Review of the implications of dietary tryptophan intake in patients with irritable bowel syndrome and psychiatric disorders.

In this review, we address the possible role of the essential amino acid L-tryptophan or its metabolic derivative 5-hydroxytryptophan in the modulation of serotonin (5-hydroxytryptamine) synthesis and thereby in affecting the pathophysiology of central and peripheral nervous system disorders, including depression and irritable bowel syndrome. L-Tryptophan may represent a link between apparently disparate functional disorders and is of interest for general gastroenterologists, neurogastroenterologists, and neurologists. On the basis of estimates showing that approximately 20% of patients with functional bowel disorders seeking care in referral centres have psychiatric comorbidity, we attempt to provide a conceptual framework for defining the possible role of L-tryptophan in this population.

5-HT4 receptors contribute to the motor stimulating effect of levosulpiride in the guinea-pig gastrointestinal tract.

BACKGROUND: The dopamine D2 receptor antagonist levosulpiride is a substituted benzamide derivative, whose gastrokinetic properties are exploited clinically for the management of functional dyspepsia. However, for other benzamide derivatives, such as cisapride and mosapride, agonism towards serotonin 5-HT4 receptors is considered the main mechanism leading to gastrointestinal prokinesia. AIMS: To assess whether levosulpiride is able to activate 5-HT4 receptors in the guinea-pig isolated gastrointestinal tract. MATERIALS AND METHODS: Circular muscle strips from gastric antrum, and colonic longitudinal muscle strips were used to detect electrically stimulated neurogenic contractions. The effect of levosulpiride was assessed in the absence and presence of GR125487, a selective 5-HT4 receptor antagonist. Furthermore, potential interaction of levosulpiride with 5-HT3 receptors and tissue cholinesterases was assessed in unstimulated ileal longitudinal muscle-myenteric plexus preparations. RESULTS: Antral and colonic strip contractions were cholinergic/tachykinergic in nature. Micromolar concentrations of levosulpiride potentiated submaximal responses, through a mechanism competitively antagonized by GR125487 (pKB=9.4). In LMMPs, levosulpiride slightly affected contractions caused by the 5-HT, receptor agonist 2-methyl-5-HT, and had no effect on contractions to exogenous acetylcholine. CONCLUSIONS: Our results indicate that levosulpiride acts as a moderate agonist at the 5-HT4 receptor. This property, together with antagonism at D2 receptors, may contribute to its gastrointestinal prokinetic effect.

Review article: cardiac adverse effects of gastrointestinal prokinetics.

Gastrointestinal prokinetics, such as metoclopramide, cisapride and levosulpiride, are widely used for the management of functional gut disorders. Recently, several studies have shown that cisapride (a partial 5-HT4 receptor agonist) can induce dose-dependent cardiac adverse effects, including lengthening of the electrocardiographic QT interval, syncopal episodes and ventricular dysrhythmias. Until recently, it was not clear whether these effects were dependent on 5-HT4 receptor activation or related to peculiar characteristics in the molecular structure of single agents within the benzamide class. Experimental evidence now favours the second hypothesis: cisapride possesses Class III antiarrhythmic properties and prolongs the action potential duration through blockade of distinct voltage-dependent K+ channels, thus delaying cardiac repolarization and prolonging the QT interval. Patients at risk of cardiac adverse effects are children, subjects with idiopathic, congenital or acquired long QT syndrome and, in particular, those receiving concomitant medication with Class III antiarrhythmic agents, some H1-receptor antagonists (e.g. terfenadine), or drugs such as azole antifungals (e.g. ketoconazole, itraconazole, miconazole and fluconazole) and macrolide antibacterials (e.g. erythromycin, clarithrod-mycin and troleandomycin), which can inhibit cisapride metabolism by interfering with the CYP3A4 isoenzyme.

Fluoroquinolone-induced motor changes in the guinea-pig isolated ileum.

The effects of norfloxacin and enoxacin were examined on spontaneous motor activity in the guinea-pig isolated ileum. Micromolar concentrations of both compounds caused a biphasic response consisting of relaxation followed by transient contraction. Relaxation to norfloxacin, which was unaffected by phentolamine, propranolol and hyoscine (each at 1 microM), was partially sensitive to tetrodotoxin (1 microM). This indicates that the response is partly mediated by non-adrenergic non-cholinergic (NANC) inhibitory nerves, and partly related to a direct action on the smooth muscle. Apamin (0.1 microM) and suramin (300 microM) inhibited norfloxacin-induced relaxations to an extent similar to that of tetrodotoxin. Conversely, NG-nitro-L-arginine (300 microM) was ineffective. In the presence of theophylline (100 microM) and 3-isobutyl-1-methylxanthine (10 microM), norfloxacin caused relaxation less effective than when added alone. Based on this observation, the NANC component of the relaxation apparently depends on ATP release, whereas the direct component might be due, at least in part, to phosphodiesterase inhibition. Norfloxacin-induced contractions were neurogenic and cholinergic in nature. They were reduced by indomethacin or S-ketoprofen (both at 0.01-1 microM) and suramin (300 microM), suggesting involvement of local prostaglandin production probably induced by ATP release. Previous findings revealed that norfloxacin acted as a non-competitive antagonist at enteric GABAA receptors. In this study the same property was shared by enoxacin against the contractile response to 3-aminopropane sulphonic acid (3-APS), a GABAA receptor agonist. In conclusion, fluoroquinolones exert inhibitory and excitatory effects in the guinea-pig ileum. These are mediated by ATP, prostaglandin and acetylcholine release that might underlie, at least in part, the alterations of gastrointestinal motility observed after fluoroquinolone administration. Furthermore, isolated intestinal preparations might be useful to predict the GABAA-antagonist potential of this class of compounds.

The effects of bone resorption inhibitors on the growth plate and proximal tibial metaphysis of rats: clinical implications.

This study investigated the effects of diphosphonates at scalar doses in a high bone turnover structure, namely, the proximal tibial metaphysis of rats. Arrest of bone modeling was represented by cylindrical-shaped metaphyses, increased height of the perichondrial bone bark, and persistence of primary metaphyseal trabeculae; these changes were dose-related. Higher doses of the inhibitors produced extension of the growth plate and arrest of the mineralization process. The dose-related dissociation between the effects on bone resorption and mineralization allows the therapeutic use of this class of drugs.

Endomorphin-1 and endomorphin-2 activate mu-opioid receptors in myenteric neurons of the guinea-pig small intestine.

The novel opioid tetrapeptides, endomorphin-1 and endomorphin-2, recently isolated from bovine and human brain bind with high affinity and selectivity to central mu-opioid receptors. In the digestive tract, a comprehensive pharmacological analysis of the receptors involved in endomorphin action has not been reported. In this study, we analyzed the effects of endomorphin-1 and endomorphin-2 on longitudinal muscle-myenteric plexus preparations (LMMPs) from the guinea-pig ileum. Both peptides (30 pM - 1 microM) inhibited (-log EC50 values: 8.61 and 8.59, respectively) the amplitude of electrically-induced twitch contractions in a concentration-dependent fashion, up to its abolition. Conversely, in unstimulated LMMPs, they failed to affect contractions to applied acetylcholine (100 nM). In stimulated LMMPs, the highly selective mu-opioid receptor antagonist, D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), caused a concentration-dependent (30 nM-1 microM), parallel rightward shift of endomorphin-1 and endomorphin-2 inhibitory curves, without depression of their maximum. Following Schild analysis, calculated pA2 values were 7.81 and 7.85, respectively, with slopes not different from unity. Concentration-response curves to both peptides were not affected by 30 nM naltrindole (a selective delta-receptor antagonist) or 30 nM nor-binaltorphimine (a selective kappa-receptor antagonist). These results demonstrate that endomorphins selectively activate mu-opioid receptors located on excitatory myenteric plexus neurons, and that they act as full agonists.

The effects of mechanical forces on bones and joints. Experimental study on the rat tail.

We have used an experimental model employing the bent tail of rats to investigate the effects of mechanical forces on bones and joints. Mechanical strain could be applied to the bones and joints of the tail without direct surgical exposure or the application of pins and wires. The intervertebral disc showed stretched annular lamellae on the convex side, while the annulus fibrosus on the concave side was pinched between the inner corners of the vertebral epiphysis. In young rats with an active growth plate, a transverse fissure appeared at the level of the hypertrophic cell layer or the primary metaphyseal trabecular zone. Metaphyseal and epiphyseal trabeculae on the compressed side were thicker and more dense than those of the distracted part of the vertebra. In growing animals, morphometric analysis of hemiepiphyseal and hemimetaphyseal areas, and the corresponding trabecular bone density, showed significant differences between the compressed and distracted sides. No differences were observed in adult rats. We found no significant differences in osteoclast number between compressed and distracted sides in either age group. Our results provide quantitative evidence of the working of 'Wolff's law'. The differences in trabecular density are examples of remodelling by osteoclasts and osteoblasts; our finding of no significant difference in osteoclast numbers between the hemiepiphyses in the experimental and control groups suggests that the response of living bone to altered strain is mediated by osteoblasts.

Endothelin and nitric oxide synthase in lymphatic endothelial cells: immunolocalization in vivo and in vitro.

BACKGROUND: Endothelin (ET) is an endothelium-derived multifunctional peptide that produces a potent, long-lasting vasoconstriction. Nitric oxide (NO), besides being the most important endothelium-derived relaxant factor in blood vessels, is supposed to be involved in regulating the interactions among endothelium, adhesive molecules, and leukocytes. METHODS: We investigated the possible occurrence and distribution of ET and constitutive nitric oxide synthase (NOs), the enzyme that generates NO from L-arginine, in bovine lymphatic vessels and primary culture of lymphatic endothelium by using immunocytochemistry. RESULTS: Specific immunostaining with both ET and endothelial constitutive NOs antisera was detectable at light and electron microscopic levels in the endothelial cell layer of lymphatic vessels, whereas no immunostaining could be observed in the muscular and adventitial layers. The immunoreaction showed a diffuse pattern throughout the cytoplasm of endothelial cells. Primary cultures of endothelial cells isolated from lymphatic vessels also displayed cytoplasmic ET- and NOs-like immunoreactivities. The endothelial nature of cell monolayers was confirmed by the positive reaction to the von Willebrand factor, a reliable marker of endothelial cells, and by ultrastructural features of cultured cells. CONCLUSIONS: These findings suggest that the endothelium is a major source of ET and NO in lymphatic vessels. Interestingly, the lymphatic endothelium maintains the capability of producing such vasoactive sustances also in vitro, thus suggesting that lymphatic endothelial cells in culture may be used in studies concerning the role of the endothelium in the generation of vasoactive molecules. According to previous functional studies, the occurrence of ET and NOs immunoreactivities in lymphatic vessel endothelium supports the view that lymphatic endothelium may play an important role in the regulation of lymphatic vascular tone and in the production of vascular contractile activity promoting lymph flow.

Quantitative evaluation of the bone-metal interface in implants with two different surface roughnesses: an experimental study in rabbits.

Direct bone-metal contact is considered the ideal condition in order to obtain stability of orthopaedic non cemented implants. To acheive this result various implant shapes and surfaces were proposed.

The reaction to nailing or cementing of the femur in rats. A microangiographic and fluorescence study.

Bone reaction to cement and to a cementless stem was studied in the rat femur with histological fluorescence and microangiographic techniques. Periosteal and endosteal apposition, and consequent remodelling, appeared as a reaction to reaming rather than caused by cement or a cementless stem. Every change in bone began with proliferation, progression and orientation of the vessels. Endosteal apposition was absent in cemented femurs because the entire medulla was occupied by the acrylic cement, but remodelling of the subendosteal cortex followed medullary revascularisation which was far advanced after 90 days. In cementless stems, endosteal apposition of primary woven bone and remodelling was the basis for bony ingrowth and anchorage through bony bridges. Our results suggest that the pattern of blood supply is relevant to the structural organisation of mature lamellar bone around the implant. Cemented stems have maximum anchorage and stability as soon as they are inserted, but this decreases with time as revascularisation occurs. Cementless stems can reach maximum integration later after insertion, and revascularisation is less critical because they usually do not fill the canal completely.

A re-appraisal of the nature of the atropine-resistant contraction to electrical field stimulation in the human isolated detrusor muscle.

We investigated whether in human isolated detrusor strips the atropine-resistant contractile response to electrical field stimulation was mediated by ATP (or a related purine), as previously shown in the urinary bladder of other mammalian species. Electrical stimulation (1-50 Hz for 5 s at 1 min intervals, 0.1 ms pulse width, 60 V) elicited reproducible, frequency-dependent twitch contractions, which were markedly reduced by atropine (10 microM). Tetrodotoxin (TTX: 1 microM) inhibited contractile responses to a similar degree. When applied together, atropine and TTX caused an inhibition which was superimposable to that caused by either drug alone. The TTX-resistant contractions were totally unaffected by omega-conotoxin GVIA (omega-CTX: 0.1 microM). The atropine-resistant contractions were unaffected by the P2-purinoceptor antagonists suramin (300 microM) and PPADS (30 microM), at concentrations which virtually suppressed the contractile response induced by applied ATP (10 microM(-1) mM). As previously described, antagonism of the ATP-induced contractions by suramin (30, 100, 300 microM) and PPADS (3, 10, 30 microM) was insurmountable, with apparent 'pA2' values (calculated at the lowest antagonist concentrations) of 4.9 and 5.2, respectively. It is concluded that, under our experimental conditions, the non-cholinergic (atropine-resistant) component of the excitatory transmission in the human detrusor is not mediated by neural release of ATP, in spite of the presence of excitatory P2-purinoceptors on the effector cells. The TTX- and omega-CTX-resistant, non-cholinergic component might be related to the release of unknown transmitter(s) through a mechanism independent of both Na+- and N-type Ca2+-channels. More likely, the atropine-resistant component may reflect direct smooth muscle excitation since the human detrusor has a very short chronaxie (Sibley 1984).

P-selectin and von Willebrand factor in bovine mesenteric lymphatics: an immunofluorescent study.

P-selectin (PADGEM, GMP-140, CD62) is an integral membrane protein specific to alpha granules of platelets and Weibel-Palade bodies of blood vascular endothelial cells. The presence in lymphatic endothelial cells of numerous Weibel-Palade bodies and their positivity to immunocytochemical reaction for von Willebrand factor have previously been characterized and described. Because von Willebrand factor and P-selectin codistribute in Weibel-Palade bodies of blood vascular endothelial cells we investigated the presence of both P-selectin and von Willebrand factor in lymphatic endothelium. Lymphatic vessels expressed positive reaction to immunocytochemical assay thereby demonstrating the presence of P-selectin in the endothelium. Distribution and intensity of the reaction were similar to those observed in bovine blood vascular endothelium.

Effects of ethanol administration on cerebral non-protein sulfhydryl content in rats exposed to styrene vapour.

Glutathione (GSH) and other non-protein sulfhydryls (NPS) are known to protect cells from oxidative stress and from potentially toxic electrophiles formed by biotransformation of xenobiotics. This study examined the effect of a simultaneous administration of styrene and ethanol on NPS content and lipid peroxidation in rat liver and brain. Hepatic cytochrome P450 and cytochrome b5 content, aniline hydroxylase and aminopyrine N-demethylase activities as well as the two major urinary metabolites of styrene, mandelic and phenylglyoxylic acids were also measured. Groups of rats given ethanol for 3 weeks in a liquid diet were exposed, starting from the second week, to 326 ppm of styrene (6 h daily, 5 days a week, for 2 weeks). In control pair-fed animals, styrene produced about 30% depletion of brain NPS and 50% depletion of hepatic NPS. Subchronic ethanol treatment did not affect hepatic NPS levels, but caused 23% depletion of brain NPS. Concomitant administration of ethanol and styrene caused a NPS depletion in brain tissue in the order of 60%. These results suggest that in the rat, simultaneous exposure to ethanol and styrene may lead to considerable depletion of brain NPS. This effect is seen when both compounds are given on a subchronic basis, a situation which better resembles possible human exposure.

Reversibility of the inhibitory effect of salmon calcitonin on bone resorption in rats.

Inhibition of osteoclastic bone resorption has been induced in growing rats with high doses of salmon calcitonin. This effect was evaluated by measuring the perichondrial ring height of the proximal tibial metaphysis. The aim was to assess whether osteoclastic activity resumed after a period of inhibition with high doses of calcitonin. 20 male Sprague-Dawley rats were treated for 21 days with 100 units/kg/day of salmon calcitonin subcutaneously and killed after 0-60 days, together with non-treated controls at 0 and 60 days. Arrest of metaphyseal modeling and increased height of the perichondrial ring at the end of the period of therapy (P 0.002 versus controls) were observed. Recovery of bone resorption was evident 20 and 40 days after withdrawal of calcitonin.

Histology of the metal-bone interface: interpretation of plastic embedded slides.

The interference of processing and preparation of histological slides for the study of morphology and morphometry of bone-implant interfaces was investigated in an experimental model, in which a titanium plate was inserted through the cortical bone into the medullary cavity of rat tibiae. The thickness of the sections, burr and notching of the cut border, and staining properties of the embedding resin were found to significantly influence the appearance of the bone-implant interface and, when morphometry was applied, the extent of direct bone-metal contact. The model of the interface resulting from this study is that of some bony processes abutting on the metal surface, while most of the contact is between metal and connective tissue or vascular spaces.

Experimental model in vivo for quantitative assessment of bone resorption inhibition.

Quantitative assessment of bone resorption inhibition in vivo is not easily accomplished; methods relying on a count of osteoclasts are questionable, and histomorphometric evaluation of the bone mass presents several technical problems as well. The authors developed a simple method to measure the inhibition of bone resorption by study of the proximal tibial metaphysis of growing rats: the height of the perichondrial bone ring was taken as an index of the balance between osteoblastic and osteoclastic activity because any agent that inhibits osteoclasts (without interference with osteoblasts) produces an increase in the height of this anatomical structure. Since the ring is well demarcated by surrounding tissues, its height can be measured with accuracy and used for quantitative assessment of bone resorption inhibition. This model was tested with salmon calcitonin, and it provides evidence in vivo that this hormone inhibits osteoclastic bone resorption.

Inhibitory effect of salmon calcitonin on bone resorption: morphological study of the tibial growth plate in rats.

Salmon calcitonin (sCT) at doses of 100 and 50 UI given subcutaneously to growing rats produced in vivo evidence of osteoclastic activity inhibition. Histological assessment was carried out by measuring the perichondrial ring of Lacroix height, and a dose-correlated effect was found. These aspects were coupled with an increase in the osteoclast number and suggested that in studies with bone resorption inhibitors, morphological evaluation based on osteoclasts count is not reliable. The changes of the metaphysis suggested also that sCT affects the activity of hypertrophic chondrocytes of the growth plate. Plasma calcium levels did not differ significantly between treated rats and controls; an increased phosphatemia was observed in sCT-treated animals.

Effects of thallium on primary cultures of testicular cells.

The objective of this in vitro study was to examine the response of mixed cultures of Sertoli and germ cells to treatment with thallium (Tl) at the range of concentrations that, in previous studies, was shown in vivo to affect reproduction. Cultures were prepared from the testis of Sprague-Dawley rats. Cultures containing approximately 3.75 x 10(6) cells/ml were treated with Tl concentrations corresponding to 35, 7, and 1.4 micrograms Tl/g testis, estimated from protein content of cultures. Observations at 24, 48, and 72 h after treatment showed a significant release of germ cells into the culture medium that was both concentration and time dependent. Cultures treated with 35 micrograms Tl/g testis showed a threefold increase in germ-cell detachment compared with controls after only 24 h of exposure. As the treatment time increased to 48 h of exposure, even cultures exposed at the lowest Tl concentration (1.4 micrograms Tl/g testis) showed significant loss of germ cells. After 48 h, cultures exposed to 7 micrograms Tl/g testis exhibited a 2.5-fold increase in germ-cell detachment, and those exposed to 35 micrograms Tl/g testis exhibited a 10-fold increase over controls. Morphological investigations of cell cultures showed evident loss of germ cells with significant reduction in prepachytene and pachytene spermatocytes and changes in the shape of Sertoli cells. These results are in agreement with in vivo studies, in which thallium treatment at comparable exposure levels manifested its earliest toxic testicular effects in Sertoli and germ cells. They also demonstrate the usefulness of this in vitro culture technique to assess toxic testicular damage rapidly.

Biliary excretion of barium in the rat.

Biliary excretion of barium was studied in Sprague-Dawley bile-duct-cannulated rats injected intravenously with 1.8 micrograms Ba/rat as 133Ba-labeled barium chloride. Approximately 0.5% of the barium dose was excreted into bile within 2 h. The time-course profile of biliary excretion of the radiotracer closely reflected that of plasma concentrations. Biliary barium levels reached their peak in the first 15-min period after administration and rapidly declined thereafter. The plasma-to-bile barium-concentration ratio was approx 1 at 2 h after injection. There was no tendency of barium to concentrate in liver, and the 133Ba levels in stomach and small intestine largely exceeded hepatic levels. There is evidence indicating that barium is predominantly excreted with feces following parenteral administration in rats and humans. The results of this study suggest that biliary excretion is of little quantitative importance and that physiological routes other than bile contribute to elimination of barium by the digestive tract.