Protection of dogs from bites of phlebotomine sandflies by deltamethrin collars for control of canine leishmaniasis.

Dog collars made of PVC plastic impregnated with the pyrethroid insecticide deltamethrin at 40 mg/g were investigated for their protective efficacy against phlebotomine sandflies. Collared dogs were kept separately (two untreated control dogs lived together) in outdoor enclosures, each with a kennel, in the Cévennes, southern France. To measure sandfly mortality and anti-feeding effects due to the deltamethrin-impregnated collars worn continuously by the dogs for up to 8 months, each dog was periodically sedated and exposed for 2h to 150-200 laboratory-reared Phlebotomus perniciosus females (plus c. 25 males) inside a net (1.2 m square, 1.8 m high) indoors. After dogs were removed from the nets, allowed to recover and returned to their kennels, any dead sandflies were collected from inside the net and counted. Surviving flies were kept overnight, then scored according to whether they were still alive or dead, unfed or blood-fed. From tests 2, 3, 4, 13, 20, 26 and 34 weeks after the dogs began wearing collars, the overall numbers of blood-fed female sandflies recaptured were 75 from two dogs with collars, compared with 1911 from two collarless dogs. Thus, for every 100 flies which fed on collarless dogs, only 4 fed on collared dogs, i.e. the collars protected dogs from 96% of the bites and this activity was maintained for up to 34 weeks. During the same period, the percentage of recaptured female sandflies that had fed on collared dogs was 0-12% compared to 55-95% on collarless dogs. Immediately after dogs were taken out of the nets, 21-60% of flies confined with the collared dogs were found dead, compared to 0-12% with the controls. It is concluded that, at least in the Mediterranean subregion, this insecticidal collar would protect a dog from the majority of sandfly bites and retain a killing effect for a complete sandfly season. Moreover, it seems likely that the use of collars on all dogs in a focus of Leishmania infantum would reduce contact between sandfly vectors and canine reservoir hosts sufficiently to diminish the risk of infection for humans as well as dogs.

Inhibition of gastric acid secretion by oxyntomodulin and its 19-37 fragment in the conscious rat.

Oxyntomodulin (Oxm) is a hormone, released from the intestine during digestion. Its target tissue is the gastric mucosa, where it inhibits acid secretion. It contains the 29-amino acid glucagon moiety, extended at its COOH-terminal end by an octapeptide. The glucagon moiety contains a basic doublet (Arg17-Arg18). Our working hypothesis was that the mode of action of Oxm may imply a processing of the molecule at the Arg-Arg doublet, releasing Oxm-(19-37). We compared the effect of Oxm with that of Oxm-(19-37) on gastric acid secretion in the conscious rat provided with a chronic gastric fistula. The acid secretion was plateau stimulated by a perfusion of either pentagastrin or histamine. Whereas Oxm or Oxm-(19-37) had no effect on basal acid secretion, both peptides inhibited pentagastrin (0.5 micrograms.kg-1.h-1)- and histamine (0.4 mg.kg-1.h-1)-stimulated acid secretion in a dose-dependent manner. When the metabolic clearance rate for each peptide was taken into account, the 19-37 fragment was as potent as the whole Oxm, regardless of the type of stimulant. When the dose of pentagastrin was increased from 0.175 to 1.1 micrograms.kg-1.h-1, the extent of inhibition induced by Oxm (40 pmol/kg) also increased. In contrast, when the dose of histamine was increased from 0.25 to 1.2 mg.kg-1.h-1, the extent of inhibition induced by Oxm (40 pmol/kg) decreased. Oxm-(19-37) (70-140 pmol/kg) displayed the same behavior as the whole molecule under both types of stimulation.(ABSTRACT TRUNCATED AT 250 WORDS)

1H n.m.r. conformational studies on the C-terminal octapeptide of oxyntomodulin, a beta-turn locked by a salt bridge.

The octapeptide Lys-Arg-Asn-Lys-Asn-Asn-Ile-Ala (Arg4 in the human sequence) is the C-terminal part of porcine oxyntomodulin, an endogeneous peptide which is a potent inhibitor of stimulated acid secretion. This octapeptide exhibits the whole range of biological activities of the parent hormone. In the present work we report an 1H n.m.r. investigation of the conformational properties of the octapeptides of pig and human sequences in dimethylsulfoxide-d6 (DMSO) solution. The various resonances were assigned on the basis of two-dimensional COSY and NOESY experiments. Other experiments such as (i) temperature and concentration dependence of the amide proton chemical shifts, (ii) effects of ionic strength, (iii) comparison of the spectra with different analogues, were performed. We showed that in DMSO, the conformation of the octapeptide is directly related to the ionisation state of the C-terminus carboxyl group of alanine. In carboxylic state, the peptide adopts an extended conformation, while in the carboxylate state the four last residues (Asn-Asn-Ile-Ala) are involved in a type II beta-turn structure probably locked by a salt bridge between the carboxyl group of Ala8 and the epsilon ammonium group of Lys4 (or the guanidinium group of Arg4). These observations provide an insight into the possible conformational tendencies of this peptide in biological media.

Solid-phase peptide synthesis of human(Nle-27)-oxyntomodulin. Preliminary evaluation of its biological activities.

Oxyntomodulin is a peptide isolated from porcine intestine which consists of the whole glucagon sequence extended at its C-terminal part by a basic octapeptide. The analogue (Nle-27)-oxyntomodulin of the human sequence has been synthesized by solid-phase peptide synthesis, purified by HPLC and identified. Its biological activities are the same as those of the natural hormone.

Somatostatin enhances the inhibitory effect of oxyntomodulin and its C-terminal octapeptide on acid secretion.

Somatostatin (SOM) and oxyntomodulin (OXM) are two natural peptides present in the gut which display inhibitory effects on gastric acid secretion in rat. Possible interactions between the effects of these two molecules were tested in the anesthetized rat, using as the stimulant either pentagastrin or histamine at doses that induced 30% of the maximal responses. SOM was tested at sub-threshold doses and OXM at doses inducing an inhibition of less than 50%. SOM induced a highly significant potentiation of the action of OXM both on pentagastrin- and histamine-induced secretion. Similarly, SOM enhanced the inhibitory effects of the C-terminal octapeptide of OXM. Whatever the mechanism involved, this potentiating effect of SOM might be of importance in the in vivo biological effect of OXM.

Oxyntomodulin and its C-terminal octapeptide inhibit liquid meal-stimulated acid secretion.

Oxyntomodulin (OXM), a 37-amino acid glucagon-containing peptide produced mainly in intestine and endocrine pancreas, is present in rat plasma and inhibits pentagastrin-stimulated gastric acid secretion in both the anesthetized and the conscious rat. In order to investigate the modifications in acid and water secretions in a physiological model, we set up a protocol which allowed us to study acid secretion in the conscious rat both under basal conditions (during an 18-hour fast) or after a physiological stimulus (a liquid meal). OXM (110 pmol X kg-1) did not modify the basal acid or water output in an 18-hour fasting state. When injected before the test meal, OXM (225 pmol X kg-1) sharply decreased the acid output stimulated by a liquid meal (milk), which represented 10 times the basal value. Results are compared to those obtained when pentagastrin was the stimulant. Synthetic C-terminal octapeptide of OXM was able to inhibit both basal and meal-stimulated secretions. We can conclude that OXM, or a closely related peptide containing the C-terminal octapeptide, may be a physiological regulator of gastric functions.

Synthesis of the C-terminal octapeptide of pig oxyntomodulin. Lys-Arg-Asn-Lys-Asn-Asn-Ile-Ala: a potent inhibitor of pentagastrin-induced acid secretion.

The synthesis of Lys-Arg-Asn-Lys-Asn-Asn-Ile-Ala representing the C-terminal octapeptide of oxyntomodulin isolated from pig intestine is described. Its structure was confirmed by its 360-MHz 1H NMR spectra. The octapeptide was tested for its ability to inhibit pentagastrin-induced acid secretion, in the anaesthetized rat, in the conscious rat with chronic gastric fistula, and in the conscious cat with gastric chronic fistula. The octapeptide inhibits pentagastrin-induced acid secretion in all three models. Compared to oxyntomodulin, the parent hormone, the synthetic peptide was approximately 150 times less potent but has the same efficacy. Biological data are presented and discussed.

Oxyntomodulin (glucagon-37) and its C-terminal octapeptide inhibit gastric acid secretion.

Oxyntomodulin (OXM) is a peptide isolated from porcine intestine which consists of the whole glucagon sequence with a basic octapeptide (KA8) at its C-terminal end. In this study, the effect of OXM and KA8 on pentagastrin-stimulated gastric acid secretion has been studied in conscious rats and cats. In rats, OXM (25-450 pmol . kg-1) as well as KA8 (7.5-60 nmol . kg-1) inhibited pentagastrin-stimulated gastric acid output in a dose-dependent manner; KA8 was about 100-times less potent than OXM. In cats, KA8 (90 nmol . kg-1) was also an inhibitor of acid secretion. We conclude that OXM, or a closely related peptide, could be a physiological modulator of gastric acid secretion, and that the C-terminal octapeptide of OXM is implicated in this effect.