NPR-C receptors are involved in C-type natriuretic peptide response on bile secretion

C-type natriuretic peptide (CNP) is a member of the natriuretic peptide family. Previous studies reported the presence of natriuretic peptide receptors and mRNA CNP in the liver. In the present work, we sought to establish the role of CNP in the regulation of bile secretion in the rat and the possible pathways involved.CNP diminished basal as well as bile salt-evoked bile flow and bile acid output in a dose-dependent manner. It also reduced the excretion of sodium, chloride, and potassium but did not modify bile pH or the excretion of phospholipids, total proteins, and glutathione. Neither parasympathetic nor sympathetic blockade abolished CNP inhibitory response on bile secretion. The selective NPR-C agonist, C-ANP-(4-23) amide, diminished bile flow and the co-administration of both peptides did not further decrease it. CNP did not alter mean arterial pressure or portal venous pressure at any given doses.CNP decreased bile acid-dependent flow without affecting bile acid-independent flow. The inhibitory effect of CNP did not involve the participation of the autonomic nervous system or hemodynamic changes. The participation of NPR-C receptors in CNP response is strongly supported by present findings. The present study shows that CNP modulates bile secretion in the rat, suggesting that CNP may be part of the large family of peptides involved in the regulation of gastrointestinal physiology.     

Sub-chronic toxicity and test of eye irritability of leaf aqueous extract from Plantago major (plantaginaceae)

For the sub-chronic toxicity an aqueous preparation of Plantago major leaves was tested in 20 male NGP mice, with an average weight of 20.15 g and separated in two groups of ten individuals each. The dose used was 2000 mg/kg and the control group received 0.5 ml of distilled water. The extract administration was done daily during five days at week for a total period of 40 days. Signs of sub-chronic toxicity were observed in the days two and 12 of treatment. No significant change in corporal weight was observed. The ocular irritation was tested in five New Zeland male rabbits, with an average weight of 3.640 kg. The dose used was a 200 microliters the preparation (100 mg/ml) of Plantago major leaves, instill into the right eye and the control was used the left eye instill 200 microliters of distilled water. The administration was done daily during five days. The extract shows no significant irritation during the observation period.     

Atrial natriuretic factor stimulates exocrine pancreatic secretion in the rat through NPR-C receptors

Increasing evidence supports the role of atrial natriuretic factor (ANF) in the modulation of gastrointestinal physiology. The effect of ANF on exocrine pancreatic secretion and the possible receptors and pathways involved were studied in vivo. Anesthetized rats were prepared with pancreatic duct cannulation, pyloric ligation, and bile diversion into the duodenum. ANF dose-dependently increased pancreatic secretion of fluid and proteins and enhanced secretin and CCK-evoked response. ANF decreased chloride secretion and increased the pH of the pancreatic juice. Neither cholinergic nor adrenergic blockade affected ANF-stimulated pancreatic secretion. Furthermore, ANF response was not mediated by the release of nitric oxide. ANF-evoked protein secretion was not inhibited by truncal vagotomy, atropine, or Nomega-nitro-l-arginine methyl ester administration. The selective natriuretic peptide receptor-C (NPR-C) receptor agonist cANP-(4-23) mimicked ANF response in a dose-dependent fashion. When the intracellular signaling coupled to NPR-C receptors was investigated in isolated pancreatic acini, results showed that ANF did not modify basal or forskolin-evoked cAMP formation, but it dose-dependently enhanced phosphoinositide hydrolysis, which was blocked by the selective PLC inhibitor U-73122. ANF stimulated exocrine pancreatic secretion in the rat, and its effect was not mediated by nitric oxide or parasympathetic or sympathetic activity. Furthermore, CCK and secretin appear not to be involved in ANF response. Present findings support that ANF exerts a stimulatory effect on pancreatic exocrine secretion mediated by NPR-C receptors coupled to the phosphoinositide pathway.     

Dexamethasone prevents virus-induced hyperresponsiveness via multiple mechanisms

In the lungs, neuronal M2 muscarinic receptors inhibit acetylcholine release from the parasympathetic nerves. Parainfluenza virus infection causes loss of M2 receptor function, which increases acetylcholine release and vagally mediated bronchoconstriction. Because glucocorticoids are known to inhibit airway hyperresponsiveness, we tested whether dexamethasone (6.5 or 65 microg/kg i.p.) prevents virus-induced hyperresponsiveness and M2 receptor dysfunction in guinea pigs. In controls, pilocarpine, a muscarinic agonist, inhibited vagally induced bronchoconstriction, demonstrating functional M2 receptors. However, in virus-infected animals, pilocarpine failed to inhibit vagally induced bronchoconstriction, demonstrating M2 receptor dysfunction. Frequency-dependent bronchoconstriction was greater in virus-infected animals than in controls, indicating airway hyperresponsiveness. Low-dose dexamethasone (6.5 microg/kg i.p.) treatment prevented virus-induced airway hyperresponsiveness, ameliorated M2 receptor dysfunction, and decreased viral content in the lungs without inhibiting virus induced inflammation. High-dose dexamethasone (65 microg/kg i.p.) prevented virus-induced hyperresponsiveness, completely reversed M2 receptor dysfunction, decreased viral titers, and decreased virus-induced inflammation. This high-dose dexamethasone also increased M2 receptor function in uninfected animals. In conclusion, dexamethasone prevented virus-induced hyperresponsiveness and M2 receptor dysfunction via multiple mechanisms.     

Silymarin increases antioxidant enzymes in alloxan-induced diabetes in rat pancreas

The aim of this study was to analyze the effect of the flavonoid silymarin, a free radical scavenger that prevents lipoperoxidation, on the pancreatic activity of superoxide dismutase (SOD), glutathione peroxidase (GSHPx) and catalase (CAT) in rats with alloxan-induced diabetes mellitus. Alloxan intoxicated rats were treated with silymarin in two manners, simultaneously (four or eight doses) or 20 days after alloxan administration for 9 weeks. Alloxan elicited a transient increase in the activity of the three enzymes, which decreased after 5 days of treatment. On its own, silymarin significantly increased the activity of these enzymes. Simultaneous treatment with alloxan and silymarin also induced an increment in the activity of the enzymes followed by a delayed decrease (four doses). However, a longer treatment with silymarin (eight doses) induced a more sustained effect. Interestingly, silymarin treatment recovered to control values for the activity of the three-antioxidant enzymes that were significantly diminished after 20 days of alloxan administration. It is suggested that the protective effect of silymarin on pancreatic damage induced by alloxan may be due to an increase in the activity of antioxidant enzymes that, in addition to the glutathione system, constitute the more important defense mechanisms against damage by free radicals.     

Targeted suppression of the ferroxidase and iron trafficking activities of the multicopper oxidase Fet3p from<Emphasis Type="Italic"> Saccharomyces cerevisiae</Emphasis>

The Fet3 protein in Saccharomyces cerevisiae is a multicopper oxidase tethered to the outer surface of the yeast plasma membrane. Fet3p catalyzes the oxidation of Fe(2+) to Fe(3+); this ferroxidation reaction is an obligatory first step in high-affinity iron uptake through the permease Ftr1p. Here, kinetic analyses of several Fet3p mutants identify residues that contribute to the specificity that Fet3p has for Fe(2+), one of which is essential also to the coupling of the ferroxidase and uptake processes. The spectral and kinetic properties of the D278A, E185D and A, Y354F and A, and E185A/Y354A mutants of a soluble form of Fet3p showed that all of the mutants exhibited the normal absorbance at 330 nm and 608 nm due to the type 3 and type 1 copper sites in Fet3p, respectively. The EPR spectra of the mutants were also equivalent to wild-type, showing that the type 1 and type 2 Cu(II) sites in the proteins were not perturbed. The only marked kinetic defects measured in vitro were increases in K(M) for Fe(2+) exhibited by the D278A, E185A, Y354A, and E185A/Y354A mutants. These results suggest that these three residues contribute to the ferroxidase specificity site in Fet3p. In vivo analysis of these mutant proteins in their membrane-bound form showed that only E185 mutants exhibited kinetic defects in (59)Fe uptake. For the Fet3p(E185D) mutant, K(M) for iron was 300-fold greater than the wild-type K(M), while Fet3p(E185A) was completely inactive in support of iron uptake. In situ fluorescence demonstrated that all of the mutant Fet3 proteins, in complex with an Ftr1p:YFP fusion protein, were trafficked normally to the plasma membrane. These results suggest that E185 contributes to Fe(2+ )binding to Fet3p and to the subsequent trafficking of the Fe(3+) produced to Ftr1p.