REPORTS OF ORIGINAL INVESTIGATIONS
`
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`
`Alpha-adrenergic mRNA subtype expression in
`the human nasal turbinate
`[Expression du sous-type d’ARN messager alpha-adrénergique dans le cornet
`nasal humain]
`Mark Stafford-Smith MD,* Raquel Bartz MD,*† Katrina Wilson,* James N. Baraniuk MD,§
`Debra A. Schwinn MD*†‡
`
`Purpose: Alpha-adrenergic receptor (AR) agonist drugs (e.g.,
`epinephrine) are commonly used for upper airway proce-
`dures, to shrink the mucosa, retard absorption of local anes-
`thetic agents, and improve visualization by limiting hemorrhage.
`Decongestant therapy often also includes αAR 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 αARs non-selectively, charac-
`terization of αAR subtype distribution in human airway (nasal
`turbinate) offers an opportunity to refine therapeutic targets
`while minimizing side-effects. We, therefore, investigated αAR
`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 αAR subtype ligands are currently unavail-
`able, in situ hybridization was performed on sections of three
`human nasal turbinate samples to identify distribution of αAR
`subtype mRNA. Subtype specific 35S-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 α1d AR mRNA predominates,
`whereas notably the α2c is the only αAR subtype present in the
`sinusoids and arteriovenous anastamoses.
`Conclusion: Combined with the current understanding that
`AR-mediated constriction of nasal sinusoids underpins decon-
`gestant therapies that minimize secretions and shrink tissues for
`airway procedures, these findings suggest that α2c AR subtypes
`provide a novel selective target for decongestant therapy in
`humans.
`
`CAN J ANESTH 2007 / 54: 7 / pp 549–555
`
`Objectif : Les médicaments agonistes des récepteurs alpha-
`adrénergiques (AR) (par ex., l’épinéphrine) sont communément
`utilisés lors des interventions sur les voies aériennes supérieures,
`afin de rétrécir la muqueuse, de retarder l’absorption d’agents
`anesthésiques locaux et d’améliorer la visualisation en limitant
`l’hémorragie. Un traitement décongestionnant inclut également
`souvent des agents agonistes αAR ; toutefois, la surutilisation
`de ces médicaments (par ex., l’oxymétazoline) peut engendrer
`une rhinite chronique et l’augmentation rebond des sécrétions
`nasales lors de la cessation du traitement. Puisque les déconges-
`tionnants actuels stimulent les αAR de manière non-sélective, la
`caractérisation de la distribution des sous-types d’αAR dans les
`voies aériennes de l’homme (cornet nasal) offre la possibilité de
`perfectionner les cibles thérapeutiques tout en minimisant les
`effets secondaires. C’est pourquoi nous avons examiné l’expression
`des sous-types d’αAR au niveau du cornet nasal humain dans les
`cellules épithéliales, du canal, des glandes et des vaisseaux, à l’aide
`d’une hybridation in situ.
`Méthode : Étant donné que des anticorps anti-récepteurs sen-
`sibles et spécifiques ainsi que des ligands très sélectifs des sous-
`types d’αAR sont disponibles actuellement, l’hybridation in situ
`a été effectuée sur des sections de trois échantillons de cornet
`nasal humain afin d’identifier la distribution d’ARN messager des
`sous-types d’αAR. Des sondes d’ARN messager marquées au 35S
`et spécifiques au sous-type ont été incubées avec des sections de
`cornet nasal, et les fragments protégés restants après le traitement
`à la ribonucléase ont été analysés par microscopie optique et sur
`fond noir.
`Résultats : Dans les tissus non-vasculaires, l’ARN messager AR
`α1d est prédominant, alors que le α2c est notablement le seul
`sous-type d’αAR présent dans les sinusoïdes et les anastomoses
`artérioveineuses.
`
`From the Departments of Anesthesiology,* Pharmacology/Cancer Biology, & Medicine (Pulmonary and Cardiology),† and Surgery,‡
`Duke University Medical Center, Durham, North Carolina; and the Departments of Medicine and Pediatrics,§ Georgetown University,
`Washington, DC, USA.
`Address correspondence to: Dr. Mark Stafford-Smith, Department of Anesthesiology, Duke University Medical Center, Box 3094,
`DUMC, Durham, NC 27710, USA. Phone: 919-681-5046; Fax: 919-681-8993 ; E-mail: staff002@mc.duke.edu
`Funding: This study was funded in part by NIH grant #HL49103 (DAS) and an educational grant from Proctor & Gamble. Tissue was
`provided by Drs. Rasmussen-Ortega and Stephen B. Liggett.
`Accepted for publication February 16, 2007.
`Revision accepted April 9, 2007.
`
`
`
`
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`Conclusion : On considère maintenant que la constriction des
`sinus nasaux médiée par AR est à la base des thérapies de décon-
`gestion qui minimisent les sécrétions et rapetissent les tissus lors
`des interventions sur les voies aériennes. Ces résultats suggèrent
`donc que les sous-types d’AR α2c fournissent une nouvelle cible
`sélective pour les traitements de décongestion chez les humains.
`
`ALPHA-ADRENERGIC receptors (αARs)
`
`are commonly used for upper airway proce-
`dures, to shrink the mucosa, retard absorp-
`tion of local anesthetic agents, and improve
`visualization by limiting hemorrhage, and also play
`a key role in the pharmacologic treatment of nasal
`congestion, rhinorrhea, and epistaxis. Stimulation of
`α-receptors on the nasal erectile apparatus leads to
`constriction of arteriovenous anastomoses and col-
`lapse of venous sinusoids (Figure 1). The result is a
`decrease in the thickness of the nasal mucosa and so
`an increase in the nasal cross-sectional area of airflow
`within the bony confines of the nostrils. These effects
`are mediated in vivo by the sympathetic innervation,
`and therapeutically by oral and topical sympatho-
`mimetics. Effects on epithelial cell ciliary function
`and glandular exocytosis have also been reported.1
`Withdrawal of sympathetic effects leads to vasodila-
`tion of the arteriovenous anastomoses and engorge-
`ment of the venous sinusoids. The result is thickening
`of the nasal mucosa, reduction of cross-sectional area
`for airflow, and nasal obstruction. Prolonged use of
`topical sympathomimetics such as oxymetazoline and
`zylometazoline may lead to rebound vasodilation, cili-
`ary dysfunction, and increased glandular secretion in
`the condition of rhinitis medicamentosa.2–6
`Nasal αARs have been described previously.
`However, the specific α1 subtypes (α1a, α1b, α1d) and
`α2 subtypes (α2a - formerly α2C10, α2b - formerly
`α2C2, α2c - formerly α2C4) that are present and their
`differential distribution on the epithelium, submuco-
`sal glands, arteriovenous anastomoses, post-capillary
`venules that regulate vascular permeability and leuko-
`cyte infiltration, and venous sinusoids have not been
`determined.7–9 Currently available partially selective
`α1- and α2-agonists and endogenous norepinephrine
`are nonselective for these receptors. In addition,
`αAR subtype distribution is remarkably heterogenous
`among cell types in different tissues and mammalian
`species.10–13 We hypothesize that understanding the
`distribution of each receptor subtype on nasal tissues
`may lead to more specific decongestant targets capable
`of providing benefit while minimizing worrisome
`side-effects.
`
`CAN J ANESTH 54: 7 www.cja-jca.org July, 2007
`
`FIGURE 1 Diagrammatic representation of nasal turbi-
`nate cytoarchitecture. The nasal turbinates have concentric
`epithelial, superficial vascular, submucosal gland, and deep
`erectile tissues. Dilation of the venous sinusoids increases
`the thickness of the mucosa and decreases the cross-section-
`al area of airflow (left half of diagram). Vasoconstriction of
`the arteriovenous anastomoses and myoepithelial cells of
`the sinusoidal walls cause sinusoid collapse, thinning of the
`mucosa, and an increase in the cross-sectional area of air-
`flow (right half of diagram).
`
`Identifying cell specific distribution of αAR sub-
`types within nasal tissue should facilitate novel phar-
`macologic targeting directed at the common and
`vexing problem of nasal decongestion. Because highly
`subtype specific antibodies for αAR subtypes remain
`unavailable, we examined αAR subtype distribution
`using in situ hybridization on human nasal turbinate
`tissue.
`
`Materials and methods
`Nasal turbinate tissue preparation and detection of αAR
`subtype mRNA
`Institutional Review Board (IRB) approval and indi-
`vidual patient consent was obtained for access to
`explanted nasal turbinate tissue from three individu-
`als undergoing endoscopic nasal surgery; in addition,
`IRB approval was obtained at the institution where
`laboratory studies were performed. Tissue samples
`were immediately placed in liquid nitrogen and stored
`at -70oC. Ten µm horizontal frozen sections were cut
`on a cryostate (Leitz Kryostat 1720 digital, Wetzlar,
`Germany) using a -20oC block, thaw mounted onto
`sialylated microscope slides, and stored at -70oC with
`desiccant until further use. Radiolabelled single strand-
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`551
`
`ed sense (control) and antisense (specific) RNA probes
`were made using linearized cDNA constructs, [35S]-
`αUTP (Dupont, NEN, Boston, MA, USA) and either
`SP6 or T7 RNA polymerase, as previously described;
`mRNA probes and controls for in situ experiments
`have been previously validated in our laboratory.12–14
`
`In situ hybridization
`Frozen slide mount sections were warmed to room
`temperature then rinsed for five minutes with 2 ×
`SSC (1 × SSC = 0.15M NaCl, 0.04M Na citrate, pH
`7.2). No permeabilization or prehybridization steps
`were performed. Hybridization buffer (0.02M DTT,
`1x Denhart’s solution (Sigma, St. Louis, MO, USA),
`1 mg·mL–1 salmon sperm DNA (Sigma) heated to
`80oC before use, 50 µg·mL–1 transfer RNA (Sigma),
`2 × SSC, 50% formamide, 9% dextran sulfate), and
`5000–7000 cpm·µL–1 linearized radiolabelled probe
`were applied to the slides. The slides were then incu-
`bated at 50oC overnight in sealed plastic containers
`lined with Whatman filter paper soaked with 50%
`formamide in 2 × SSC buffer to prevent evapora-
`tion of hybridization solution. To remove non-spe-
`cific binding, slides were washed as follows: sequential
`immersion in 1 µL·mL–1 β-mercaptoethanol solutions
`in 2 × SSC (50oC, brief dip) and 50% formamide
`in 2 × SSC (50oC, ten then 20 min), followed by
`RNase treatment using 10 µg·mL–1 RNase in 2 × SSC
`(35oC, 30 min). Subsequent washes included the fol-
`lowing: 2 × SSC (RT, five minutes), 50% formamide
`in 2 × SSC (50oC, five minutes), and 2 × SSC (ten
`minutes), followed by dehydration steps using two-
`minute immersions each in 0.3M ammonium acetate
`solutions containing 50%, 70%, and finally pure 100%
`ethanol. After air drying for 30–60 min, slides were
`then dipped in warm (40oC) autoradiography emul-
`sion (Kodak NTB2, Rochester, NY, USA) in a dark-
`room illuminated with a Kodak safelight #2, dried for
`several hours in the dark, and placed in light-sealed
`slide boxes with desiccant at 4oC for four weeks. After
`warming for 90 min to room temperature, exposed
`slides were developed under a safelight by sequential
`immersion in fresh D19 developer (Kodak) mixed 1:1
`with distilled water (dH2O at 15oC, four minutes) fol-
`lowed by room temperature immersions in dH2O (20
`sec), fixer (Kodak) (five minutes), and dH2O rinses
`(3 × five minutes). Slides were counterstained with
`hematoxylin and eosin, dehydrated in an ascending
`ethanol and xylene series, and coverslips added. Dry
`slides were examined and photographed under light
`and dark field microscopy using Lietz Leica (Wetzlar,
`Germany), WILD M420 (low power), and DMR
`(high power) microscopes at 100X.
`
`CAN J ANESTH 54: 7 www.cja-jca.org July, 2007
`
`TABLE I Darkfield and brightfield semiquantitative grad-
`ing system to assess relative presence of αAR subtype
`mRNA within human nasal turbinate
`
`Grade Darkfield
`
`0
`+/-
`
`+
`++
`
`background
`very low density of
`individual grains
`low density of individual grains
`moderate density of grains
`
`high density grains and clusters
`+++
`high density clusters
`++++
`αAR = alpha-adrenergic receptor.
`
`Brightfield
`
`background
`background
`
`individual grains
`patterns of individual
`grains
`clusters of grains
`high density of grains
`
`Controls
`In order to ensure that detected signal represents
`specific probe hybridization, several positive and
`negative controls were performed. Since human nasal
`turbinate tissue was limited, each probe used in this
`study was carefully tested in experiments with human
`spinal cord using antisense human β-actin as a positive
`control.12,13 Negative controls included verifying lack
`of signal with sense probes and demonstration of loss
`of signal in known positive samples exposed to excess
`RNase [in situ experiments using excess (50 µg·mL–1)
`RNase in washes]. Controls for αAR subtype specific-
`ity of antisense probes included simultaneously per-
`formed in situ experiments with known positive and
`negative non-nasal turbinate tissues.
`
`Detection and analysis
`Due to the thickness of the nasal turbinate specimens,
`a standard quantitative method previously used in
`our lab was found to be unreliable.13 Instead, rela-
`tive quantification of mRNA probe hybridization was
`recorded by two separate blinded observers using the
`presence of silver grains within specific nasal turbinate
`specific cell types - epithelium, ducts, glands, and/or
`vessels. Negative controls included sense probe experi-
`ments on the same tissue. Sections were scored by the
`intensity of silver grain density relative to background
`(Table I).
`
`Results
`There was excellent concordance (> 90%) between
`the two observers’ independent scoring of relative
`intensities of silver grains for the different nasal tur-
`binate samples. Furthermore, there was no evidence
`of non-specific signalling in positive control samples.
`Table II summarizes observations for specific cell
`types and all αAR subtype mRNAs. While all six AR
`subtype mRNAs are present in human nasal turbinate,
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`TABLE II Relative presence of αAR subtype mRNA within human nasal turbinate
`
`αAR subtype
`
`Epithelium
`
`Glands
`
`Vessels
`
`GC
`
`CC
`
`BC
`
`+
`
`0
`
`0
`
`+
`
`0
`
`0
`
`Ducts
`
`SD
`
`0
`
`+
`
`MD
`
`0
`
`0
`
`SG
`
`0
`
`++
`
`MG
`
`++
`
`+++
`
`α1a
`
`α1b
`
`α1d
`
`α2a
`
`α2b
`
`PCV
`
`Sinsusoids AVA
`
`0
`
`0
`
`0
`
`0
`
`0
`
`0 0
`
`0
`
`0 0
`
`0
`
`0
`
`0
`
`0
`
`0
`
`+++
`
`+++
`
`+++
`
`+++
`
`+++
`
`++++
`
`++++
`
`0
`
`0
`
`+
`
`+
`
`0
`
`0
`
`++
`
`++
`
`+
`
`+
`
`+++
`
`+++
`
`+
`
`+
`
`++
`++
`0
`++
`+++
`++
`++
`+/-
`++
`+
`α2c
`Presence of silver granules in cells resulting from in situ hybridization of αAR subtype mRNA probes scored by two independent observ-
`ers. αAR = alpha-adrenergic receptor. Scoring: 0 = silver grain density similar to surrounding background tissue; +/- = very low density of
`silver grains in darkfield; + = silver grains seen only in darkfield; ++ = moderate density in darkfield, some silver grain apparent with bright-
`field; +++ = high density in darkfield, groups of silver grains seen in brightfield; ++++ = very high density silver grains in brightfield. GC =
`goblet cells, CC = ciliated cells, BC = basal cells, SD = serous ducts, MD = mucous ducts, SG = serous glands, MG = mucous glands, PCV
`= post-capillary venules, AVA = arteriovenous anastamosis.
`
`individual subtype location tends to be restricted
`to specific cell types (Table II). Representative light
`and dark field images of nasal turbinate epithelium
`are presented in Figure 2. In non-vascular tissue, the
`overall predominant αAR subtype mRNA is the α1d;
`this subtype is present in epithelium, ducts and glands.
`Less generalized presence of other α1 mRNAs occurs
`in specific cell types such as goblet cells and mucous
`glands (α1a) and ciliated cells, serous ducts and glands,
`and mucous glands (α1b). Within the α2AR family, the
`α2c is present in all epithelial cells, ducts, and glands.
`In addition, α2cARs are present in sinusoids and arte-
`riovenous anastamoses, where it is the only αAR pres-
`ent. In contrast, α2a and α2b signal is more restricted.
`
`Discussion
`In this study we describe, for the first time, αAR
`mRNA subtype distribution in ten cell types present
`in human nasal mucosa. By demonstrating cell and
`subtype specific expression using in situ hybridiza-
`tion, we confirm the hypothesis that αAR subtype
`distribution in the nasal mucosa is heterogenous. Such
`findings provide new mechanistic insight regarding
`potential roles of individual αAR subtypes in human
`nasal mucosa and suggest more selective targets for
`nasal decongestion therapy.
`In spite of the importance of nasal tissue as a phar-
`macologic target, little information is available regard-
`ing αAR distribution in this tissue. For many years
`investigators have assumed beneficial effects of αAR
`
`CAN J ANESTH 54: 7 www.cja-jca.org July, 2007
`
`agonists on nasal tissues resulted from vasoconstric-
`tor effects, essentially dampening fluid flow through
`this tissue. 2–4 Indeed, nasal mucosa is highly vascular.
`Nasal vessels include arteries and arterioles (resistance
`vessels), arteriovenous connections, subepithelial and
`periglandular capillary networks which drain into col-
`lecting veins and venous sinusoids (capacitance ves-
`sels), and finally the sphenopalatine vein.15,16
`Initially investigating αAR effects on vascular tone,
`Ichimura et al.17 demonstrated the presence of post-
`synaptic α1ARs as well as pre- and postsynaptic α2ARs
`in canine nasal vascular smooth muscles using phar-
`macologic approaches. These findings suggested that
`stimulation of either α1 or α2ARs would be expected
`to provide vascular smooth muscle contraction. Using
`guinea pig nasal mucosa, Tanimitsu et al.18 suggested
`that activation of α1aARs result in contraction of nasal
`mucosa vasculature. This is in contrast to pharmaco-
`logic studies in dogs suggesting both α1 and α2AR
`mediate vasoconstriction.19 This disparity between
`guinea pig and dog in nasal turbinate αAR distribution
`is not surprising, given the marked species variability
`in overall expression of AR subtypes, and highlights
`the importance of studies using human tissue.
`Studies in humans suggest the primary mecha-
`nism underlying nasal decongestion appears to be
`venous constriction of the collecting veins and sinu-
`soids;15,16,20–23 such constriction decreases engorge-
`ment of nasal mucosa, attenuating alterations in
`nasal anatomy that have been shown to alter nasal
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`553
`
`In addition to sinusoidal constriction as the main
`mechanism for decongestant action, other mechanisms
`have been shown to contribute to a lesser extent; such
`decongestant targets include α1AR-mediated arterio-
`lar constriction.15,20,30 Andersson and Bende2 studied
`specific αAR effects using topical application of αAR
`agonists and measurement of Xenon washout in the
`nasal mucosa of 43 healthy subjects. Findings from
`this study prompted the authors to conclude that
`vasoconstrictor actions of phenylephrine are likely due
`to preferential action on α1ARs whereas oxymetazo-
`line action is due to α2AR activation.
`While vasoconstriction is thought to be the major
`effect of topical αAR agonists,3 other functional tar-
`gets are possible. For example, α1AR-mediated slow-
`ing of nasal ciliary beat frequency,31 as well as effects
`on mucosal gland functioning,32 provides two alterna-
`tive targets. Alpha AR agonists have been shown to
`decrease the secretion of serous cell products from
`human nasal mucosa although underlying mechanisms
`currently remain unknown.2,4 The strong presence of
`α1d mRNA in epithelial cells, serous, and mucous cells
`of glands and ducts suggests this adrenergic receptor
`subtype may play a role in nasal secretions from these
`cells. Supporting this contention, α1AR antagonists
`(often administered to treat prostate disease) tend to
`increase nasal secretions.33 Since the α1a/d selective
`antagonist tamsulosin also has this effect, this limits
`the possible subtypes involved to the α1a or α1d. Our
`demonstration that only α1d mRNA is present on epi-
`thelium, ducts, and glands strongly suggests that the
`α1dAR subtype is important in nasal secretion. This
`pathway of exocytosis represents a secondary mecha-
`nism (beyond simple vasoconstriction) for the efficacy
`of non-subtype selective α1AR agonists currently being
`marketed as nasal sprays and oral therapies. However,
`since rhinnorhea is a common side-effect of overuse
`of oxymetazoline nose sprays, one might hypothesize
`that avoiding α1dAR effects might minimize this pos-
`sible complication.
`In spite of our novel findings, some limitations
`to our study exist. Because 10 µm thick nasal turbi-
`nate slices cut through multiple cell layers, precise
`determination of exact amounts of tissue mRNA was
`precluded. Instead, we relied on two blinded expert
`observers; while there was excellent concordance
`between observers, it should be remembered that our
`findings represent relative, and not absolute, quantita-
`tion. Another possible limitation is that nasal turbinate
`explants came from patients undergoing functional
`endoscopic surgery, a surgery often employed for
`chronic sinusitis. These patients may have been taking
`medications that may have altered levels of receptor
`
`FIGURE 2 Representative examples of in situ hybridiza-
`tion experiments in human nasal turbinate tissue. The
`α1d-antisense probe demonstrates a high density signal by
`darkfield (A, whitish silver grains in glands, ducts, and
`epithelial cells) and lightfield (B, black grains) microscopy.
`High density signal is absent in equivalent experiments in
`adjacent tissue sections (C and D, respectively) using the
`α1d-sense (control) probe. Similar experiments using α2c-
`antisense probe demonstrate more moderate density signal
`by darkfield (E) and lightfield (F, light brown) micros-
`copy, which is absent in equivalent experiments (G and H,
`respectively) using the α2c-sense (control) probe. Cell type
`specificity in α1 and α2 signalling is evident in epithelial,
`duct and glandular regions, and is also visible in vascular
`tissues at higher levels of magnification (see Table II).
`
`air flow.22,24,25 Our results are the first to address this
`question in humans at an αAR subtype level, revealing
`presence of only α2cAR mRNA in human nasal sinu-
`soids and arteriovenous anastamoses. In the αAR fam-
`ily, α2ARs are primarily responsible for venous (rather
`than arterial) constriction. This is true for a wide range
`of venous capacitance beds such as saphenous vein,26–
`28 dermal veins,28,29 and nasal mucosa.15,16,20,21,30 Our
`findings suggest an important and unique role for the
`α2c subtype in nasal sinusoids, making this receptor a
`new subtype selective target for decongestion.
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`expression and cellular distribution. Countering this
`possibility are previous studies suggesting no major
`changes occur in expression of nasal turbinate αARs
`(α1 vs α2) with chronic sinusitis.7 Obtaining fresh
`human nasal tissue from individuals without disease
`is ethically challenging, making the optimal control
`study almost impossible. Further, it should be remem-
`bered that decongestants are most often utilized by
`individuals with diseased nasal mucosa; therefore, our
`findings are important for the target patient popula-
`tion in any case. Finally, because of lack of monoclonal
`and/or highly specific polyclonal antibodies against
`specific αARs, we cannot be entirely sure the pres-
`ence of mRNA correlates with the presence of recep-
`tor protein at the cell surface. However some of our
`key findings suggest the presence of only one (with
`demonstrated absence of the other five αAR subtypes)
`αAR mRNA species. In these cases, general supportive
`pharmacologic data (α1 vs α2) exist, suggesting the
`mRNA is expressed at a protein level and functional.
`Hence, we have confidence in our major key findings
`that only α2cAR mRNA is noted in nasal sinusoids,
`the precise tissue thought key in decongestant activ-
`ity. Since human tissue samples were quickly frozen
`after explantation and clear αAR subtypes are present
`in each sample (documented by each observer), it is
`highly unlikely that our negative findings for some
`subtypes resulted from RNA degradation. Further
`studies evaluating specific receptor protein expression
`and functional effects (using antibodies and/or more
`highly selective ligands as they become available) will
`be helpful in confirming our findings.
`In summary, this is the first study to report cell
`type-specific distribution of αAR mRNAs. We con-
`firm that α1 and α2AR mRNA is present in human
`nasal turbinate epithelium, ducts, glands, and vessels,
`with selectivity for distinct subtypes limited to spe-
`cific cell types. For instance, α2cAR mRNA is the only
`αAR mRNA present in nasal venous sinusoids. These
`findings suggest that specific α2cAR agonists might
`provide targeted decongestant therapy with fewer
`side-effects.
`
`Acknowledgement
`The authors acknowledge with thanks the editorial
`assistance of Cheryl J. Stetson.
`
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