked contractions in rabbit duodenum in vitro.

Prostaglandin E2 (PGE2) can interact with at least four cell surface receptors (EP1-EP4) in smooth muscle, which evokes a variety of intracellular responses depending on the G protein to which the cell surface receptors are coupled. The activation of G protein-coupled receptors and receptor tyrosine kinases can lead to the phosphorylation of tyrosine residues of various cellular proteins. The aim of this study was to examine the role of tyrosine phosphorylation in PGE2, vanadate and carbachol-evoked contractions. PGE2, vanadate, and carbachol induced contractile motor responses in the longitudinal smooth muscle of rabbit duodenum. PGE2-evoked contractions decreased in the presence of genistein or tyrphostin B44. PGE2-evoked contractions increased in the presence of vanadate. Vanadate-evoked contractions decreased in the presence of genistein. In contrast, tyrphostin 47 increased the vanadate-evoked contractions. Vanadate-evoked contractions were reduced in the presence of Ca2+-free solutions, verapamil, or indomethacin. U-73122 decreased PGE2-evoked contractions. Carbachol-evoked contractions decreased in the presence of genistein, tyrphostin B44 or tyrphostin 47. Our results suggest that PGE2, vanadate or carbachol-evoked contractions are mediated by protein tyrosine phosphorylation. Protein tyrosine phosphorylation might cause an increase in calcium influx through voltage-dependent channels and the release of prostaglandins in the longitudinal smooth muscle of the rabbit duodenum.

K+ channels involved in contractility of rabbit small intestine.

Most excitable cells, including gastrointestinal smooth muscle cells, express several types of K+ channels. The aim of this study was to examine the types of K' channels involved in the contractility of longitudinal smooth muscle of rabbit small intestine in vitro. Spontaneous contractions and KCl-stimulated contractions were reduced by atropine, phentolamine, propranolol, suramin, tetrodotoxin and indomethacin. The amplitude and tone of spontaneous contractions were increased by apamin, charybdotoxin, iberiotoxin, E4031, tetraetylammonium (TEA) and BaCl2. The frequency of contractions was reduced in the presence of apamin and TEA and increased by charybdotoxin. It was found that 4-aminopyridine increased the tone of spontaneous contractions and reduced the amplitude and frequency of contractions. Glibenclamide did not modify the amplitude, frequency or tone of contractions. KCl-stimulated contractions were increased by E4031, were not modified by apamin, glibenclamide, NS1619 or diazoxide, and were reduced by charybdotoxin, TEA, 4-aminopyridine or BaCl2. These results suggest that both Ca2+-activated K+ channels of small and high conductance, and HERG K+ channels and inward rectifier K+ channels participate in spontaneous contractions of small intestine. On the other hand, voltage-dependent K+ channels, HERG K+ channels, inward rectifier K+ channels and high conductance Ca2+-activated K+ channels are involved in KCl-stimulated contractions.

The role of NO in the contractility of rabbit small intestine in vitro: effect of K+ channels.

Nitric oxide (NO) is an inhibitory neurotransmitter of intestinal smooth muscle cells. The aim of this study was to determine the role of NO in the contractility of rabbit small intestine smooth muscle in vitro. The amplitude, frequency and tone of spontaneous contractions in longitudinal and circular smooth muscle of duodenum, jejunum and ileum were determined and the sodium nitroprusside (SNP), acetylcholine (ACh) and KCl responses were quantified. L-NAME, L-NNA, L-arginine and D-arginine did not affect the amplitude, frequency and tone of spontaneous contractions. ODQ (10(-6) M) increased the tone of spontaneous contractions of the types of tissues examined, and the amplitude in ileum, without modifying the frequency. SNP (10(-4) M) evoked relaxations that were not influenced by atropine (10(-6) M) plus guanethidine (10(-6) M), apamin (10(-8) M) or glybenclamide (10(-6) M), but were increased by TTX (10(-6) M) and verapamil (10(-7) M). SNP-induced relaxations were reduced by charybdotoxin (10(-8) M) and ODQ (10(-6) M). ODQ (10(-5) M) reduced ACh-induced contractions, but it did not influence KCl-evoked contractions. Those results suggest that NO modulates the spontaneous contractions of small intestine in rabbits. This effect is mediated by cGMP and Ca2+-dependent K+ channels of large conductance.

Evidence for the involvement of 5-HT4 receptors in the 5-hydroxytryptamine-induced pattern of migrating myoelectric complex in sheep.

1. The effects induced by 5-hydroxytryptamine (5-HT) on gastrointestinal myoelectric activity in conscious sheep were recorded through electrodes chronically implanted and analysed by computer. The 5-HT receptors and the cholinergic neuronal pathways involved in these actions were investigated. 2. The intravenous (i.v.) administration of 5-HT (2, 4 and 8 micrograms kg-1 min-1, 5 min) induced an antral inhibition concomitant with a duodenal activity front that migrated to the jejunum, followed by a period of intestinal inactivity. This myoelectric pattern closely resembled that observed in the phases III and I of the migrating myoelectric complex (MMC) in sheep. The 0.5 microgram kg-1 min-1 dose evoked the same pattern in only two out of the six animals used. Likewise, the 1 microgram kg-1 min-1 dose similarly affected four of the six animals. In addition, a transient stimulation was observed in the antrum and jejunum when the two highest doses were used. 3. The 5-HT1 antagonist, methiothepin (0.1 mg kg-1), the 5-HT2 antagonists, ritanserin (0.1 mg kg-1) and ketanserin (0.3 mg kg-1), the 5-HT3 antagonists, granisetron (0.2 mg kg-1) and ondansetron (0.5 mg kg-1), as well as the 5-HT4 antagonist, GR113808 (0.2 mg kg-1), did not modify the spontaneous gastrointestinal myoelectric activity. However, the cholinoceptor antagonists, atropine (0.2 mg kg-1) and hexamethonium (2 mg kg-1), inhibited gastrointestinal activity. 4. When these antagonists were injected i.v. 10 min before 5-HT (2 or 4 micrograms kg-1 min-1, 5 min), only GR113808, atropine and hexamethonium were able to modify the 5-HT-induced actions, all of them being completely blocked by the three antagonists. 5. Our data show that 5-HT initiates a MMC-like pattern in the gastrointestinal area in sheep through 5-HT4 receptors. Furthermore, these actions are mediated by cholinergic neural pathways involving muscarinic and nicotinic receptors. However, our results do not indicate a role for either 5-HT1, 5-HT2 or 5-HT3 receptors in the 5-HT-induced effects.

Effect of motilin on gastrointestinal myoelectric activity in conscious rabbits.

Gastrointestinal myoelectric activity was investigated in conscious rabbits with chronically implanted electrodes. As rabbit stomach is never empty, food was removed 1 h before the beginning of recordings. Propagated activity fronts spontaneously started in the jejunum without associated changes in the antroduodenal area. Intravenous administration of either motilin (600-1500 ng/kg) or erythromycin (5-50 micrograms/kg) did not modify antral activity, but simultaneously increased duodenal and jejunal activity in a dose-dependent manner. Spontaneous and induced jejunal activity fronts showed some similarities. However, those induced did not propagate and were not followed by a quiescence period. The effects of motilin (900 ng/kg) and erythromycin (25 micrograms/kg) were resistant to atropine (0.5 mg/kg), hexamethonium (2 mg/kg), or ondansetron (0.5 mg/kg). These results suggest that motilin is not a physiological modulator of the migrating myoelectric complex (MMC) in rabbits. Moreover, neither cholinergic nor 5-HT3 receptors are involved in either motilin or erythromycin-induced actions.

Effect of lipopolysaccharide on rabbit small intestine muscle contractility in vitro: role of prostaglandins.

The purpose of this study was to investigate the effect of lipopolysaccharide (LPS) on spontaneous contractions and acetylcholine (ACh) induced contractions of rabbit intestinal segments in vitro, with two different protocols: intestinal segments isolated from LPS-treated rabbits and intestinal segments incubated with LPS. The frequency of spontaneous movements decreased significantly in LPS-treated rabbits at 2 microg kg-1 in the duodenum and 20 microg kg-1 in the duodenum, jejunum and ileum. LPS (0.2 microg kg-1) reduced significantly the ACh contractions (10-6 mol L-1) in the duodenum (61%), jejunum (48%) and ileum (21%). Indomethacin (1, 5 and 10 mg kg-1) administered 15 min before LPS (0.2 microg kg-1) antagonized the LPS effects on the ACh-induced contractions. Prostaglandin (PG)E2 (8 microg kg-1) inhibited significantly the frequency of spontaneous contractions in the ileum and reduced the ACh-induced contractions in the three segments, mimicking the LPS effects. The amplitude and frequency of contractions in rabbit intestinal segments previously incubated with LPS (0.03, 0.3, 3 and 30 microg mL-1) were not modified with respect to the control. The ACh-induced contractions (10-4 mol L-1) were significantly reduced after 90 min of incubation with LPS. The inhibition of LPS (0.3 microg mL-1) was 43% in the duodenum, 35% in the jejunum and 17% in the ileum. Indomethacin added before LPS blocked the effect of LPS on the ACh-induced contractions in the duodenum, jejunum and ileum. These results show that LPS decreases intestinal contractility in rabbits and suggest that PGs are implicated in these actions.

Central tumour necrosis factor-alpha mediates the early gastrointestinal motor disturbances induced by lipopolysaccharide in sheep.

Cytokines are involved in fever and other symptoms of the acute phase response induced by endotoxins. The aim of this work was to study the involvement of central tumour necrosis factor-alpha (TNF-alpha) in the changes induced by lipopolysaccharide (LPS) on gastrointestinal (GI) motility in sheep. Body temperature and myoelectric activity of the antrum, duodenum and jejunum was recorded continuously. Intravenous (i.v.) administration of LPS (0.1 micro g kg-1)-induced hyperthermia, decreased gastrointestinal myoelectric activity and increased the frequency of the migrating motor complex (MMC). These effects started 40-50 min after LPS and lasted for 6-7 h. TNF-alpha (50 and 100 ng kg-1) mimicked these effects when injected intracerebroventricularly (i.c.v.) but not i.v. Pretreatment with soluble recombinant TNF receptor (TNFR:Fc, 10 micro g kg-1, i.c.v.) abolished the TNF-induced actions and reduced those evoked by LPS. Furthermore, the effects induced by either LPS or TNF were suppressed by prior i.c.v. injection of indomethacin (100 micro g kg-1). In contrast, the i.v. injections of TNFR:Fc or indomethacin were ineffective. Our data suggest that LPS disturbs GI motility in sheep through a central pathway that involves TNF-alpha and prostaglandins sequentially.

Action of robenidine on the intestinal transport and digestion of nutrients in rabbit.

Robenidine is an anticoccidial guanidine used as an additive in rabbit fodder. Because its action is restricted to the small intestine, the present work addresses the question whether robenidine affects the growth of the animals, sugar and amino acid intestinal transport and membrane-bound intestinal digestion. For this purpose we have determined the intestinal transport of the substrates, and the enzymatic activity of neutral aminopeptidase and sucrase. We have found that robenidine diminishes the tissue accumulation of L-leucine and D-galactose at long incubation times, and increases the transepithelial mucosal to serosal flux of both substrates. These results suggest that robenidine may stimulate the enterocyte basolateral membrane flux of sugars and neutral amino acids. These results have been corroborated by means of isolated brush border and basolateral membrane vesicles. Apart from these effects, robenidine has also been shown to increase the enzymatic activity of neutral aminopeptidase and sucrase and thus resulting in a better digestion of nutrients.

Effect of motilin, somatostatin and bombesin on gastroduodenal myoelectric activity in sheep.

The effects of motilin, erythromycin, somatostatin and bombesin on antroduodenal myoelectric activity were investigated in conscious sheep. Myoelectric recordings were obtained from electrodes chronically implanted on the antrum and duodenal bulb. Peptides or erythromycin were infused intravenously (i.v.) during 5 min. Antagonists were injected i.v. as a bolus. Neither motilin (2.5-80 ng/kg/min) nor erythromycin (2-16 micrograms/kg/min) modified the antroduodenal myoelectric activity, although a single bolus of these compounds (250 ng/kg and 50 micrograms/kg respectively) increased the antral activity. Somatostatin at 5 ng/kg/min induced a decrease in the myoelectric activity of antrum and duodenum. However, doses of 10 to 40 ng/kg/min evoked a duodenal phase III-like activity with a subsequent quiescence period and a concomitant inhibition of the antral activity. These effects were reproduced by bombesin (2.5 to 40 ng/kg/min). Furthermore, an initial increase in the myoelectric activity and in the frequency of slow waves were recorded in the antrum when the highest doses were used. On the other hand, atropine (0.2 mg/kg) or hexamethonium (2 mg/kg) caused a long-lasting inhibition of antroduodenal myoelectric activity. These cholinergic antagonists abolished the effects induced by somatostatin (20 ng/kg/min) but not those evoked by bombesin but not motilin are putative modulators of the migrating myoelectric complex (MMC) in sheep. Moreover, a cholinergic neural pathway is involved in the somatostatin but not in the bombesin-induced effects.

Involvement of somatostatin, bombesin and serotonin in the origin of the migrating myoelectric complex in sheep.

Antroduodenal myoelectric activity was recorded in conscious sheep by electrodes chronically implanted in the muscular wall. Furthermore, plasma immunoreactive (i.r.) motilin, somatostatin and bombesin concentrations were determined by RIA. The intravenous infusion of somatostatin (20 ng/kg/min), bombesin (10 ng/kg/min) or serotonin (5-HT, 4 micrograms/kg/min) for 5 min, induced a duodenal myoelectric activity front followed by a period of quiescence. These duodenal events were concomitant with an antral inhibition. This pattern resembled that observed in a spontaneous migrating myoelectric complex (MMC) in sheep. Bombesin and 5-HT evoked an additional and transient increase in antral activity simultaneously with the duodenal activity front. On the other hand, plasma i.r. motilin levels did not show any fluctuations during spontaneous MMC cycles or after somatostatin, bombesin or 5-HT infusions. Likewise, plasma i.r. bombesin levels remained unchanged during spontaneous MMC or after administration of somatostatin. However, 5-HT -induced duodenal activity fronts were closely associated with a sharp peak in plasma i.r. bombesin. Finally, plasma i.r. somatostatin concentrations rose at the end of spontaneous phase III and peaked in phase I. A similar pattern of somatostatin release in plasma was found while the duodenal activity front and quiescence period developed after either 5-HT or bombesin infusions. These results do not indicate a role for motilin in the control of MMCs in sheep, although a definitive conclusion cannot be drawn until synthetic sheep motilin is available. However, our data suggest that somatostatin and bombesin-like peptides as well as 5-HT, acting in a coordinated manner, could be involved in the regulation of cyclical antroduodenal motor events in sheep.

The role of Ca2+ in the contractility of rabbit small intestine in vitro.

This study evaluated the role of Ca2+ in spontaneous and ACh- and KCl-induced contractions in longitudinal and circular smooth muscle from rabbit small intestine in vitro. In the first experiment, the amplitude, frequency and tone of spontaneous contractions in longitudinal and circular smooth muscle of small intestine were determined and, in the second experiment, the ACh- and KCl-induced responses of longitudinal and circular smooth muscle were measured. Atropine and guanethidine reduced the amplitude and tone of contractions in longitudinal and circular muscle, but reduced the frequency of contractions in circular muscle, only. TTX attenuated the amplitude of contractions and decreased the tone of contractions in longitudinal muscle, but increased the tone in circular muscle. Ca2+-free solutions, verapamil, nifedipine and caffeine diminished the three parameters of spontaneous contractions. Thapsigargin and cyclopiazonic acid increased the amplitude and tone of contractions in ileum longitudinal muscle, only, and cyclopiazonic acid increased the amplitude of contractions in circular muscle. Ca2+-free solutions, verapamil, nifedipine, thapsigargin, cyclopiazonic acid, and caffeine diminished ACh- and KCl-induced contractions. Those results suggest that extracellular Ca2+ plays a role in spontaneous contractions, and extracellular and intracellular Ca2+ participate in the ACh- and KCl-induced contractions of rabbit small intestine.

Effects of nicarbazin on intestinal digestion and absorption of nutrients in the rabbit.

Nicarbazin is an anticoccidial drug, used mainly in birds, which has shown several other effects including inhibition of growth and feed efficiency in poultry, and stimulation of sugar and amino acid intestinal absorption in rabbit. The present work was designed to determine whether nicarbazin added to the feed, affects growth and feed intake in rabbit, and whether the continuous ingestion of nicarbazin can alter the mechanisms of intestinal nutrient absorption or digestion in this species. Nicarbazin, administered at the recommended dose (125 ppm) had no harmful effects either on growth or on feed intake of animals. After treatment for one month with nicarbazin at the dose of 125 ppm added to the feed, rabbits displayed a higher transport ability of both D-glucose and L-leucine through the enterocyte plasma membranes than did untreated rabbits. These animals also showed higher specific activities of two brush-border enzymes, sucrase and aminopeptidase N, than the control animals.

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.

The effect of Ca2+ antagonists on spontaneous motility from sheep duodenum.

Longitudinal smooth muscle of the sheep duodenum showed a rhythmic spontaneous activity with an average frequency of 5.6 +/- 0.55 phasic movements min-1 and a mean value of the amplitude of phasic contractions of 0.956 +/- 0.1 g. When the strips were incubated in Ca(2+)-free medium, the spontaneous motility amplitude (SMA) was reduced to 37 +/- 8.2% of control values. In Ca(2+)-free medium plus EDTA (1 or 2 mM), the SMA was strongly reduced to 21.9 +/- 8.3 and 1.8 +/- 1.8%, respectively. Verapamil, nifedipine and diltiazem diminished the SMA. The EC50 value for verapamil was 10(-9) M, whereas that for diltiazem was 2 x 10(-9) M and for nifedipine was 3 x 10(-14) M. Trifluoperazine and TMB-8 reduced the SMA with EC50 values of 7 x 10(-6) and 3 x 10(-5) M, respectively. The spontaneous activity in the sheep duodenum seemed to be mediated by influx extracellular Ca2+, which enters through potential-dependent channels and intracellular Ca2+ release.