Glucose-dependent insulinotropic polypeptide receptor (GIPR), a member of family B of the G-protein coupled receptors, is a potential therapeutic target for which discovery of nonpeptide ligands is highly desirable. Structure-activity relationship studies indicated that the N-terminal part of glucose-dependent insulinotropic polypeptide (GIP) is crucial for biological activity. Here, we aimed at identification of residues in the GIPR involved in functional interaction with N-terminal moiety of GIP. A homology model of the transmembrane core of GIPR was constructed, whereas a three-dimensional model of the complex formed between GIP and the N-terminal extracellular domain of GIPR was taken from the crystal structure. The latter complex was docked to the transmembrane domains of GIPR, allowing in silico identification of putative residues of the agonist binding/activation site. All mutants were expressed at the surface of human embryonic kidney 293 cells as indicated by flow cytometry and confocal microscopy analysis of fluorescent GIP binding. Mutation of residues Arg183, Arg190, Arg300, and Phe357 caused shifts of 76-, 71-, 42-, and 16-fold in the potency to induce cAMP formation, respectively. Further characterization of these mutants, including tests with alanine-substituted GIP analogs, were in agreement with interaction of Glu3 in GIP with Arg183 in GIPR. Furthermore, they strongly supported a binding mode of GIP to GIPR in which the N-terminal moiety of GIP was sited within transmembrane helices (TMH) 2, 3, 5, and 6 with biologically crucial Tyr1 interacting with Gln224 (TMH3), Arg300 (TMH5), and Phe357 (TMH6). These data represent an important step toward understanding activation of GIPR by GIP, which should facilitate the rational design of therapeutic agents.Glucose-dependent insulinotropic polypeptide (GIP; also known as gastric inhibitory polypeptide) is a 42-residue hormone released by the enteroendocrine K cells lining the proximal duodenum (Jörnvall et al., 1981;Moody et al., 1984). GIP stimulates insulin secretion from pancreatic ␤-cells after ingestion of nutrients. The peptide has a very short half-life in the blood because it is vulnerable to degradation by the ubiquitous enzyme dipeptidyl peptidase IV (Mentlein et al., 1993). GIP, along with its sister incretin hormone glucagonlike peptide 1, has been shown to account for 50 to 70% of postprandial insulin secretion. The incretin effect is strictly glucose-dependent and is essential for the maintenance of glucose homeostasis. GIP further enhances its glucose-lowering effects by the inhibition of hepatic glucose production and the stimulation of proinsulin gene transcription and translation. Because of its hypoglycemic and hypolipidemic effects (Brown, 1974;Baggio and Drucker, 2007), GIP and its receptor (GIPR) are of high pharmacological interest, especially in identification and design of new molecules for the treatment of diabetes mellitus and obesity (Kieffer, 2003). The expression of GIPR in different organs and systems such as stoma...

This study was intended to explore the oxidative status of broilers under cyclic heat stress (HS) as modulated by supplementation of mannan-oligosaccharides (MOS) and a probiotic mixture (PM). Two hundred fifty 1-d-old chicks were randomly divided into 5 groups. From d 22, birds were either kept in a thermoneutral zone (TN; 26.7°C for 24 h/d) or subjected to HS (35 ± 1.1°C and 75 ± 5% RH for 8 h/d from 1000 to 1800 h) to the conclusion of the study on d 42. Birds were fed either a corn-based diet (TN and HS groups) or the same diet supplemented with 0.5% MOS (HS-MOS group), 0.1% PM (HS-PM group), or their combination as a symbiotic (SYN; HS-SYN group). On d 42, birds were killed by cervical dislocation to collect serum for the determination of total oxidants, total antioxidants, paraoxonase, arylesterase, ceruloplasmin, aspartate aminotransferase, alanine aminotransferase, and trace minerals. Heat stress increased (P < 0.05) total oxidants and total antioxidants and decreased (P < 0.05) paraoxonase and arylesterase, with no change in ceruloplasmin, aspartate aminotransferase, and alanine aminotransferase activities. Dietary supplementation decreased (P < 0.05) total oxidants and total antioxidants, with no effect on the activities of other enzymes. Heat stress did not influence serum copper, zinc, and manganese concentrations of birds when compared with those in the TN group. However, MOS increased (P < 0.05) concentrations of all the trace minerals, whereas SYN increased (P < 0.05) concentrations of only zinc and copper. It was concluded that MOS or PM supplementation, alone or as a SYN, may reduce some of the detrimental effects of HS, whereas MOS alone or as a SYN may improve the absorption of trace minerals.

Authors' Contribution AK performed experiments. MT planned and supervised the study and provided guidance for manuscript write-up. ASH and TY facilitated the conduction of experiments. ARA and MW helped in data analysis. SS, SF and ARS helped in manuscript write-up.

The crude ethanolic extract of Chrozophora prostrata (Cp.Cr) was tested using in vivo and ex vivo assays for its possible bronchodilatory effects in order to validate its medicinal use in respiratory disorders, like asthma and cough. Cp.Cr exhibited dose-dependent inhibition of carbachol (CCh)-induced bronchospasm in anesthetized rats, similar to aminophylline. When tested on guinea-pig tracheal preparations, Cp.Cr caused relaxation of both CCh (1 μM) and high K(+) (80 mM)-induced contractions with comparable potencies, similar to papaverine, a dual inhibitor of phosphodiesterse (PDE) and Ca(+2) influx. Pre-treatment of the tracheal tissues with Cp.Cr resulted in potentiation of the inhibitory effect of isoprenaline on CCh-induced contractions, like that caused by papaverine indicative of PDE inhibitory activity, which was confirmed when Cp.Cr concentration dependently (1 and 3 mg/mL) increased intracellular cAMP levels of the tracheal preparations, like papaverine. Cp.Cr shifted concentrationresponse curves of Ca(+2) constructed in guinea-pig tracheal preparation towards right with suppression of the maximum response, similar to both verapamil and papaverine. These data indicate bronchodilator activity of Chrozophora prostrata mediated possibly through dual inhibition of PDE and Ca(+2) influx, thus, showing therapeutic potential in asthma with effect enhancing and side-effect neutralizing potential Copyright © 2016 John Wiley & Sons, Ltd.