Elevated Nasal Mucosal G Protein Levels and Histamine Receptor Affinity in a Guinea Pig Model of Nasal Hyperresponsiveness

Abstract

Background: Nasal hyperresponsiveness is a common feature of allergic rhinitis, but the underlying mechanisms have yet to be elucidated. The effects of repeated antigen inhalation on the characteristics of histamine H₁ receptors and expression levels of heterotrimeric guanosine 5′-triphosphate-binding proteins in nasal mucosa were investigated to understand the mechanisms of the pathogenesis of nasal hyperresponsiveness in allergic rhinitis. Methods: Male Hartley guinea pigs were sensitized by the inhalation of dinitrophenylated ovalbumin antigen (10 mg of protein/ml) and repeatedly challenged by inhaling aerosolized dinitrophenylated ovalbumin antigen for 3 weeks. Twenty-four hours after the last antigen inhalation, in vivo nasal responsiveness to histamine was measured. [³H]Mepyramine binding assays and immunoblotting for α subunits of the G_q protein were also performed using membrane preparations of isolated nasal mucosae. Results: The histamine-induced increase in intranasal pressure was significantly augmented after repeated antigen challenge, indicating that nasal hyperresponsiveness was achieved. In saturation binding studies, no significant change was observed in the density and antagonist affinity of H₁ receptors in the hyperresponsive animals. On the other hand, the affinity of histamine for high-affinity agonist binding sites in the hyperresponsive group, measured by histamine competition binding studies, was much greater than that in control animals, and these results were affected by guanosine 5′-O-(3-thiotriphosphate) in both groups. Moreover, Gα_q levels in nasal mucosal homogenates were significantly increased after repeated antigen challenge. Conclusions: Elevated G protein levels in nasal mucosa might induce an increased binding affinity of histamine to its receptors, resulting in an augmented nasal response to histamine, that is, nasal hyperresponsiveness, in guinea pigs.

Increased Expression of Inducible Nitric Oxide Synthase in Nasal Mucosae of Guinea Pigs with Induced Allergic Rhinitis

“…This study clearly showed an increased expression of iNOS in nasal mucosa of a guinea pig allergic rhinitis model. 12 On the other hand, no change in the expression levels of eNOS and nNOS in nasal mucosa was observed in this animal model of allergic rhinitis. The results might be consistent with previous reports in upper and lower airways in allergy, 13,19,20 suggesting that iNOS may play an important role in the pathogenesis of allergic airway diseases, such as asthma and rhinitis.…”

“…An allergic rhinitis model was prepared as previously reported. 12 In brief, guinea pigs were sensitized by inhalation of dinitrophenylated ovalbumin antigen (DNP-OVA; 10 mg of protein/mL) with an ultrasonic nebulizer (TUR-3000; Nihon Kohden, Tokyo, Japan) for 10 minutes under the unanesthetized condition in a Plexiglas box (300 ϫ 200 mm, 150-mm height; day 0). Seven days after the sensitization (day 7), the animals were boosted by the same inhalation procedure described previously.…”

“…The previous study showed an augmented histamine-induced increase in intranasal pressure in the repeatedly antigen-challenged guinea pigs. 12 To clarify the mechanism(s) of the augmented in vivo histamine responsiveness, the in vitro histamine responsiveness of mucosal tissues of nasal septa isolated from the repeatedly antigen-challenged guinea pigs was compared with that from the sensitized control animals. As shown in Fig.…”

“…In this study, the changes in the expression levels of NOS isoforms in nasal mucosae were determined in guinea pigs with induced allergic rhinitis. 12 Moreover, the NO-mediated vascular relaxation of nasal mucosa isolated from this animal model, which has an in vivo nasal hyperresponsiveness, 12 was compared with that from control guinea pigs.…”

New concepts of histamine receptors and actions

“…In addition, the nasal hyperresponsiveness in chronic allergic rhinitis might be explained in part by an elevation of G-protein levels that might increase the binding affinity of histamine to its receptors, increase recycling of functional H1-R to the cell surface after activation, or promote H1-R-G-protein coupling. These mechanisms could augment histamine-induced nasal responses [14].…”