Functional activation of Gαq/11 protein via α1 -adrenoceptor in rat cerebral cortical membranes.

Although it is recognized that α1 -adrenoceptors are coupled to diverse intracellular signalling pathways, its primary transduction mechanisms are evoked by activating phospholipase C in the cell membrane through Gαq/11 , resulting in production of inositol 1,4,5-trisphosphate and diacylglycerol. However, there have been few studies that indicate directly the involvement of Gαq/11 proteins in this signalling pathway in the central nervous system. In the current study, we tried to pharmacologically characterize (-)-adrenaline-stimulated [35 S]GTPγS binding to Gαq/11 in rat brain membranes. Functional activation of Gαq/11 coupled to α1 -adrenoceptor was investigated by using [35 S]GTPγS binding/immunoprecipitation assay in the membranes prepared from rat cerebral cortex, hippocampus, and striatum. The specific [35 S]GTPγS binding to Gαq/11 was stimulated by (-)-adrenaline in a concentration-dependent and saturable manner in rat cerebral cortical membranes. In hippocampal or striatal membranes, the stimulatory effects of (-)-adrenaline were scarce. The effect of (-)-adrenaline was potently inhibited by prazosin, a potent and selective α1 -adrenoceptor antagonist, but not by yohimbine, a selective α2 -adrenoceptor antagonist. The response was mimicked by cirazoline, but not by R(-)-phenylephrine. Although oxymetazoline also stimulated the specific [35 S]GTPγS binding to Gαq/11 as an apparent "super-agonist", detailed pharmacological characterization revealed that its agonistic properties in this experimental system were derived from off-target effects on 5-HT2A receptors, but not via α1 -adrenoceptors. In conclusion, functional coupling of α1 -adrenoceptors to Gαq/11 proteins are detectable in rat brain membranes by means of [35 S]GTPγS binding/immunoprecipitation assay. It is necessary to interpret the experimental data with caution when oxymetazoline is included as an agonist at α1 -adrenoceptors.

Noradrenaline, oxymetazoline and phorbol myristate acetate induce distinct functional actions and phosphorylation patterns of α1A-adrenergic receptors.

In LNCaP cells that stably express α1A-adrenergic receptors, oxymetazoline increased intracellular calcium and receptor phosphorylation, however, this agonist was a weak partial agonist, as compared to noradrenaline, for calcium signaling. Interestingly, oxymetazoline-induced receptor internalization and desensitization displayed greater effects than those induced by noradrenaline. Phorbol myristate acetate induced modest receptor internalization and minimal desensitization. α1A-Adrenergic receptor interaction with ß-arrestins (colocalization/coimmunoprecipitation) was induced by noradrenaline and oxymetazoline and, to a lesser extent, by phorbol myristate acetate. Oxymetazoline was more potent and effective than noradrenaline in inducing ERK 1/2 phosphorylation. Mass spectrometric analysis of immunopurified α1A-adrenergic receptors from cells treated with adrenergic agonists and the phorbol ester clearly showed that phosphorylated residues were present both at the third intracellular loop and at the carboxyl tail. Distinct phosphorylation patterns were observed under the different conditions. The phosphorylated residues were: a) Baseline and all treatments: T233; b) noradrenaline: S220, S227, S229, S246, S250, S389; c) oxymetazoline: S227, S246, S381, T384, S389; and d) phorbol myristate acetate: S246, S250, S258, S351, S352, S401, S402, S407, T411, S413, T451. Our novel data, describing the α1A-AR phosphorylation sites, suggest that the observed different phosphorylation patterns may participate in defining adrenoceptor localization and action, under the different conditions examined.

Reduction in ultraviolet B light-induced erythema by oxymetazoline and brimonidine is mediated by different α-adrenoceptors.

When applied topically, oxymetazoline and brimonidine reduce the persistent facial erythema of rosacea; this effect is mediated by cutaneous vasoconstriction induced by postsynaptic activation of α-adrenoceptors. We investigated the α-adrenergic pharmacology of oxymetazoline and brimonidine. Functional activity on α-adrenoceptors was evaluated in vitro in HEK293 cells stably expressing single receptor subtypes using a fluorometric imaging plate reader Ca2+ influx assay. Oxymetazoline was an α1 -adrenoceptor agonist with partial α2 -adrenoceptor activity, whereas brimonidine was a highly selective full α2 -adrenoceptor agonist. In vivo pharmacology was investigated in a mouse model of ultraviolet B light (UVB)-induced skin erythema. To selectively inhibit α-adrenoceptor subtypes, mice were injected with prazosin (an α1 -selective antagonist) or rauwolscine (an α2 -selective antagonist) following UVB exposure. Oxymetazoline cream 1.0%, brimonidine gel 0.33% or vehicle control was applied topically, and erythema was measured using a chromameter. Oxymetazoline and brimonidine reduced UVB-induced erythema compared with vehicle control (P < .01). The effect of oxymetazoline was impaired in prazosin-pretreated but not rauwolscine-pretreated mice. Conversely, the effect of brimonidine was impaired in rauwolscine-pretreated but not prazosin-pretreated mice. These data suggest that while oxymetazoline and brimonidine produce cutaneous vasoconstriction, they do so through different α-adrenergic mechanisms, with oxymetazoline primarily acting via α1 -adrenoceptors and brimonidine acting via α2 -adrenoceptors.

Effect of Intranasal Vasoconstrictors on Blood Pressure: A Randomized, Double-Blind, Placebo-Controlled Trial.

BACKGROUND: Treatment for epistaxis includes application of intranasal vasoconstrictors. These medications have a precaution against use in patients with hypertension. Given that many patients who present with epistaxis are hypertensive, these warnings are commonly overridden by clinical necessity. OBJECTIVE: Our aim was to determine the effects of intranasal vasoconstrictors on blood pressure. METHODS: We conducted a single-center, randomized, double-blind, placebo-controlled trial from November 2014 through July 2016. Adult patients being discharged from the emergency department (ED) at Mayo Clinic (Rochester, Minnesota) were recruited. Patients were ineligible if they had a contraindication to study medications, had a history of hypertension, were currently taking antihypertensive or antidysrhythmic medications, or had nasal abnormalities, such as epistaxis. Subjects were randomized to one of four study arms (phenylephrine 0.25%; oxymetazoline 0.05%; lidocaine 1% with epinephrine 1:100,000; or bacteriostatic 0.9% sodium chloride [saline]). Blood pressure and heart rate were measured every 5 min for 30 min. RESULTS: Sixty-eight patients were enrolled in the study; of these, 63 patients completed the study (oxymetazoline, n = 15; phenylephrine, n = 20; lidocaine with epinephrine, n = 11; saline, n = 17). We did not observe any significant differences in mean arterial pressure over time between phenylephrine and saline, oxymetazoline and saline, or lidocaine with epinephrine and saline. The mean greatest increases from baseline in mean arterial pressure, systolic and diastolic blood pressure, and heart rate for each treatment group were also not significantly different from the saline group. CONCLUSIONS: Intranasal vasoconstrictors did not significantly increase blood pressure in patients without a history of hypertension. Our findings reinforce the practice of administering these medications to patients who present to the ED with epistaxis, regardless of high blood pressure.

The Setting Time of Polyether Impression Materials after Contact with Conventional and Experimental Gingival Margin Displacement Agents.

PURPOSE: The compatibility of chemical gingival margin displacement agents with polyether impression materials has not been determined. The aim of this study was to evaluate the setting time of polyether impression elastomers after contact with conventional and experimental gingival displacement agents. MATERIALS AND METHODS: The study compared the setting time of two polyether impression materials: medium body (Impregum Penta Soft) and light body (Impregum Garant L DuoSoft) after contact with 10 gingival displacement agents, including 5 conventional astringents (10%, 20%, and 25% aluminum chloride, 25% aluminum sulfate, and 15.5% ferric sulfate) and 5 experimental adrenergics (0.1% and 0.01% HCl-epinephrine, 0.05% HCl-tetrahydrozoline, 0.05% HCl-oxymetazoline, and 10% HCl-phenylephrine). As many as 120 specimens (60 light body and 60 medium body) were mixed with 20 µl of each of 10 gingival displacement agents, and the time to achieve maximum viscosity was measured with a viscometer. The setting times of these specimens were compared with the control group of 12 specimens, which were polymerized without contact with the displacement agents. The experiments were performed in two environments: 23°C and 37°C (± 0.1°C). Individual and average polymerization time compatibility indices (PTCI) were calculated. Data were analyzed by 2-way ANOVA (α = 0.05). RESULTS: The evaluated chemical displacement agents from both groups changed the setting time of light- and medium-body PE. The negative individual PTCI values achieved astringent (20% aluminum chloride) with two PE in both temperature environments. The average PTCI values of the experimental displacement agents at laboratory and intraoral temperatures were significantly higher than the conventional agents. CONCLUSIONS: The present findings suggest that experimental retraction agents can be recommended clinically as gingival margin displacement agents with minimal effects on the setting time of medium- and light-body polyether impression materials; however, direct contact of chemical displacement agents and polyether impression materials can be avoided.

Evaluating the Effect of Sinex® (0.05% Oxymetazoline) Nasal Spray on Reduction of Nasal Congestion Using Computational Fluid Dynamics.

Computational fluid dynamics (CFD) was used to simulate air flow changes in reconstructed nasal passages based on magnetic resonance imaging (MRI) data from a previous clinical study of 0.05% Oxymetazoline (Vicks Sinex Micromist®). Total-pressure boundary conditions were uniquely applied to accommodate low patency subjects. Net nasal resistance, the primary simulation outcome, was determined using a parallel-circuit analogy and compared across treatments. Relative risk (RR) calculations show that for a 50% reduction in nasal resistance, subjects treated with Sinex® are 9.1 times more likely to achieve this after 8 hr, and 3.2 times more likely after 12 hr compared to Sham.

Differential phosphorylation, desensitization, and internalization of α1A-adrenoceptors activated by norepinephrine and oxymetazoline.

Loss of response on repetitive drug exposure (i.e., tachyphylaxis) is a particular problem for the vasoconstrictor effects of medications containing oxymetazoline (OXY), an α1-adrenoceptor (AR) agonist of the imidazoline class. One cause of tachyphylaxis is receptor desensitization, usually accompanied by phosphorylation and internalization. It is well established that α1A-ARs are less phosphorylated, desensitized, and internalized on exposure to the phenethylamines norepinephrine (NE), epinephrine, or phenylephrine (PE) than are the α1B and α1D subtypes. However, here we show in human embryonic kidney-293 cells that the low-efficacy agonist OXY induces G protein-coupled receptor kinase 2-dependent α1A-AR phosphorylation, followed by rapid desensitization and internalization (∼40% internalization after 5 minutes of stimulation), whereas phosphorylation of α1A-ARs exposed to NE depends to a large extent on protein kinase C activity and is not followed by desensitization, and the receptors undergo delayed internalization (∼35% after 60 minutes of stimulation). Native α1A-ARs from rat tail artery and vas deferens are also desensitized by OXY, but not by NE or PE, indicating that this property of OXY is not limited to recombinant receptors expressed in cell systems. The results of the present study are clearly indicative of agonist-directed α1A-AR regulation. OXY shows functional selectivity relative to NE and PE at α1A-ARs, leading to significant receptor desensitization and internalization, which is important in view of the therapeutic vasoconstrictor effects of this drug and the varied biologic process regulated by α1A-ARs.

The effects of topical oxymetazoline on eyelid position, eye redness, and patient-reported eye appearance: A randomized controlled trial.

PURPOSE: This study assesses the effects of topical oxymetazoline 0.1% on eyelid position, eye redness, and patient-perceived eye appearance in patients without severe ptosis. METHODS: This is a randomized double-blinded controlled trial conducted at a single institute. Patients aged 18-100 years were randomized to receive one drop of oxymetazoline hydrochloride 0.1% or placebo bilaterally. Marginal reflex distance (MRD) 1 and 2, palpebral fissure height, eye redness, and patient-perceived eye appearance were assessed at baseline and two hours after drop instillation. Primary outcome measures included the change in MRD1, MRD2, and palpebral fissure height. Secondary outcome measures included changes in eye redness and patient-perceived eye appearance after drop instillation. RESULTS: In total, 114 patients were included, 57 treatment patients (mean age 36.4 ± 12.7 years, 31.6% male) and 57 controls (mean age 31.3 ± 10.1 years, 33.3% male). Baseline mean MRD1, MRD2, and palpebral fissure were similar between groups (p = 0.24, 0.45, and 0.23, respectively). Changes in MRD1 and eye redness in the treatment group were significantly greater than those in the control group (0.9 ± 0.9 mm vs. - 0.3 ± 0.4 mm, p < 0.001; - 2.6 ± 4.4 vs. - 0.5 ± 2.3, p = 0.002, respectively). Patient-perceived eye appearance was significantly improved in the treatment group compared to the controls (p = 0.002), with more treatment group patients also reporting increased eye size and decreased eye redness (p = 0.008, p = 0.003, respectively). There were 9 treatment-emergent adverse events (TEAEs) in 7 treatment group patients and 5 TEAEs in 5 control patients (p = 0.25), all of which were mild in severity. CONCLUSIONS: Topical oxymetazoline 0.1% increases MRD1 and palpebral fissure height, decreases eye redness, and improves patient-perceived eye appearance.

Naphazoline and oxymetazoline are superior to epinephrine in enhancing the cutaneous analgesia of lidocaine in rats.

This study observed the cutaneous analgesic effect of adrenergic agonists when combined with lidocaine. We aimed at the usefulness of four adrenergic agonists and epinephrine as analgesics or as tools to prolong the effect of local anesthetics using a model of cutaneous trunci muscle reflex (pinprick pain) in rats. We showed that subcutaneous four adrenergic agonists and epinephrine, as well as the local anesthetic bupivacaine and lidocaine, developed a concentration-dependent cutaneous analgesia. The rank order of the efficacy of different compounds (ED50 ; median effective dose) was epinephrine [0.013 (0.012-0.014) µmol] > oxymetazoline [0.25 (0.22-0.28) µmol] > naphazoline [0.42 (0.34-0.53) µmol] = bupivacaine [0.43 (0.37-0.50) µmol] > xylometazoline [1.34 (1.25-1.45) µmol] > lidocaine [5.86 (5.11-6.72) µmol] > tetrahydrozoline [6.76 (6.21-7.36) µmol]. The duration of full recovery caused by tetrahydrozoline, oxymetazoline, or xylometazoline was greater (P < 0.01) than that induced via epinephrine, bupivacaine, lidocaine, or naphazoline at equianesthetic doses (ED25 , ED50 , and ED75 ). Co-administration of lidocaine (ED50 ) with four adrenergic agonists or epinephrine enhanced the cutaneous analgesic effect. We observed that four adrenergic agonists and epinephrine induce analgesia by themselves, and such an effect has a longer duration than local anesthetics. Co-administration of lidocaine with the adrenergic agonist enhances the analgesic effect, and the cutaneous analgesic effect of lidocaine plus naphazoline (or oxymetazoline) is greater than that of lidocaine plus epinephrine.

Novel drug OMS103HP reduces pain and improves joint motion and function for 90 days after arthroscopic meniscectomy.

PURPOSE: This phase 2 study compared OMS103HP (Omeros, Seattle, WA) with control (lactated Ringer's) irrigation solution in patients undergoing arthroscopic partial meniscectomy. METHODS: This was a prospective, multicenter, double-blind, randomized, vehicle-controlled, parallel-group study. Safety and postoperative pain, range of motion, and self-reported function were evaluated for 90 days. Statistical results were based on univariate analysis of variance and repeated-measures analyses. RESULTS: Mean visual analog scale (VAS) pain scores within 24 hours after discharge from the recovery room showed more pain in the control group beginning at 2 hours and peaking at 8 hours. Univariate analysis of variance of mean VAS scores over the 24-hour period did not meet statistical significance. Repeated-measures analysis yielded a statistically significant difference (P = .004) for time-by-treatment interaction, showing a clear drug benefit over time based on VAS scores. There were statistically significant differences at day 7 between the groups in passive flexion without pain (P = .022). The proportion of patients achieving flexion of 95° or greater, 110°, and 125° was greater for the OMS103HP group. The Knee Injury and Osteoarthritis Outcome Score (KOOS) showed statistically significant differences (P ≤ .05) between the OMS103HP and control groups for 4 of 5 outcomes (symptoms, pain, sport and recreation, and knee-based quality of life but not activities of daily living). All scores showed a treatment effect through day 90. The overall incidence of adverse events and abnormal laboratory values for the OMS103HP and control groups was similar. Serious adverse events occurred in 1 control patient. CONCLUSIONS: In this study of patients with meniscal tears who underwent simple debridement, the use of OMS103HP resulted in reduced acute postoperative pain (measured by VAS over the first 24 hours postoperatively), reduced pain during recovery (measured by the KOOS pain subscale, which measures both background levels of pain and exacerbations caused by movements or activities), improved postoperative knee motion, and improved functional outcomes as assessed with the KOOS Knee Survey. Clinical benefits of OMS103HP were consistent and sustained throughout 90 days of postoperative follow-up. LEVEL OF EVIDENCE: Level I, prospective, randomized, controlled trial.

Investigation of Cytotoxic Effects of Oxymetazoline on Lungs in a Rat Model of Rhinitis Medicamentosa.

BACKGROUND: Rhinitis medicamentosa, also known as 'rebound congestion,' is inflammation of the nasal mucosa caused by the overuse of topical nasal decongestants. Although local decongestants resolve the initial nasal obstruction, the overuse causes rebound obstruction. However, how the overuse of the decongestant causes rhinitis medicamentosa is not known. OBJECTIVES: Here, we show the intracellular effects of oxymetazoline, commonly used a local decongestant, on the cell death pathways. We also investigated the antioxidative effects of erdosteine suspension (175 mg/5mL), an antioxidative agent. METHODS: Thirty Wistar-albino rats were used to form the rhinitis medicamentosa model. After rhinitis medicamentosa was clinically detected, we removed the whole lungs of animals to perform the molecular analyses of cell death pathways. RESULTS: We found a statistically significant decrease in the expression levels of Atg5 (p=0.021), Atg7 (p=0.013) and Ulk1 (p=0.036) in the oxymetazoline group compared to the control group (p<0.05); however, Caspase 3 expression level was recorded to be significantly increased in the oxymetazoline group, and the expression level of Beclin1 recorded to be substantially increased in the erdosteine group (p=0.001). CONCLUSION: Based on these grounds, we suggest that vasoconstriction in capillary vessels caused by oxymetazoline could lead to a decrease in the blood supply, which triggers autophagy to ensure cellular homeostasis.

A randomized controlled trial on the effects of oxymetazoline nasal spray after dacryocystorhinostomy among adult patients.

OBJECTIVES: The study aimed to determine the effect of oxymetazoline nasal spray on the patency of the fistula created after dacryocystorhinostomy, specifically: to compare the success of fistula formation with oxymetazoline versus placebo, and to compare the incidence of post-operative congestion, pain and bleeding with oxymetazoline versus placebo. RESULTS: The study was a single-center, randomized controlled, triple-masked study involving the patients of the Plastic-Lacrimal service of a national university hospital. Block randomization was done. Dacryocystorhinostomy was performed by a single-masked surgeon. The intervention group used oxymetazoline. The placebo group used sodium chloride. The data were collected by another masked investigator. The study showed no significant difference in terms of congestion, pain and epistaxis between the two groups at day 2 post-operation. The patency, presence of silicone tube, granuloma formation, and presence of bleeding on both day 2 and day 16 post-operation had no difference between the two groups. This study doesn't support the use of oxymetazoline nasal spray after DCR, since it does not decrease the symptoms of congestion, pain and epistaxis after DCR. Aside from being an additional expense for patients, it also does not affect fistula formation and success rate of the surgery. Trial registration Australian New Zealand Clinical Trial Registry: ACTRN12619001394134, Date registered 10/11/2019, Retrospectively Registered.

Effects of agonists and phorbol esters on α1A-adrenergic receptor-Rab protein interactions.

In a cell line, stably expressing α1A-adrenoceptors fused to the mCherry red fluorescent protein, noradrenaline, methoxamine, and oxymetazoline induced concentration-dependent increases in intracellular calcium. All of these agents increase α1A-adrenoceptor phosphorylation and internalization. Transient co-expression of these receptors with Rab proteins tagged with the enhanced Green Fluorescent Protein was employed to estimate α1A-adrenoceptor-Rab interaction using Förster Resonance Energy Transfer. Noradrenaline and methoxamine increased α1A-adrenoceptor interaction with Rab5 and Rab7 but did not modify it with Rab9. Oxymetazoline induced adrenoceptor interaction with Rab5 and Rab9 and only an insignificant increase in Rab7 signal. Phorbol myristate acetate increased α1A-adrenoceptor interaction with Rab5 and Rab9 but did not modify it with Rab7. The agonists and the active phorbol ester, all of which induce receptor phosphorylation and internalization, favor receptor interaction with Rab5, i.e., association with early endosomes. Cell stimulation with phorbol myristate acetate induced the α1A-adrenoceptors to interact with the late endosomal marker, Rab9, suggesting that the receptors are directed to slow recycling endosomes once they have transited to the Trans-Golgi network to be retrieved to the plasma membrane. The agonists noradrenaline and methoxamine likely induce a faster recycling and might direct some of the adrenoceptors toward degradation and/or very slow recycling to the plasma membrane. Oxymetazoline produced a mixed pattern of interaction with the Rab proteins. These data indicate that α1A-adrenoceptor agonists can trigger different vesicular traffic and receptor fates within the cells.

Regulator of G protein signaling protein suppression of Galphao protein-mediated alpha2A adrenergic receptor inhibition of mouse hippocampal CA3 epileptiform activity.

Activation of G protein-coupled alpha(2) adrenergic receptors (ARs) inhibits epileptiform activity in the hippocampal CA3 region. The specific mechanism underlying this action is unclear. This study investigated which subtype(s) of alpha(2)ARs and G proteins (Galpha(o) or Galpha(i)) are involved in this response using recordings of mouse hippocampal CA3 epileptiform bursts. Application of epinephrine (EPI) or norepinephrine (NE) reduced the frequency of bursts in a concentration-dependent manner: (-)EPI > (-)NE >>> (+)NE. To identify the alpha(2)AR subtype involved, equilibrium dissociation constants (pK(b)) were determined for the selective alphaAR antagonists atipamezole (8.79), rauwolscine (7.75), 2-(2,6-dimethoxyphenoxyethyl)aminomethyl-1,4-benzodioxane hydrochloride (WB-4101; 6.87), and prazosin (5.71). Calculated pK(b) values correlated best with affinities determined previously for the mouse alpha(2A)AR subtype (r = 0.98, slope = 1.07). Furthermore, the inhibitory effects of EPI were lost in hippocampal slices from alpha(2A)AR-but not alpha(2C)AR-knockout mice. Pretreatment with pertussis toxin also reduced the EPI-mediated inhibition of epileptiform bursts. Finally, using knock-in mice with point mutations that disrupt regulator of G protein signaling (RGS) binding to Galpha subunits to enhance signaling by that G protein, the EPI-mediated inhibition of bursts was significantly more potent in slices from RGS-insensitive Galpha(o)(G184S) heterozygous (Galpha(o)+/GS) mice compared with either Galpha(i2)(G184S) heterozygous (Galpha(i2)+/GS) or control mice (EC(50) = 2.5 versus 19 and 23 nM, respectively). Together, these findings indicate that the inhibitory effect of EPI on hippocampal CA3 epileptiform activity uses an alpha(2A)AR/Galpha(o) protein-mediated pathway under strong inhibitory control by RGS proteins. This suggests a possible role for RGS inhibitors or selective alpha(2A)AR agonists as a novel antiepileptic drug therapy.

Dexmedetomidine enhances the local anesthetic action of lidocaine via an alpha-2A adrenoceptor.

BACKGROUND: Clonidine, an alpha-2 adrenoceptor agonist, is a common adjunct in both central and peripheral blocks. Dexmedetomidine, a more selective alpha-2 adrenoceptor agonist, is also known to enhance central neural blockades. Its peripheral effect, however, has not been fully elucidated. Thus, we evaluated the effect of dexmedetomidine and other alpha-2 adrenoceptor agonists on the local anesthetic action of lidocaine at the periphery and explored the mechanism involved. METHODS: alpha-2 Adrenoceptor agonists, including dexmedetomidine, clonidine, and oxymetazoline, combined with lidocaine were intracutaneously injected into the back of male guinea pigs. The test of six pinpricks was applied every 5 min until 60 min after the injection. The number of times which the prick failed to elicit a response during the 60-min period was added and the sum served as an anesthetic score indicating the degree of local anesthesia. Differences from the control value within the group were analyzed using an analysis of variance followed by a post hoc Dunnett's test. Furthermore, we evaluated the antagonism of the effect of dexmedetomidine by yohimbine, an alpha-2A, 2B, and 2C adrenoceptor antagonist, or prazosin, an alpha-1, alpha-2B, and 2C adrenoceptor antagonist, analyzed using a two-way analysis of variance. RESULTS: All alpha-2 adrenoceptor agonists enhanced the degree of local anesthesia of lidocaine in a dose-dependent manner. Furthermore, yohimbine inhibited the effect of dexmedetomidine, whereas prazosin did not. CONCLUSION: We demonstrated that alpha-2 adrenoceptor agonists enhanced the local anesthetic action of lidocaine, and suggest that dexmedetomidine acts via alpha-2A adrenoceptors.

Effect of oxymetazoline on healthy human nasal ciliary beat frequency measured with high-speed digital microscopy and mucociliary transport time.

OBJECTIVES: We investigated the effects of oxymetazoline hydrochloride on the regulation of healthy human nasal ciliary beat frequency (CBF) and its influence on nasal mucociliary transport time (MTT). METHODS: Changes in (cultured) human nasal CBF in response to increasing concentrations of oxymetazoline within 20 minutes were quantified by use of high-speed digital microscopy. Moreover, the MTT before and after application of 0.05% oxymetazoline was determined by use of the saccharin test. RESULTS: Whereas no statistically significant difference was identified when compared to basal CBF at the concentration of 0.025% or 0.05%, both 0.10% and 0.20% oxymetazoline induced a significantly lower CBF at the end of the observation period. The decrement induced by 0.20% oxymetazoline appeared earlier. At concentrations ranging from 0.025% to 0.20%, the inhibitory effect was dependent on the concentration of oxymetazoline. In addition, the use of 0.05% oxymetazoline increased the mean (+/- SD) human nasal MTT from 474 +/- 21 seconds to 572 +/- 41 seconds (n = 29). CONCLUSIONS: The clinical concentration of oxymetazoline, 0.05%, has no obvious inhibitory effect on human nasal CBF in vitro. The increased MTT caused by 0.05% oxymetazoline in vivo is within the normal range.

In Vitro Safety Pharmacology Profiling of Topical α-Adrenergic Agonist Treatments for Erythema of Rosacea.

BACKGROUND: Topical α-adrenergic agonist therapy has been developed to treat the persistent erythema of rosacea patients. Brimonidine and oxymetazoline are both topical α-adrenergic agonists. OBJECTIVES: The objective of this in vitro safety pharmacology study was to compare the potential safety profiles of brimonidine and oxymetazoline. METHODS: Brimonidine and oxymetazoline underwent pharmacological profiling with a standard panel of 151 assays, including α-adrenergic receptors and 5-hydroxytryptamine (5-HT) receptors. A valvular interstitial cell (VIC) proliferation assay was performed with oxymetazoline hydrochloride. RESULTS: Brimonidine was highly selective for the α2 adrenergic receptors, specifically α2A, whereas oxymetazoline was found to be much less selective and was highly active against a wide range of targets. Negligible activity was observed with brimonidine at the 5-HT2B receptor, whereas oxymetazoline had significant 5-HT2B receptor agonist activity and caused proliferation of mitral VICs in vitro. CONCLUSION: As the 5-HT2B receptor is potentially involved in drug-induced valvulopathy, the benefit/risk ratio should be carefully considered, especially in patients with cardiovascular disease or other comorbidities.

Involvement of the autonomic nervous system in the in vivo memory to glucose of pancreatic beta cell in rats.

The fact that the potentiating effect of prolonged hyperglycemia on the subsequent insulin secretion is observed in vivo but not in vitro suggests the involvement of extrapancreatic factors in the in vivo memory of pancreatic beta cells to glucose. We have investigated the possible role of the autonomic nervous system. Rats were made hyperglycemic by a 48-h infusion with glucose (HG rats). At the end of glucose infusion as well as 6 h postinfusion, both parasympathetic and sympathetic nerve activities were profoundly altered: parasympathetic and sympathetic activities, assessed by the firing rate either of the thoracic vagus nerve or the superior cervical ganglion, were dramatically increased and decreased, respectively. Moreover, 6 h after the end of glucose infusion, insulin secretion in response to a glucose load was dramatically increased in HG rats compared to controls. To determine whether these changes could be responsible for the increased sensitivity of the beta cell to glucose, insulin release in response to glucose was measured in HG and control rats, either under subdiaphragmatic vagotomy or after administration of the alpha 2A-adrenergic agonist oxymetazoline. Both treatments partially abolished the hyperresponsiveness of the beta cell to glucose in HG rats. Therefore chronic hyperglycemia brings about changes in the activity of the autonomic nervous system, which in turn are responsible, at least in part, for the generation of enhanced beta cell responsiveness to glucose in vivo.

Pre- and postsynaptic mechanisms in the clonidine- and oxymetazoline-induced inhibition of gastric motility in the rat.

The inhibitory effect of clonidine (non-selective alpha2-adrenoceptor agonist) and oxymetazoline (alpha2A-adrenoceptor selective agonist) was compared on basal and stimulated gastric motor activity (gastric tone and contractions) using the balloon method in the rat. It was shown that oxymetazoline (0.2-1.7 micromol/kg, i.v.) decreased the basal motility, while clonidine (1.9-3.8 micromol/kg, i.v.) failed to affect it. When motility was stimulated centrally by insulin (5 IU/rat, i.v.), both clonidine (1.9-3.8 micromol/kg, i.v.) and oxymetazoline (0.1-3.4 micromol/kg, i.v.) inhibited the gastric motor activity. However, while the effect of clonidine was antagonized by the non-selective alpha2-adrenoceptor antagonist yohimbine (5 micromol/kg, i.v.) and the alpha2A-adrenoceptor selective antagonist BRL 44408 (3 micromol/kg, i.v.), the effect of oxymetazoline was only partially affected. Prazosin (alpha1- and alpha2B-adrenoceptor antagonist, 0.07-0.28 micromol/kg, i.v.) also failed to reverse the effect of oxymetazoline. Furthermore, when gastric motility was stimulated peripherally by activation of postsynaptic cholinergic muscarinic receptors by the combination of carbachol (0.14 micromol/kg, i.v.) and hexamethonium (37 micromol/kg, i.v.), clonidine (3.8 micromol/kg, i.v.) failed to affect the increased motor activity, however, oxymetazoline (0.8-3.4 micromol/kg, i.v.) exerted a pronounced inhibition. These results suggest that different mechanisms may be involved in the inhibitory effect of clonidine and oxymetazoline; while clonidine reduces the gastric motility by activation of presynaptic alpha2-adrenoceptors, postsynaptic component in the effect of oxymetazoline has also been raised.

alpha1-Adrenoceptors in proximal segments of tail arteries from control and reserpinised rats.

It has been recently shown that the supersensitivity of distal segments of the rat tail artery to phenylephrine after chemical sympathectomy with reserpine results from the appearance of alpha(1D)-adrenoceptors. It is known that both alpha(1A)- and alpha(1D)-adrenoceptors are involved in the contractions of proximal portions of the rat tail artery. Therefore, this study investigated whether sympathectomy with reserpine would induce supersensitivity in proximal segments of the rat tail artery, a tissue in which alpha(1D)-adrenoceptors are already functional. Proximal segments of tail arteries from reserpinised rats were three- to sixfold more sensitive to phenylephrine and methoxamine than were arteries from control rats (n = 6-2; p < 0.05). The imidazolines N-[5-(4,5-Dihydro-1H-imidazol-2-yl)-2-hydroxy-5,6,7,8-tetrahydronaphthalen-1-yl]methanesulfonamide hydrobromide (A-61603) and oxymetazoline, which activate selectively alpha(1A)-adrenoceptors, were equipotent in tail arteries from control and reserpinised rats (n = 4-2; p < 0.05), whereas buspirone, which activates selectively alpha(1D)-adrenoceptor, was approximately 4-fold more potent in tail arteries from reserpinised rats (n = 4-6; p < 0.05). Prazosin (nonselective) and 5-methylurapidil (alpha(1A)-selective), were competitive antagonists of contractions induced by phenylephrine and were equipotent in tail arteries from control and reserpinised rats (n = 4-6). The selective alpha(1D)-adrenoceptor antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione dihydrochloride (BMY-7378) presented similar complex antagonism in tail arteries from control and reserpinised rats, with Schild slopes much lower than 1.0 (p < 0.05, n = 4-6). Semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR) revealed that mRNA encoding alpha(1A)-and alpha(1B)-adrenoceptors are similarly distributed in tail arteries from control and reserpinised rats, whereas mRNA for alpha(1D)-adrenoceptors is twice more abundant in the tail artery from reserpinised rats. In conclusion, the supersensitivity induced by reserpine is related only to alpha(1D)-adrenoceptors, even in tissues where this receptor subtype is already present and functional. Only the use of subtype-selective alpha(1)-adrenoceptor agonists detected the increased alpha(1D)-adrenoceptor component after reserpinisation, as the antagonists behaved similarly in tail arteries from control and reserpinised rats.