A. Di Nucci

Effects of silver in isolated rat hepatocytes

Addition of silver nitrate or silver lactate to freshly isolated hepatocytes caused dose-dependent loss of cell viability, measured by trypan blue exclusion, at concentrations within 30-70 microM. Silver cytotoxicity was accompanied by a decrease in hepatic thiol concentration and an increase in lipid peroxidation. Treatment of hepatocytes with the reduced glutathione (GSH)-depleting agent diethylmaleate markedly increased their vulnerability to silver toxicity whereas protective effects were produced by the thiol-reducing agent, dithiothreitol. Both alpha-tocopherol, which protected from the onset of silver-associated lipid peroxidation, and the iron chelator agent, deferoxamine failed to prevent loss of cell viability. These data suggest that perturbation of intracellular thiol homeostasis may play a critical role in the mechanism underlying silver-induced lethal damage to isolated rat hepatocytes.

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

Abstract 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 (1–50Hz for 5s at 1min intervals, 0.1ms pulse width, 60V) elicited reproducible, frequency-dependent twitch contractions, which were markedly reduced by atropine (10μM). Tetrodotoxin (TTX: 1μM) 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 (ω-CTX: 0.1μM). The atropine-resistant contractions were unaffected by the P2-purinoceptor antagonists suramin (300μM) and PPADS (30μM), at concentrations which virtually suppressed the contractile response induced by applied ATP (10μM–1mM). As previously described, antagonism of the ATP-induced contractions by suramin (30, 100, 300μM) and PPADS (3, 10, 30μM) 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 ω-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).

Endomorphin-1 and endomorphin-2 activate µ-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 µ-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 µM) 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 µ-opioid receptor antagonist, d-Phe-Cys-Tyr-d-Trp-Orn-Thr-Pen-Thr-NH2 (CTOP), caused a concentration-dependent (30 nM–1 µM), 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 δ-receptor antagonist) or 30 nM nor-binaltorphimine (a selective κ-receptor antagonist). These results demonstrate that endomorphins selectively activate µ-opioid receptors located on excitatory myenteric plexus neurons, and that they act as full agonists.

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.

Thallium-induced testicular toxicity in the rat

Reproductive tract functions were studied in adult male Wistar rats given 10 ppm thallium as thallium sulfate in the drinking water. After 60 days of treatment, spermatozoa isolated from the cauda epididymides and vas deferens showed reduced motility and immature germ cells were found in the tubular lumen. Histological examination of testes in thallium-treated animals revealed disarrangement of the tubular epithelium and ultrastructural changes in the Sertoli cells with cytoplasmic vacuolation and distension of the smooth endoplasmic reticulum. The activity of testicular beta-glucuronidase was significantly reduced whereas acid phosphatase and sorbitol dehydrogenase activities were unchanged. Plasma testosterone levels were within normal limits. No abnormalities in testicular morphology and biochemistry were seen in animals sacrificed at the end of the first month of thallium exposure. These findings indicate that the male reproductive system is a susceptible target site to toxic effects of thallium under chronic exposure. They also suggest a major involvement of Sertoli cells in the mechanism underlying thallium-induced testicular damage.

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

Summary. 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.Résumé. A l’aide des techniques histologiques microangiographiques et à fluorescence, la réaction osseuse lors de l’introduction endomédullaire dans le fémur d’un rat de ciment acrylique et de tiges non cimentèes a étéétudiée. La réaction osseuse du périoste interne et externe et la reproduction osseuse ou le remodelage osseux paraissent être des phénomènes dûs au procedé de fraisage du canal médullaire plutot qu’à la réaction spécifique de la cimentation ou à l’introduction d’une tigue non cimentée. Tout changement de l’os, aussi bien en apposition qu’en remodelage implique une prolifération, une progression et une nouvelle orientation des vaisseaux. L’apposition du périoste interne n’apparait pas pour les fémurs cimentés et on observe un remodelage de l’endoste dû au phénomène de revascularisation médullaire; ce phénomène est trés evident aprés 90 jours. Pour les tiges non cimentées, par contre, l’apposition du perioste interne de la matrice osseuse primaire et le successif remodelage permettent la repousse osseuse sur la surface de l’implant, en le soudant à l’aide de ponts osseux à la superficie du périoste interne. Nous pouvons donc dire que d’aprés nos études, les tiges cimentées garantissent un ancrage optimal dés son application mais il est évident qu’au cours du temps, à cause du phénomène de revascularisation l’ancrage diminue. Les tiges non cimentées atteignent le maximum d’ancrage longtemps aprés l’implantation et le procedé de revascularisation est beaucoup moins critique vu que l’implant, habituellement ne remplit pas complétement le canal médullaire.

Effects of Phenobarbitone on the Distribution, Metabolism and Biliary Excretion of Erythromycin in Rats

The administration of phenobarbitone to the rat (8 mg/100 g BW) once daily for 3 days significantly decreased the serum and tissue levels of erythromycin administered intraperitoneally (5 mg/100 g BW). Furthermore, phenobarbitone stimulated the hepatic microsomal N-demethylation of erythromycin and increased the biliary concentration and the biliary excretion rate of the unmetabolized antibiotic. These effects were accompanied by augmented liver mass and bile flow. The possibility is discussed that erythromycin concentrates in the bile through a specialized hepatic drug transport system, activated by phenobarbitone.

Biliary Excretion of Barium in the Rat

Biliary excretion of barium was studied in Sprague-Dawley bileduct-cannulated rats injected intravenously with 1.8 μg Ba/rat as133Ba-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 the133Ba 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.

1,2-Dichloropropane-Induced Liver Toxicity: Clinical Data and Preliminary Studies in Rats

1,2-Dichloropropane (DCP) is an industrial solvent widely used as a component of household dry-cleaning products, in the paint industry, and in agriculture as a soil fumigant. In recent years, intoxications and fatalities have been described as the result of abuse (“sniffing”) and accidental or deliberate ingestion of commercial household products containing varying concentrations of DCP (Pozzi et al. 1985). Clinical features of poisoning by DCP-containing products have included blood disorders, renal failure, and hepatic damage (Ghezzi Laurenzi et al. 1987).