Pharmacological investigation of the role of ion channels in salivary secretion

The role of K+ and Cl- channels in salivary secretion was investigated, with emphasis on the potential role of Ca2+ -activated K+ channels. Ligand saturation kinetic assays and autoradiography showed large-conductance (BK) K+ channels to be highly expressed in rat submandibular and parotid glands, whereas low-conductance (SK) K+ channels could not be detected. To investigate the role of K+ and Cl- channels in secretion, intact rabbit submandibular glands were vascularly perfused and secretion induced by 10 microM ACh. Secretion was inhibited by 34+/-3% following perfusion with the general K+ channel inhibitor Ba2+ (5 mM), whereas organic inhibitors of BK (200 nM paxilline) or intermediate-conductance (IK) K+ channels (5 microM clotrimazole) had no effect. Secretion was strongly influenced by Cl- channel inhibitors, as 100 microM 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB) completely abolished, while 10 microM NPPB, 20 microM NS1652 and 20 microM NS3623 reduced secretion by 34+/-3%, 23+/-3% and 59+/-4%, respectively. In conclusion, although high expression levels of BK channels were demonstrated, pharmacological tools failed to demonstrate any role for BK, IK or SK channels in salivary secretion in the rabbit submandibular gland. Other types of K+ channel, however, and particularly Cl- channels, are essential for ACh-induced salivary secretion.     

Pharmacological investigation on the role of dopamine in the rat locus coeruleus

The role of dopamine (DA) in the rat locus coeruleus (LC) was investigated by determining the levels of 3,4-dihydroxyphenylacetic acid (DOPAC), DA and noradrenaline (NA) in the LC after pharmacological treatments by pargyline, haloperidol, 6-hydroxydopamine (6-OHDA) and desmethylimipramine (DMI). The DA, DOPAC and NA contents of the LC were determined by high pressure liquid chromatography. Fifteen days after 6-OHDA, the DOPAC and NA levels were reduced by 60%, but they remained constant after 6-OHDA + DMI. Pargyline provoked highly significant increases in DA and NA but reduced DOPAC to non-measurable amounts. Haloperidol caused a 54% decrease in the DOPAC levels. Pargyline and haloperidol administered to rats having received 6-OHDA + DMI 15 days before, caused similar effects on DA, DOPAC and NA levels as those in non-treated rats. It is suggested that DOPAC is mainly located in noradrenergic neurons, thus eliminating the possibility of a significant DA cell body population in the rat LC.     

An investigation into the role of P-glycoprotein in Alzheimer's disease lesion pathogenesis

The pathogenesis of Alzheimer's disease (AD) senile plaque (SP) and neurofibrillary tangle (NFT) lesions putatively involves a compromised blood-brain barrier (BBB). P-glycoprotein (P-gp) is a recognized BBB-related efflux transporter protein. In this investigation we determined the density of SP and NFT lesions and capillary densities stained positively for P-glycoprotein (P-gp), and other transport proteins, in AD and control group (CG) brain samples. Our results indicate that there are significant negative correlations (p<.01) between the densities of NFT and SP(40) lesions and P-gp positive capillaries in AD but not CG brain samples. Significant positive correlations (p<.01) were observed between the densities of P-gp positive capillaries and LRP and RAGE positive capillaries in both AD and CG brains. These results also suggest that the levels of capillary P-gp may contribute to AD lesion development and that the role of P-gp is associated with that of LRP and RAGE.     

The role of the serotoninergic system in the pathogenesis of experimental ulcerous colitis

Ulcerous colitis was modeled in a rat experiment by introducing picrylsulfonic acid. The role of serotoninergic structures in the pathogenesis of ulcerous colitis was studied by preliminary administration of serotonin or spiperone, a 5-HT2 serotonin blocker. Spiperone was shown to inhibit the damaging action of picrylsulfonic acid during the first ten days of the beginning of modeling, and to accelerate reparative processes.     

The role of leukotrienes in airway inflammation

Cysteinyl leukotrienes (cysLTs) are a class of closely structurally related lipid molecules, originally described as slow-reacting substance of anaphylaxis, with a myriad of biologic functions. These activities include producing smooth muscle contraction and mucus secretion, recruiting allergic inflammatory cells, modulating cytokine production, influencing neural transmission, and altering structural changes in the airway. Administration of cysLTs to animals and human subjects reproduces many features of allergic inflammation and asthma. Leukotriene (LT) blockers have independent efficacy in asthma and improve pulmonary function when added to inhaled steroids. Conversely, blockade of this pathway both in animals and in human subjects results in important reductions in inflammation and its consequences and might reduce structural changes of remodeling. These data collectively make a compelling case for an important role of cysLTs in airway inflammation and asthma. However, the magnitude of effect of anti-LTs is smaller than that of corticosteroids, and there is more variability in benefit of LT blockade than is seen with inhaled steroids. In addition, adding anti-LTs to inhaled steroids in asthmatic patients does not appear to produce added anti-inflammatory benefit. Genetic polymorphisms and environmental factors, such as tobacco smoke exposure, might underlie some of the heterogeneity of response to LT blockers.     

The role of leukotrienes in allergic rhinitis.

OBJECTIVE: To review the role of cysteinyl leukotrienes (cysLTs) in allergic rhinitis and the scientific rationale for therapy with leukotriene receptor antagonists (LTRAs). DATA SOURCES: Relevant basic science and clinical articles were identified by a search of the PubMed database for articles published from 1984 to 2004 using the following keywords: allergic rhinitis; nose; immune response; allergen challenge; leukotrienes C, D, and E; cysteinyl leukotriene; cysteinyl leukotriene receptor; cytokine; leukocyte; montelukast; zafirlukast; and pranlukast. STUDY SELECTION: The authors' expert opinion was used to select studies for inclusion in this review. RESULTS: CysLTs are synthesized via 5-lipoxygenase metabolism of arachidonic acid by mast cells and basophils during the early-phase response to antigen and by eosinophils and macrophages during the late phase. The cysLT levels in nasal secretions are elevated after short-term allergen instillation and in allergy season in patients with allergic rhinitis. These lipid mediators act locally and systemically by interacting with receptors, particularly the cysLT1 receptor, on target cells. Evidence derived from topical application of cysLTs in the nose and from the effects of LTRAs indicates that cysLTs contribute to nasal mucous secretion, congestion, and inflammation. CysLTs promote allergic inflammation by enhancing immune responses and the production, adhesion, migration, and survival of inflammatory cells such as eosinophils. They also increase the generation of an array of other proinflammatory mediators, such as cytokines, which in turn increase the production of and receptors for cysLTs. Clinical trials have demonstrated that LTRAs have significant but modest efficacy as single agents but additive efficacy when used with other classes of agents. CONCLUSIONS: CysLTs fulfill the criteria for relevant mediators of allergic rhinitis via their diverse effects on immune, inflammatory, and local structural components of disease. By blocking the cysLT1 receptor responsible for most of these effects, LTRAs represent a useful approach to treatment of this important and prevalent disorder.     

A role for natural regulatory T cells in the pathogenesis of experimental cerebral malaria

Cerebral malaria (CM) is a serious complication of Plasmodium falciparum infection that is responsible for a significant number of deaths in children and nonimmune adults. A failure to control blood parasitemia and subsequent sequestration of parasites to brain microvasculature are thought to be key events in many CM cases. Here, we show for the first time, to our knowledge, that CD4(+)CD25(+)Foxp3(+) natural regulatory T (Treg) cells contribute to pathogenesis by modulating immune responses in P. berghei ANKA (PbA)-infected mice. Depletion of Treg cells with anti-CD25 monoclonal antibody protected mice from experimental CM. The accumulation of parasites in the vasculature and brain was reduced in these animals, resulting in significantly lower parasite burdens compared with control animals. Mice lacking Treg cells had increased numbers of activated CD4(+) and CD8(+) T cells in the spleen and lymph nodes, but CD8(+) T-cell recruitment to the brain was selectively reduced in these mice. Importantly, a non-Treg-cell source of interleukin-10 was critical in preventing experimental CM. Finally, we show that therapeutic administration of anti-CD25 monoclonal antibody, even when blood parasitemia is established, can prevent disease, confirming a critical and paradoxical role for Treg cells in experimental CM pathogenesis.     

A pharmacological study on the role of nitric oxide in the pathogenesis of experimental allergic encephalomyelitis

Objective and Design: The study examines the effects of nitric oxide synthase (NOS) inhibitors on the development of neurological EAE and the levels of nitrite in the central nervous system (CNS) during established disease. Materials: EAE was induced inmale Lewis rats (200–250 g). Treatment: Ras received N^G-nitro-L-arginine methyl ester (L-NAME) (30 mg/kg body weight) day 7 to 12 post-inoculation (P.I.), 7-nitroindazole (10 mg/kg) day 7 to 11 P.I. or aminoguanidine (200 or 400 mg/kg) day 1 to 12 P.I. Methods: Neurological symptoms were assessed and CNS cytosol nitrite and protein levels measured. Results were analysed using the Mann Whitney U-test and the Fischer exact probability test. Results: Symptoms of EAE were associated with a significant elevation in CNS nitrite (P<0.001). Treatment with NOS inhibitors caused a marked reduction in nitrite levels (p<0.00). However, in some experiments, vehicle administration also reduced CNS nitrite content (p<0.05). Although neurological disease was supressed in EAE-sensitised rats receiving L-NAME (2±0.3 vs 3±0.3 mean peak severity ±SEM) and 7-nitroindazole (1±0.3 vs 3±0.3, p<0.01) comparable inhibition was achieved by respective vehicle treatment (p<0.01). In contrast, neither aminoguanidine nor corresponding vehicle altered disease development. Conclusions: Drug-induced reductions in CNS nitrite levels during EAE are not always associated with a suppression of neurological symptoms, which suggests NO is not of primary importance in disease pathogenesis. In addition, the study emphasises the strict requirement for appropriate controls when assessing the efficacy of drugs on the course of EAE. accepted by M. J. Parnham     

Possible role of capillary action in pathogenesis of experimental catheter-associated dermal tunnel infections.

An animal model of vascular-catheter-associated dermal tunnel infections was developed to study the pathogenesis of such infections. Bacteria inoculated onto entry sites of catheters into skin could be identified by culture and Gram stain on the tips of plastic catheters (4 cm from the entry site) within 1 h of inoculation, whether the animal was inoculated at the time of insertion of the catheter or 1 week afterwards. Histological examination of dermal tunnels revealed that the introduction of bacteria preceded the development of tissue inflammation. Bacteria on entry sites of percutaneous catheters moved rapidly from the entry site into the dermal tunnel along the external catheter surface, perhaps suspended in a fluid phase and propelled by capillary action.     

A possible role for leukotrienes in the regulation of glomerular haemodynamic in the dog

In anaesthetized beagles, saralasin, phentolamine, 1-penicillamine-2-O-methyl-tyrosine-8-arginine-vasopressin and SCH 23390, a DA₁ antagonist, were infused into the left renal artery (i.r.a) and indomethacin and aprotinin intravenously (Group 1). In Groups 2 and 3, i.r.a infusion of two chemically different putative leukotriene (LT) antagonists, FPL 55712 (100 g/kg/min) and LY 171883 (500 g/kg/min), respectively, was superimposed in the fourth period of experiments. In comparison to Group 1, there was an increase (40% in Group 2 and 33% in Group 3) in renal blood flow and a decrease in glomerular filtration rate (16% and 17%, respectively) and filtration fraction (36% and 41%, respectively). Similar changes were observed on the single nephron level. Directly measured glomerular capillary pressure decreased by 10% and 12%, respectively. A decrease in total arteriolar resistance by 34% and 25%, respectively, was caused by a comparatively higher decrease in efferent (44% and 34%, respectively) than afferent (26% and 15%, respectively) arteriolar resistance values. No change in the ultrafiltration coefficient,K _f, was detected. Providing FPL 55712 and LY 171883 are specific LT antagonists, these experiments suggest a possible constrictory role of LT (expressed more on the efferent than afferent arteriole) in anaesthetised mildly surgical stressed dogs.