The effects of certain drugs, cervical sympathetic stimulation and section on nasal patency

The inferior turbinate: An autonomic organ

The inferior turbinate has well-recognized respiratory and immune functions to provide the airway with appropriate warmth, humidification, and filtration of the inspired air while sampling the environment for pathogens. Normal functioning of the inferior turbinate relies on an intact autonomic system to maintain homeostasis within the nasal cavity. The autonomic nervous system innervates the submucosal glands and the vasculature within the inferior turbinate, resulting in control of major turbinate functions: nasal secretions, nasal patency, warmth, and humidification. This review will summarize the autonomic innervations of the turbinates, both the normal and abnormal autonomic processes that contribute to the turbinate functions, and the clinical considerations regarding optimal functioning of the turbinate autonomic system.

Pharmacological Characterization of Postjunctional α-Adrenoceptors in Human Nasal Mucosa

Background

Functional α1- and α2-adrenoreceptor subtype pharmacology was characterized in an in vitro human nasal mucosa contractile bioassay.

Methods

Nasal mucosa was obtained from 49 donor patients and mucosal strips were placed in chambers filled with Krebs–Ringer solution and attached to isometric force transducers.

Results

Nonselective α-adrenoreceptor agonists epinephrine, norepinephrine, and oxymetazoline produced concentration-dependent contractions of isolated human nasal mucosa (pD2= 5.2, 4.9, and 6.5, respectively). The α2-adrenoreceptor agonist BHT-920 (10 μM)–induced contractions were blocked by yohimbine (0.01–1 μM) and prazosin (0.01–1 μM) inhibited the contractile response to the α1-adrenoreceptor agonist phenylephrine (10 μM). Histological analysis showed that phenylephrine and BHT-920 differentially contracted the arteries and veins of human nasal mucosa, respectively.

Conclusion

Our results indicate that functional α1- and α2-adrenoceptors are present and functional in human nasal mucosa. The a 2-adrenoceptors display a predominant role in contracting the veins and the α1-adrenoceptors appear to preferentially constrict the human nasal arteries.

Acoustic Rhinometry in the Dog: A Novel Large Animal Model for Studies of Nasal Congestion

The aim of this project was to develop and pharmacologically characterize an experimental dog model of nasal congestion in which nasal patency is measured using acoustic rhinometry. Solubilized compound 48/80 (0.3–3.0%) was administered intranasally to thiopental anesthetized beagle dogs to elicit nasal congestion via localized mast cell degranulation. Compound 48/80–induced effects on parameters of nasal patency were studied in vehicle-treated animals, as well as in the same animals pretreated 2 hours earlier with oral d-pseudoephedrine or chlorpheniramine. Local mast cell degranulation caused a dose-related decrease in nasal cavity volume and minimal cross-sectional area (Am in) together with a highly variable increase in nasal secretions. Maximal responses were seen at 90–120 minutes after 48/80 administration. Oral administration of the adrenergic agonist, d-pseudoephedrine (3.0 mg/kg), significantly antagonized all of the nasal effects of compound 48/80 (3.0%). In contrast, oral administration of the histamine H1 receptor antagonist chlorpheniramine (10 mg/kg) appeared to reduce the increased nasal secretions but was without effect on the compound 48/80–induced nasal congestion (i.e., volume and Am in). These results show the effectiveness of using acoustic rhinometry in this anesthetized dog model. The observations that compound 48/80–induced nasal congestion was prevented by d-pseudoephedrine pretreatment, but not by chlorpheniramine, suggest that this noninvasive model system may provide an effective tool with which to study the actions of decongestant drugs in preclinical investigations.

An in Vitro Technique for Testing Nasal Vasodilating Agents

An in vitro method for testing vasoactive drugs on nasal blood vessels is described. Isolated dog nasal mucosa contracts when treated with nasal decongestant or stimulated electrically. Vasodilating drugs inhibit this contraction. Atropine blocks the effects of acetylcholine on this tissue.

Sleep, breathing and the nose

During sleep there is a discrete fall in minute ventilation and an associated increase in upper airway resistance. In normal subjects, the nasal part of the upper airway contributes only little to the elevation of the total resistance, which is mainly the consequence of pharyngeal narrowing. Yet, swelling of the nasal mucosa due to congestion of the submucosal capacitance vessels may significantly affect nasal airflow. In many healthy subjects an alternating pattern of congestion and decongestion of the nasal passages is observed. Some individuals demonstrate congestion of the ipsilateral half of the nasal cavity when lying down on the side. Nasal diseases, including structural anomalies and various forms of rhinitis, tend to increase nasal resistance, which typically impairs breathing via the nasal route in recumbency and during sleep. A role of nasal obstruction in the pathogenesis of sleep-disordered breathing has been implicated by many authors. While it proves difficult to show a relationship between the degree of nasal obstruction and the number of disturbed breathing events, the presence of nasal obstruction will most likely have an impact on the severity of sleep-disordered breathing. Identification of nasal obstruction is important in the diagnostic work-up of patients suffering from snoring and sleep apnea.

Pharmacological characterization of alpha 2-adrenoceptor-mediated responses in pig nasal mucosa

1. Pig nasal mucosal strips were incubated with alpha-adrenoceptor antagonists followed by alpha2-adrenoceptor agonist concentration-response curves. 2. Contractions elicited by the alpha2-adrenoceptor agonists BHT-920 (pD2 = 6.16 +/- 0.07), UK 14,304 (pD2 = 6.89 +/- 0.13) and PGE-6201204 (pD2 = 7.12 +/- 0.21) were blocked by the alpha2-adrenoceptor antagonist yohimbine (0.1 microm). In contrast, the alpha1-adrenoceptor antagonist prazosin (0.03 microm) had no effect on the BHT-920-, UK 14,304- and PGE-6201204-induced contractions, but blocked the contractile response to the alpha(1)-adrenoceptor agonist phenylephrine (pD2 = 5.38 +/- 0.04) and the mixed alpha1- and alpha2-adrenoceptor agonist oxymetazoline (pD(2) = 6.30 +/- 0.22). 3. The alpha2-adrenoceptor antagonist yohimbine (0.01-0.1 microm, pA2 = 8.04), alpha2B/C-adrenoceptor antagonist ARC 239 (10 microm, pK(b) = 6.33 +/- 0.21), alpha2A/C-adrenoceptor antagonist WB 4101 (0.3 microm, pK(b) = 8.01 +/- 0.24), alpha2A-adrenoceptor antagonists BRL44408 (0.1 microm, pK(b) = 6.82 +/- 0.34) and RX 821002 (0.1 microm, pKb = 8.31 +/- 0.35), alpha2C-adrenoceptor antagonists spiroxatrine (1 microm, pKb = 7.32 +/- 0.32), rauwolscine (0.1 microm, pKb = 8.16 +/- 0.14) and HV 723 (0.3 microm, pKb = 7.68 +/- 0.14) inhibited BHT-920-induced contractions in pig nasal mucosa. 4. The present antagonist potencies showed correlations with binding affinity estimates (pKi) obtained for these antagonists at the human recombinant alpha2A- and alpha2C-adrenoceptors (r = 0.78 and 0.83, respectively) and with binding affinity estimates (pKd) obtained in pig native alpha2A- and alpha2C-monoreceptor assays (r = 0.85 and 0.78, respectively). No correlation was observed for the alpha2B-subtype. 5. In conclusion, contractile responses to phenylephrine, BHT-920, UK 14,304, PGE-6201204 and oxymetazoline indicate that alpha1- and alpha2-adrenoceptors are present and mediate vasoconstriction in pig nasal mucosa. Furthermore, correlation analysis comparing antagonist potency in pig nasal mucosa with affinities for human recombinant alpha2-adrenoceptors and native pig alpha2-adrenoceptors suggest that alpha2A- and alpha2C-adrenoceptor subtypes constrict pig nasal mucosa vasculature.

Measurement of nasal patency in anesthetized and conscious dogs

Experiments were undertaken to characterize a noninvasive chronic, model of nasal congestion in which nasal patency is measured using acoustic rhinometry. Compound 48/80 was administered intranasally to elicit nasal congestion in five beagle dogs either by syringe (0.5 ml) in thiopental sodium-anesthetized animals or as a mist (0.25 ml) in the same animals in the conscious state. Effects of mast cell degranulation on nasal cavity volume as well as on minimal cross-sectional area (A(min)) and intranasal distance to A(min) (D(min)) were studied. Compound 48/80 caused a dose-related decrease in nasal cavity volume and A(min) together with a variable increase in D(min). Maximal responses were seen at 90-120 min. Compound 48/80 was less effective in producing nasal congestion in conscious animals, which also had significantly larger basal nasal cavity volumes. These results demonstrate the utility of using acoustic rhinometry to measure parameters of nasal patency in dogs and suggest that this model may prove useful in studies of the actions of decongestant drugs.

Pharmacological characterization of a noninvasive, chronic, experimental dog model of nasal congestion

INTRODUCTION

The present experiments were undertaken to pharmacologically characterize a noninvasive, chronic, experimental dog model of nasal congestion with the overall goal of developing an effective tool for studying the mechanism of action of nasal decongestant drugs.

METHODS

Nasal patency was measured using acoustic rhinometry with chlorpheniramine and d-pseudoephedrine used as test agents. Solubilized compound 48/80 was administered as an intranasal mist to a single naris, to elicit nasal congestion in five conscious beagle dogs. Effects of localized degranulation of mast cells on nasal cavity volume, with and without pretreatment with oral decongestant drugs, were measured before and after compound 48/80 administration. Each series of experiments were repeated with a minimum 2-week rest period between trials.

RESULTS

Compound 48/80 caused a decrease of nasal cavity volume (to about 50% of control). Maximal responses were seen at 90-120 min after 48/80 administration and were of similar magnitude when trials were repeated. Oral administration of the adrenergic agonist, d-pseudoephedrine (3 mg/kg), as well as the histamine H(1) receptor antagonist, chlorpheniramine (10 mg/kg), reduced compound 48/80-induced nasal congestion with the greater effect seen with alpha-adrenoceptor blockade.

DISCUSSION

These results demonstrate the utility of using acoustic rhinometry to measure parameters of nasal patency in the conscious dog, and suggest that this model may provide an effective tool with which to study the actions of decongestant drugs in preclinical investigations using conscious preparations. As this technology is noninvasive, replicate determinations can be made in the same experimental subjects. Both alpha-adrenoceptor agonism and, to a lesser extent, histamine H(1) receptor antagonism appear to block compound 48/80-induced nasal congestion in this model.

Sympathetic control of nasal blood flow in the rat mediated by alpha(1)-adrenoceptors

Experiments were undertaken, using laser-Doppler flowmetry, to determine the nature of adrenoceptors mediating sympathetic nerve evoked nasal vasoconstrictor responses in anesthetized rats. Presence of sympathetic tone was confirmed by a large (330%) increase of nasal blood flow following section of the ipsilateral preganglionic cervical sympathetic nerve. Electrical nerve stimulation produced reproducible, frequency-related nasal vasoconstrictor responses with near maximal response, observed at less than 10 Hz. Evoked nasal vasoconstrictor responses were largely blocked with intravenous treatment with the non-selective alpha-adrenoceptor antagonists, phentolamine (5 mg kg(-1)) and phenoxybenzamine (2 mg kg(-1)), as well as with the selective alpha(1)-adrenoceptor antagonist, prazosin (300 microg kg(-1)). alpha(2)-Adrenoceptor antagonism with rauwolscine (500 microg kg(-1)) potentiated neurally evoked nasal vasoconstriction. Neither atropine (1 mg kg(-1)) nor propranolol (1 mg kg(-1)) altered the evoked responses. Rats with intact cervical sympathetic nerves responded to rauwolscine with a modest constriction. Subsequent prazosin administration produced an increase of nasal blood flow of approximately 275%. These results suggest that the nasal vasculature of the rat is under intense sympathetic tone and that the resulting neurogenic vasoconstriction is mediated exclusively by activation of alpha(1)-adrenoceptors.

Studies of spontaneous fluctuations in congestion and nasal mucosal microcirculation and the effects of oxymetazoline using rhinostereometry and micromanipulator guided laser Doppler flowmetry

The mucosa of the inferior turbinate was studied using rhinostereometry and micromanipulator-guided laser Doppler flowmetry in 10 healthy volunteers. First, spontaneous fluctuations were studied measuring congestion and multiple microcirculatory parameters simultaneously every 2 minutes. The subjects were then challenged with oxymetazoline using the same measuring technique studying the effects of the challenge during 12 minutes. There were spontaneous variations in congestion of up to 2.1 mm and variations in perfusion from 38% to 175% of average. There was no correlation between congestion in itself, or change in congestion, to perfusion or any other microcirculatory parameter. After challenge with oxymetazoline there was a rapid decrease in perfusion at 3 minutes after which there were no significant changes. The congestion decreased gradually throughout the procedure. Because congestion reflects the filling of the venous sinusoids and the flowmetry the state of the superficial vessels, we conclude that there are spontaneous short-term fluctuations in the sympathetic tone with independent actions on the different vessels. After challenge with a sympathomimetic drug, there was a decrease in both swelling and flow, but not synchronized. The combination of rhinostereometry and micromanipulator-guided laser Doppler flowmetry is a useful tool to study the dynamics of intranasal challenge reactions.

Increased pressure in venous sinusoids during decongestion of rat nasal mucosa induced by adrenergic agonists

The haemodynamic effects of sympathetic agonists causing decongestion of the nasal mucosa have been investigated in rats. Access to mucosa was obtained from the dorsal side through a small cavity drilled in the nasal bone. The pressures in the venous sinusoids and in the interstitial fluid of nasal mucosa were recorded by micropuncture technique. The local red cell flux (LDF) was monitored by laser Doppler flowmetry, and the blood volume in the mucosa was measured by radio-labelled erythrocytes and albumin. In control rats the tissue blood volume was 0.25 +/- 0.03 g (g wet wt)-1. The interstitial fluid pressure (IFP) was 2.4 +/- 0.6 mmHg and the average blood pressure in venous sinusoids (Ps) was 12.8 +/- 2.7 mmHg. After topical application of noradrenaline (NA) the local blood volume was reduced to 0.12 +/- 0.03 g g-1. Ps was increased to 18.0 +/- 4.0 mmHg, whereas IFP was maintained and LDF was reduced to 40.4% of control, indicating a greater rise in post than in presinusoid vascular resistance. Blocking of both alpha 1 and alpha 2-receptors by phentolamine caused a rise in mucosa blood volume and in LDF by 16 and 20% of control, respectively. Ps increased significantly to 15.2 +/- 3.3 mmHg. Specific stimulation or blocking of alpha 1-receptors by phenylephrine or prazosin induced similar or slightly smaller vascular responses than NA or phentolamine. The effects of the specific alpha 2-agonist (clonidine) or antagonist (yohimbine) on rat mucosa were small, indicating a domination of the alpha 1-receptors. Thus, application of NA caused a rise in blood pressure in the venous sinusoids of nasal mucosa. As LDF fell simultaneously, the reduced blood volume must be due to an increased tone in the muscular wall of venous sinusoids.

Selective brain cooling after bilateral superior cervical sympathectomy in sheep (Ovis aries)

We have investigated the role of the sympathetic innervation of the vasculature of the head in the control of selective brain cooling of sheep, during exposure to high and low ambient temperatures and during endotoxin-induced fever. Bilateral removal of the superior cervical ganglia resulted in a significant reduction of hypothalamic temperature during all procedures. Respiratory rate was also depressed by the sympathectomy, apparently mainly as a result of a decrease in nasal airway patency. Rectal temperature changes after sympathectomy were dependent on the experimental conditions, and the rectal - hypothalamic temperature difference was enhanced during heat exposure and fever. Our results support the contention that sympathetically mediated changes in nasal blood flow and in venous return from the nasal cavity, via the angularis oculi and facial veins, may be involved in the control of selective brain cooling in sheep.

Autonomic nervous control of nasal vasculature and airflow resistance in the anaesthetized dog

1. In pentobarbitone-anaesthetized dogs with constant-flow vascular perfusion of nasal mucosa on both sides, nasal airway resistance, vascular resistance, vascular capacitance (via changes in total venous outflow) and blood flow in the anterior and posterior venous systems were measured. 2. Electrical stimulation of the cut peripheral ends of the cervical sympathetic trunk, caudal nasal nerve, or major palatine nerve increased vascular resistance and decreased vascular capacitance and airway resistance. Propranolol and atropine had no effect on the responses while bretylium completely abolished them; phentolamine greatly lessened the vascular resistance response and partially decreased the vascular capacitance and airway responses. Hence, sympathetic stimulation causes constriction of the resistance vessels via alpha-adrenergic mechanism and constriction of capacitance vessels via alpha-adrenergic as well as some non-adrenergic and non-cholinergic mechanisms. 3. Denervation of the cervical sympathetic trunk, caudal nasal nerve and major palatine nerve decreased nasal vascular resistance and increased vascular capacitance and airway resistance, suggesting tonic sympathetic discharge to nasal mucosa via caudal nasal and major palatine nerves. 4. Electrical stimulation of the nerve of pterygoid canal decreased vascular resistance but increased vascular capacitance (in the posterior venous system) and airway resistance to low-voltage stimulation (below 10 V), and decreased vascular capacitance (in the anterior venous system) and airway resistance to high-voltage stimulation (above 10 V). Hexamethonium reversed the vascular resistance response as well as vascular capacitance and airway responses to high-voltage stimulation. Bretylium and phentolamine enhanced the vascular resistance response and reversed vascular capacitance and airway resistance responses to high-voltage stimulation. Hence, low-voltage stimulation results in parasympathetic dilatation of resistance and capacitance vessels whereas high-voltage stimulation results in parasympathetic dilatation of resistance vessels and sympathetic constriction of capacitance vessels. The parasympathetic vasodilatation was atropine resistance and the sympathetic vasoconstriction was partially via alpha-adrenergic mechanisms. 5. Denervation of the nerve of pterygoid canal did not affect vascular resistance, vascular capacitance or airway resistance suggesting negligible tonic parasympathetic and sympathetic discharges to nasal blood vessels via the nerve. 6. Simultaneous optimal stimulation of sympathetic and parasympathetic nerves resulted in vasoconstriction, especially in capacitance vessels, suggesting sympathetic predominance over parasympathetic control.

Adrenergic and neuropeptide Y supersensitivity in denervated nasal mucosa vasculature of the pig

The effects of sympathetic denervation for 2 weeks on vasoconstrictor reactivity to alpha-adrenoceptor agonists, neuropeptide Y (NPY) and alpha,beta-methylene adenosine triphosphate (mATP) were investigated in different vascular compartments of the nasal mucosa of pentobarbital-anesthetized pigs. Supersensitivity to the vasoconstrictor actions of noradrenaline (NA) was observed in the function of both resistance vessels (as revealed by a reduction in arterial blood flow) and capacitance vessels (reflected by a reduction in nasal mucosal volume). The NA supersensitivity was, to a large extent, of prejunctional type since inhibition of neuronal uptake by desipramine also markedly enhanced the NA response. Whereas the reduction in arterial blood flow and in mucosal volume induced by the alpha 1-agonist, phenylephrine, was not changed by denervation, the effects of the alpha 2-agonists UK 14.304 and oxymetazoline were enhanced and/or prolonged. Furthermore, the reduction in blood flow and volume induced by NPY was enhanced in both amplitude and duration. The effects of mATP on the amplitude of the volume response and the duration of the blood flow and volume changes were increased. The maximal reduction in superficial blood flow was larger, as revealed by the laser Doppler flowmetry signal, when NPY or adrenoceptor agonists were given to denervated animals. It is concluded that sympathetic denervation is associated with increased sensitivity and prolonged responses to a variety of vasoconstrictor agents in the pig nasal mucosa in vivo. However, alpha 2-adrenoceptor, NPY and mATP mechanisms seem to be influenced more by denervation than by alpha 1-adrenoceptor sensitivity.

Nasal resistance and nasal blood flow in postural changes

Posture greatly influences nasal resistance. To investigate whether nasal blood flow synchronizes with nasal resistance during changes in posture, correlation coefficients were calculated based on findings from both nasal cavities in 14 normal subjects. There was no correlation between nasal resistance and nasal blood flow, except in the left nasal cavity of one subject. Nasal blood flow was measured by a laser Doppler flowmeter, which detects the blood flow in the superficial part of the nasal mucosa. Nasal resistance is regulated mainly by capacitance vessels located in the deeper part of the nasal mucosa. Therefore, the dissociation in nasal resistance and blood flow responses to postural changes noted in our study suggests that vessels in different parts of the nasal mucosa respond differently to this same stimulus.

Evidence for presynaptic parasympathetic receptors on nasal blood vessels

Noradrenergic synapses in the heart and several blood vessels have been shown to possess prejunctional receptors that modulate the release of norepinephrine from the synapse. The present experiment attempted to find evidence for presynaptic receptors for acetylcholine that modulated norepinephrine release. From the evidence obtained, it appears that the acetylcholine released from nasal parasympathetic fibers does not directly affect the smooth muscle of nasal blood vessels. Acetylcholine does, however, appear to inhibit the release of norepinephrine from nasal sympathetic nerve terminals. It appears that any nasal vasodilation produced by nasal parasympathetic fibers is caused by acetylcholine acting on an inhibitory, presynaptic, muscarinic receptor on the sympathetic nerve terminals. Acetylcholine would exert its control over nasal vessels by regulating the degree of sympathetic neurotransmitter release.

Effect of ammonia on nasal resistance in atopic and nonatopic subjects

Nasal airway resistance (NAR) was assessed from the slope of pressure-glow curves obtained during normal nasal breathing. Volunteers were classified as atopic or nonatopic according to strict critera. 100 ppm NH3 was introduced into each nostril for periods ranging from 5 to 30 seconds with frequent NAR monitoring. A progressive increase in NAR responses was obtained with incremental NH3 exposure, but no significant difference was noted between the mean response of atopic and nonatopic subjects. Control exposures to compressed air under the same pressure generally produced only a small change in NAR, while aerosolized buffered saline increased NAR more than compressed air. The nasal response to NH3 was effectively inhibited by intranasal atropine administration but not by chlorpheniramine. The nasal response to NH3 was effectively inhibited by intranasal atropine administration but not by chlorpheniramine. The described procedure provides a safe and simple method for studying semiquantitatively the short-term effects of inhaled irritants on the nose.