Enteric viruses in New Zealand drinking-water sources.

This study determined whether human pathogenic viruses are present in two New Zealand surface waters that are used as drinking-water sources. Enteric viruses were concentrated using hollow-fibre ultrafiltration and detected using PCR for adenovirus (AdV), and reverse transcription PCR for norovirus (NOV) genogroups I-III, enterovirus, rotavirus (RoV) and hepatitis E virus (HEV). Target viruses were detected in 106/109 (97%) samples, with 67/109 (61%) samples positive for three or more viral types at any one time. AdV, NoV and ROV were detected the most frequently, and HEV the least frequently. Human NoV was not usually associated with animal NOV. Our results suggest that New Zealand would be well served by assessing the ability of drinking-water treatment plants to remove viruses from the source waters, and that this assessment could be based on the viral concentration of AdV-NoV-RoV. The long-term aim of our work is to use this information to estimate the risk of waterborne viral infection.

Antagonists of bombesin/gastrin releasing peptide based on [D-Ala24]GRP(20-26)-heptapeptide. Modifications leading to potent analogues with prolonged duration of action.

Analogues of gastrin releasing peptide (GRP) and bombesin based on His-Trp-Ala-Val-D-Ala-His-Leu, the 20-26 heptapeptide sequence of [D-Ala24]GRP, have been synthesized and tested in vitro for their ability to inhibit GRP (18-27)-induced mitogenesis in Swiss 3T3 cells. Compounds identified as potent antagonists in this test system were also tested in vivo for their ability to inhibit bombesin-induced amylase secretion in rats. The Trp-Ala-Val sequence was found to be a very important feature of the antagonist activity; most substitutions in this region led either to much less potent or inactive analogues. In contrast, amino acid replacements in other parts of the molecule were more tolerated and sometimes led to marked increases in the in vitro and in vivo activity. The most potent analogues were obtained by replacing Leu26 by MeLeu and His25 by Lys(X) where X = Z, PhCO, PhCH2CO or Ph(CH2)2CO. Thus 4-pyridylcarbonyl-His-Trp-Ala-Val-D-Ala-Lys(CO-CH2-CH2-Ph)-Leu- NHMe (86) and 4-pyridylcarbonyl-His-Trp-Ala-Val-D-Ala-Lys(Z)-MeLeu-OMe (87) had IC50 values of less than 20 micrograms/kg s.c. in vivo, and their effects lasted for more than 3 hr.

N-isobutyryl-His-Trp-Ala-Val-D-Ala-His-Leu-NHMe (ICI 216140) a potent in vivo antaconist analogue of bombesin/gastrin releasing peptide (BN/GRP) derived from the C-terminal sequence lacking the final methionine residue.

The GRP receptor mediated growth response in Swiss 3T3 cells has been used to identify BN/GRP antagonists. Analysis of bombesin antagonism by substance P analogues and by truncated GRP analogues revealed that deletion of the C-terminal methionine residue was important for antagonism. Des-Met analogues showing potent antagonist activity in the in vitro 3T3 system (IC50 approximately 2nM) were synthesized. Further structural modification of these peptides led to the identification of (CH3)2CHCO-His-Trp-Ala-Val-D-Ala-His-Leu-NHCH3 (ICI 216140) which reduced bombesin-stimulated rat pancreatic amylase secretion to basal levels when administered subcutaneously at 2.0 mg per kg.

The H+/ATP stoichiometry of the (H+ +K+)-ATPase of dog gastric microsomes.

Gastric microsomal vesicles isolated from dog fundic mucosa were shown to be relatively ion tight and have a low level of proton permeability. The H+ translocase, basal ATPase and K+-activated ATPase activities of these vesicles were measured and the H+/ATP stoichiometry calculated using either the total K+-ATPase or the K+-stimulatable component (total K+-ATPase--basal ATPase). The former estimations consistently gave stoichiometric of approximately one, whereas the use of only the K+-stimulatable component gave widely differing values. Measurement of the dephosphorylation of the enzyme under basal conditions revealed both a labile and a stable phosphoenzyme component. The rate of decay of the labile component completely accounted for the basal ATPase activity observed. We conclude that the basal ATPase associated with our preparations is a spontaneous dephosphorylation of the phosphoenzyme occurring in the absence of K+ and that the H+/ATP stoichiometry of the gastric ATPase is one.

The localization of a histamine H2-receptor adenylate cyclase system in canine parietal cells and its inhibition by prostaglandins.

A method is described for the preparation of parietal cell-enriched suspensions from dog gastric mucosa. Histamine and E type prostaglandins produce an elevation of cyclic AMP concentration in mixed cell preparations. Parietal cell-rich fractions respond to histamine but only weakly to prostaglandins whilst in fractions virtually free from parietal cells the converse is observed. Prostaglandins which are good antisecretory agents, PGE1, PGE2 and 16,16 dimethyl PGE2 are potent inhibitors of the histamine elevations of cyclic AMP in parietal cell-rich fractions, whilst PFG2alpha shows 1% of their potency. The experiments described support the view that histamine stimulates gastric acid secretion by excitation of an H2-receptor adenylate cyclase system in the plasma membrane of the parietal cell and that acid secretory inhibition by prostaglandins is a result of inhibition of that system.

Characterization of an adenylate cyclase system sensitive to histamine H2-receptor excitation in cells from dog gastric mucosa.

A method of preparing viable cells from dog gastric mucosa is described. Cyclic AMP in these cells is elevated by histamine and 4-methyl histamine but 2-methyl histamine is only a weak agonist. The effects on cyclic AMP levels are inhibited competitively by metiamide and burimamide which give apparent KBvalues of 3.5x10-7 M and 2.3x10-6 M, respectively. These values are similar to those reported for other histamine H2-receptor systems. The H1-receptor antagonists, mepyramine and chlorpheniramine, have no inhibitory effect on the histamine induced elevation of cyclic AMP: promethazine inhibits the system but not by a competitive mechanism. It is concluded that the histamine stimulated adenylate cyclase system is probably located in the parietal cell component.