alpha(1)-adrenoceptor subtypes and effect of alpha(1A)-adrenoceptor agonist NS-49 on guinea pig nasal mucosa vasculature

Immunohistochemical localization of alpha and beta adrenergic receptors in the human nasal turbinate

OBJECTIVE

Adrenergic receptors (ARs) include four general types (α1, α2, β1 and β2), which are found in different target tissues. α-AR agonists are commonly used for decongestant therapy of upper airway diseases. In order to clarify the roles of AR subtypes in the upper airways, we investigated the localization of these receptors by immunohistochemistry.

METHODS

Human turbinates were obtained after turbinectomy from 12 patients with nasal obstruction refractory to medical therapy. The specific cells expressing α- and β-AR proteins were identified by immunostaining using an anti-human AR subtype-specific antibodies (α1A-, α1D-, α2C- and β2-ARs) antibody.

RESULTS

Immunohistochemical analysis revealed that immunoreactivities for α1D- and β2-ARs were densely distributed in submucosal glands. In contrast, immunoreactivities for α1A- and 2C-ARs were densely distributed in vascular smooth muscle.

CONCLUSION

Our results suggested that adrenergic receptor (AR) subtypes had different roles in upper airway diseases, such as allergic rhinitis and nonallergic rhinitis.

Scientific rationale for the use of alpha-adrenergic agonists and glucocorticoids in the therapy of pediatric stridor

Purpose. The most common pharmacological therapies used in the treatment of stridor in children are glucocorticosteroids (GC) and alpha-adrenergic (αAR) agonists. Despite the long-standing reported efficacy of these medications, there is a paucity of data relating to their actual mechanisms of action in the upper airway. Summary. There is compelling scientific evidence supporting the use of αAR-agonists and GCs in pediatric stridor. αAR signaling and GCs regulate the vasomotor tone in the upper airway mucosa. The latter translates into better airflow dynamics, as delineated by human and nonhuman upper airway physiological models. In turn, clinical trials have demonstrated that GCs and the nonselective αAR agonist, epinephrine, improve respiratory distress scores and reduce the need for further medical care in children with stridor. Future research is needed to investigate the role of selective αAR agonists and the potential synergism of GCs and αAR-signaling in the treatment of upper airway obstruction and stridor.

Alpha-adrenergic mRNA subtype expression in the human nasal turbinate

PURPOSE

Alpha-adrenergic receptor (AR) agonist drugs (e.g., epinephrine) are commonly used for upper airway procedures, to shrink the mucosa, retard absorption of local anesthetic agents, and improve visualization by limiting hemorrhage. Decongestant therapy often also includes alphaAR agonist agents, however overuse of these drugs (e.g., oxymetazoline) can result in chronic rhinitis and rebound increases in nasal secretion. Since current decongestants stimulate alphaARs non-selectively, characterization of alphaAR subtype distribution in human airway (nasal turbinate) offers an opportunity to refine therapeutic targets while minimizing side-effects. We, therefore, investigated alphaAR subtype expression in human nasal turbinate within epithelial, duct, gland, and vessel cells using in situ hybridization.

METHODS

Since sensitive and specific anti-receptor antibodies and highly selective alphaAR subtype ligands are currently unavailable, in situ hybridization was performed on sections of three human nasal turbinate samples to identify distribution of alphaAR subtype mRNA. Subtype specific (35)S-labelled mRNA probes were incubated with nasal turbinate sections, and protected fragments remaining after RNase treatment analyzed by light and darkfield microscopy.

RESULTS

In non-vascular tissue alpha(1d) AR mRNA predominates, whereas notably the alpha(2c) is the only alphaAR subtype present in the sinusoids and arteriovenous anastamoses.

CONCLUSION

Combined with the current understanding that AR-mediated constriction of nasal sinusoids underpins decongestant therapies that minimize secretions and shrink tissues for airway procedures, these findings suggest that alpha(2c) AR subtypes provide a novel selective target for decongestant therapy in humans.

Impaired norepinephrine-mediated contraction of isolated nasal mucosa in guinea pigs with allergic rhinitis

BACKGROUND

One of the causes of nasal obstruction associated with allergic rhinitis probably is caused by the dilatation of plexus cavernosum in nasal mucosa. In this study, the change in vascular responsiveness of nasal mucosa was investigated in the septal mucosae isolated from guinea pigs with allergic rhinitis.

METHODS

An allergic rhinitis model was prepared in guinea pigs by repeated challenge with aerosolized dinitrophenylated-ovalbumin antigen. Twenty-four hours after the last antigen challenge, the changes in the isometrical tension of isolated nasal septal mucosa were measured.

RESULTS

In isolated nasal mucosal tissues, both norepinephrine (NE) and leukotriene D4 caused concentration-dependent contractile and relaxant responses, respectively. The NE-induced contractile response was significantly attenuated in nasal mucosae of the repeatedly antigen challenged guinea pigs. The mucosal relaxation induced by leukotriene D4 was slightly attenuated in this animal model of allergic rhinitis.

CONCLUSION

This study shows an attenuation of NE-induced contraction of isolated nasal mucosa in the antigen-exposed guinea pigs. The impaired contractile response mediated by sympathetic alpha-adrenoceptors of nasal blood vessels might be involved in the development of nasal obstruction in allergic rhinitis.

Comparison of norepinephrine responsiveness of mucosal veins in vivo with that of isolated mucosal tissue in vitro in guinea pig nasal mucosa

BACKGROUND

The vascular responsiveness of nasal mucosa has been determined frequently by using isolated mucosal tissues although it is not clear whether the response of the whole tissue truly reflects the response of the vasculature (especially veins) in mucosa. In this study, the in vivo responsiveness of mucosal veins was compared with in vitro responsiveness of isolated mucosal tissue in guinea pig nasal septa.

METHODS

The in vivo venous responsiveness to norepinephrine (NE) of guinea pig nasal septal mucosa was measured by changes in the diameters of mucosal veins, stereomicroscopically. The in vitro responsiveness to NE of isolated nasal septal mucosae from guinea pigs also was determined by standard organ-bath technique.

RESULTS

Application of NE induced concentration-dependent contractile responses both in vivo and in vitro with the pD2 (negative logarithm for 50% effective concentration [M] of NE) values of 5.23 +/- 0.29 and 5.00 +/- 0.17, respectively.

CONCLUSION

The equal potencies obtained by the in vivo and in vitro experiments suggest that an increase in tension of isolated nasal mucosal tissue might be caused by the contraction of mucosal veins. Both the in vivo and the in vitro methods used in this study might be useful for determining vasoreactivity of nasal mucosa in experimental animals.

Regional differences in vascular responsiveness of nasal mucosae isolated from naive guinea pigs

OBJECTIVE

In the present study, the contractile response to norepinephrine (NE) and relaxing response to histamine and leukotriene D(4) (LTD(4)) were compared among the nasal mucosae of septa (S) and lateral (L) and medial turbinates (M) isolated from naive male Hartley guinea pigs.

METHODS

The isometrical tension of the isolated nasal mucosae of the above regions was measured at a resting tension of 0.5 g by using a standard organ-bath technique.

RESULTS

In each mucosal strip, NE induced a contraction in a concentration-dependent manner. A significant difference in efficacy (maximal response) of NE was found (L>M>S). In mucosal strips precontracted with NE (3x10(-5)M), both histamine and LTD(4) induced relaxing responses. The efficacy of histamine in S was significantly greater than those in L and M. The potency order of LTD(4) was L>M>S; a significant difference was observed between L and S.

CONCLUSION

In conclusion, the present study demonstrated a distinct regional difference in the response to contractile and relaxant agonists of isolated nasal mucosae of guinea pigs.

Role of perivascular sympathetic nerves and regional differences in the features of sympathetic innervation of the vascular system

Maintenance of blood pressure is mostly dependent on sympathetic "tone", and the sympathetic nerve innervates the entire vascular bed, excepting the capillaries. Although norepinephrine (NE) is the principal neurotransmitter released upon sympathetic nerve stimulation, neuropeptide Y and ATP are cotransmitters in various vascular tissues. In addition, dopamine and epinephrine, as well as acetylcholine, have been shown to be sympathetic neurotransmitters in specific vasculatures. Transmitter NE release is modified by a number of endogenous substances including the transmitter itself. Chronic denervation of the preganglionic fiber induces an increase in NE release per pulse, indicating postganglionic neuronal supersensitivity. So far, three main adrenoceptor types have been shown, alpha1, alpha2 and beta, each of which is further divided into at least three subtypes, as well as the alpha1L-adrenoceptor, a phenotype of the cloned alpha1a-adrenoceptor, in the blood vessel. Thus, the response of vessels with different receptor types to a transmitter varies quantitatively and even qualitatively from one vessel to another. The remarkable diversity in the sympathetic innervation mechanism in the vascular system may play an important role in regional variations in the regulation of blood flow. The sympathetic nerve also exerts long-term trophic action on the blood vessel. In conclusion, the sympathetic nervous system plays an important role not only in the regulation of cardiovascular dynamics but in the maintenance of the vessel structure, as well.

Effect of JTH-601, a putative alpha(1L)-adrenoceptor antagonist, on guinea pig nasal mucosa vasculature

The existence of alpha(1)-adrenoceptors with low affinity for prazosin, an alpha(1L) subtype, has been proposed in addition to alpha(1)-adrenoceptor subtypes with high affinity for prazosin, i.e. the alpha(1H) group: alpha(1A), alpha(1B) and alpha(1D) subtypes. In the present study, we investigated the effect of JTH-601 (3-(N-[2-(4-hydroxy-2-isopropyl-5-methylphenoxy)ethyl]-N-methylaminomethyl)-4-methoxy-2,5,6-trimethylphenol hemifumarate), a putative alpha(1L)-adrenoceptor antagonist, on the isolated guinea pig nasal mucosa vasculature. JTH-601 (0.01-0.03 microM) competitively antagonized the noradrenaline-induced contraction of the tissue in a concentration-dependent manner. The pA(2) value for JTH-601 was 8.14 +/- 0.04 (means +/- SEM, n = 6). The data suggests that the alpha(1L)-subtype is involved in the noradrenaline-induced contraction of the guinea pig nasal mucosa vasculature.

Effect of hydrogen peroxide on guinea pig nasal mucosa vasculature

The effect of hydrogen peroxide (H2O2) on guinea pig nasal mucosa vasculature was studied by in vitro assay. H2O2 elicited relaxation of guinea pig nasal mucosa strips precontracted with phenylephrine in a concentration-dependent manner. The relaxant response to H2O2 was abolished in the presence of catalase. Preincubation of the strips with N(G)-nitro-L-arginine methyl ester or methylene blue significantly attenuated the relaxant responses elicited by H2O2. Fluorescence caused by DAF-2 DA, a fluorescence indicator for nitric oxide, was observed along the nasal mucosa vasculature in response to H2O2. These results suggest that H2O2 induced relaxation of the guinea pig nasal mucosa vasculature and that this relaxation is mediated by the NO/cGMP pathway.