Tumour necrosis factor-alpha expression and cell recruitment in Sephadex particle-induced lung inflammation: effects of dexamethasone and cyclosporin A

Preclinical Evaluation of the Effects of Trazpiroben (TAK-906), a Novel, Potent Dopamine D2/D3 Receptor Antagonist for the Management of Gastroparesis

Current therapies for gastroparesis, metoclopramide and domperidone, carry risks of extrapyramidal symptoms and life-threatening cardiac arrhythmias. Trazpiroben, a novel, potent dopamine D₂/D₃ receptor antagonist, has low brain permeation and very low affinity for human ether-à-go-go-related gene (hERG) channel inhibition, potentially improving on safety profiles of existing therapies. Trazpiroben demonstrated the following receptor affinities: high for D₂ and D_3, moderate for D₄ and minimal for D₁ and D₅ It demonstrated moderate affinity for adrenergic alpha 1B (α_1B) and 5-hydroxytryptamine 2A (5HT_2A) receptors and low potential for off-target adverse events (AEs). Trazpiroben potently inhibited dopamine-activated D_2L receptor activation of cognate G-proteins in human embryonic kidney 293 cell membranes and was a neutral D_2L receptor antagonist. In vivo, trazpiroben dose-dependently increased prolactin release in orally dosed rat (0.1-1mg/kg). Additionally, multiple oral doses in the rat (100mg/kg) and dog (50mg/kg) for 3 days produced robust plasma exposures and prolactin increases in both species. Trazpiroben inhibited retching/vomiting in the dog with apomorphine-induced emesis with a potency (0.1-1mg/kg) like that of trazpiroben-mediated prolactin increases in rat. Oral trazpiroben (1, 10, and 30mg/kg) did not affect rat rotarod performance, suggesting low brain penetration. Trazpiroben concentrations were low in cerebrospinal fluid versus plasma following multiple oral doses for 4 days in rat and dog. Trazpiroben weakly inhibited the hERG channel current (concentration causing half-maximal inhibition of control-specific binding of 15.6µM), indicating little potential for disrupting cardiac rhythm. Overall, trazpiroben is a potent D₂/D₃ receptor antagonist designed to avoid serious potential AEs associated with current gastroparesis therapies. Significance Statement Trazpiroben is a novel, potent dopamine D₂/D₃ selective receptor antagonist designed to avoid adverse effects associated with the current pharmacological therapies, metoclopramide and domperidone. Pre-clinical studies have demonstrated low brain penetration and weak affinity for the hERG channel, indicating that trazpiroben is not expected to be associated with central nervous system or cardiovascular safety issues. With these pharmacological properties, trazpiroben may represent a viable new treatment option for gastroparesis due to a potentially improved safety profile relative to existing therapies.

4-thiouridine induces dose-dependent reduction of oedema, leucocyte influx and tumour necrosis factor in lung inflammation

Recent reports demonstrate a role for nucleotides as inflammatory modulators. Uridine, for example, reduces oedema formation and leucocyte infiltration in a Sephadex-induced lung inflammation model. Tumour necrosis factor (TNF) concentration was also reduced. Previous in vivo observations indicated that 4-thiouridine might have similar effects on leucocyte infiltration and TNF release. The aim of this study was thus to investigate the effects of 4-thiouridine in greater detail. We used a Sephadex-induced acute lung inflammation model in Sprague-Dawley rats. The dextran beads were instilled intratracheally into the lungs, which were excised and examined after 24 h. Sephadex alone led to massive oedema formation and infiltration of macrophages, neutrophils and eosinophils. Microgranulomas with giant cell formations were clearly visible around the partially degraded beads. A significant increase in bronchoalveolar lavage fluid (BALF) content of TNF and leukotrienes was also seen. 4-Thiouridine co-administration affected all variables investigated in this model, i.e. oedema, microscopic and macroscopic appearance of lung tissue, total leucocyte and differential leucocyte counts in BALF, TNF and leukotrienes C(4) (LTC(4)), LTD(4 )and LTE(4) in BALF, indicating a reproducible anti-inflammatory effect. In conclusion, we have demonstrated that 4-thiouridine has anti-inflammatory effects similar to those of uridine. To our knowledge, this is the first demonstration of pharmacological 4-thiouridine effects in vivo. The results suggest nucleoside/nucleotide involvement in inflammatory processes, warranting further studies on nucleoside analogues as attractive new alternatives in the treatment of inflammatory diseases.

Facilitatory interplay in alpha 1a and beta 2 adrenoceptor function reveals a non-Gq signaling mode: implications for diversification of intracellular signal transduction

Agonist occupied alpha(1)-adrenoceptors (alpha(1)-ARs) engage several signaling pathways, including phosphatidylinositol hydrolysis, calcium mobilization, arachidonic acid release, mitogen-activated protein (MAP) kinase activation, and cAMP accumulation. The natural agonist norepinephrine (NE) activates with variable affinity and intrinsic efficacy all adrenoceptors, and in cells that coexpress alpha(1)- and beta-AR subtypes, such as cardiomyocytes, this leads to coactivation of multiple downstream pathways. This may result in pathway cross-talk with significant consequences to heart physiology and pathologic state. To dissect signaling components involved specifically in alpha(1A)- and beta(2)-AR signal interplay, we have developed a recombinant model system that mimics the levels of receptor expression observed in native cells. We followed intracellular Ca(2+) mobilization to monitor in real time the activation of both G(q) and G(s) pathways. We found that coactivation of alpha(1A)- and beta(2)-AR by the nonselective agonist NE or via a combination of the highly selective alpha(1A)-AR agonist A61603 and the beta-selective agonist isoproterenol led to increases in Ca(2+) influx from the extracellular compartment relative to stimulation with A61603 alone, with no effect on the associated transient release of Ca(2+) from intracellular stores. This effect became more evident upon examination of an alpha(1A)-AR variant exhibiting a partial defect in coupling to G(q), and we attribute it to potentiation of a non G(q)-pathway, uncovered by application of a combination of xestospongin C, an endoplasmic reticulum inositol 1,4,5-triphosphate receptor blocker, and 2-aminoethoxydiphenyl borate, a nonselective storeoperated Ca(2+) entry channel blocker. We also found that stimulation with A61603 of a second alpha(1A)-AR variant entirely unable to signal induced no Ca(2+) unless beta(2)-AR was concomitantly activated. These results may be accounted for by the presence of alpha(1A)/beta(2)-AR heterodimers or alternatively by specific adrenoceptor signal cross-talk resulting in distinct pharmacological behavior. Finally, our findings provide a new conceptual framework to rationalize outcomes from clinical studies targeting alpha- and beta-adrenoceptors.

P-glycoprotein induction: an antidotal pathway for paraquat-induced lung toxicity

The widespread use of the nonselective contact herbicide paraquat (PQ) has been the cause of thousands of deaths from both accidental and voluntary ingestion. The main target organ for PQ toxicity is the lung. No antidote or effective treatment to decrease PQ accumulation in the lung or to disrupt its toxicity has yet been developed. The present study describes a procedure that leads to a remarkable decrease in PQ accumulation in the lung, together with an increase in its fecal excretion and a subsequent decrease in several biochemical and histopathological biomarkers of toxicity. The administration of dexamethasone (100 mg/kg ip) to Wistar rats, 2 h after PQ intoxication (25 mg/kg ip), decreased the lung PQ accumulation to about 40% of the group exposed to only PQ and led to an improvement in tissue healing in just 24 h as a result of the induction of de novo synthesis of P-glycoprotein (P-gp). The involvement of P-gp in these effects was confirmed by Western blot analysis and by the use of a competitive inhibitor of this transporter, verapamil (10 mg/kg ip), which, given 1 h before dexamethasone, blocked its protective effects, causing instead an increase in lung PQ concentration and an aggravation of toxicity. In conclusion, the induction of P-gp, leading to a decrease in lung levels of PQ and the consequent prevention of toxicity, seems to be a new and promising treatment for PQ poisonings that should be further clinically tested.

α1-Adrenoceptor Subtype Selectivity and Organ Specificity of Silodosin (KMD-3213)

The selectivity of silodosin (KMD-3213), an antagonist of alpha(1)-adrenoceptor (AR), to the subtypes (alpha(1A)-, alpha(1B)- and alpha(1D)-ARs) was examined by a receptor-binding study and a functional pharmacological study, and we compared its subtype-selectivity with those of other alpha(1)-AR antagonists. In the receptor-binding study, a replacement experiment using [(3)H]-prazosin was conducted using the membrane fraction of mouse-derived LM (tk-) cells in which each of three human alpha(1)-AR subtypes was expressed. In the functional pharmacological study, the following isolated tissues were used as representative organs with high distribution densities of alpha(1)-AR subtypes (alpha(1A)-AR: rabbit prostate, urethra and bladder trigone; alpha(1B)-AR: rat spleen; alpha(1D)-AR: rat thoracic aorta). Using the Magnus method, we studied the inhibitory effect of silodosin on noradrenaline-induced contraction, and compared it with those of tamsulosin hydrochloride, naftopidil and prazosin hydrochloride. Silodosin showed higher selectivity for the alpha(1A)-AR subtype than tamsulosin hydrochloride, naftopidil or prazosin hydrochloride (affinity was highest for tamsulosin hydrochloride, followed by silodosin, prazosin hydrochloride and naftopidil in that order). Silodosin strongly antagonized noradrenaline-induced contractions in rabbit lower urinary tract tissues (including prostate, urethra and bladder trigone, with pA(2) or pKb values of 9.60, 8.71 and 9.35, respectively). On the other hand, the pA(2) values for antagonism of noradrenaline-induced contractions in rat isolated spleen and rat isolated thoracic aorta were 7.15 and 7.88, respectively. Selectivity for lower urinary tract was higher for silodosin than for the other alpha(1)-AR antagonists. Our data suggest that silodosin has a high selectivity for the alpha(1A)-AR subtype and for the lower urinary tract.

Effects of uridine, isomatitol and 4-thiouridine on in vitro cell adhesion and in vivo effects of 4-thiouridine in a lung inflammation model

Since leukocyte adhesion to endothelial cells is crucial for extravasation of leukocytes to sites of inflammation, inhibition of cell-cell adhesion has been suggested as a means to achieve selective modulation of the immune system. We have, using a static in vitro adhesion assay involving adhesion of granulocytes to tumor necrosis factor alpha (TNFalpha)-stimulated human umbilical vein endothelial cells (HUVEC), found three substances--uridine, isomaltitol and 4-thiouridine-that, independently and significantly, reduced leukocyte adhesion by approximately 30-65%. 4-Thiouridine was also tested in an in vivo model of Sephadex (SDX)-induced lung inflammation with Sprague-Dawley rats. Intratracheal instillation of Sephadex (5 mg/kg) alone resulted in a dramatic increase in lung edema and total leukocyte count after 24 h. A differential count of bronchoalveolar lavage (BAL) cells indicated an increased influx of macrophages, eosinophils and neutrophils. Co-administration of 4-thiouridine significantly reduced lung edema by 38%. There was also a significant reduction of the total leukocyte count by 58%. The differential leukocyte count indicated that eosinophil influx alone was reduced by 70%. After Sephadex challenge, we found elevated levels of TNFalpha--an important inflammatory mediator--in the bronchoalveolar lavage fluid (BALF). TNFalpha levels were significantly reduced by more than 80% by co-administration of 4-thoiuridine. These results suggest that uridine, isomaltitol and, especially, 4-thiouridine affect adhesion between leukocytes and activated endothelium, and warrant further in vitro and in vivo studies.

High-affinity interactions between human alpha1A-adrenoceptor C-terminal splice variants produce homo- and heterodimers but do not generate the alpha1L-adrenoceptor

Using combinations of bioluminescence resonance energy transfer, time-resolved fluorescence resonance energy transfer and the functional complementation of pairs of inactive receptor-G protein fusion proteins, the human alpha(1A-1)-adrenoceptor was shown to form homodimeric/oligomeric complexes when expressed in human embryonic kidney (HEK) 293 cells. Saturation bioluminescence resonance energy transfer studies indicated the alpha(1A-1)-adrenoceptor homodimer interactions to be high affinity and some 75 times greater than interactions between the alpha(1A-1)-adrenoceptor and the delta opioid peptide receptor. Only a fraction of the alpha(1A-1)-adrenoceptors was at the plasma membrane of HEK293 cells at steady state. However, dimers of alpha(1A-1)-adrenoceptors were also present in intracellular membranes, and the dimer status of those delivered to the cell surface was unaffected by the presence of agonist. Splice variation can generate at least three forms of the human alpha(1A-1)-adrenoceptor with differences limited to the C-terminal tail. Each of the alpha(1A-1), alpha(1A-2a), and alpha(1A-3a)-adrenoceptor splice variants formed homodimers/oligomers, and all combinations of these splice variants were able to generate heterodimeric/oligomeric interactions. Despite the coexpression of these splice variants in human tissues that possess the pharmacologically defined alpha(1L)-adrenoceptor binding site, coexpression of any pair in HEK293 cells failed to generate ligand binding characteristic of the alpha(1L)-adrenoceptor.

Identification of α-1L Adrenoceptor in Rabbit Ear Artery

The alpha-1L adrenoceptor (AR) was identified in rabbit ear artery by both functional and ligand binding studies. In functional studies using arterial rings, the contractile response to NS-49 [(R)-(-)-3'-(2-amino-1-hydroxyethyl)-4'-fluorometh-anesulfonanilide hydrochloride] (alpha-1A and alpha-1L AR-selective agonist) was competitively antagonized with low affinities by prazosin, RS-17053 [N-[2-(2-cyclopropylmethoxyphenoxy) ethyl]-5-chloro-alpha,alpha-dimethyl-1H-indole-3-ethamine hydrochloride], and 5-methylurapidil but with high affinities by tamsulosin and KMD-3213 [(-)-1-(3-hydroxypropyl)-5-[(2R)-2-([2-[(2,2,2-trifluoroethoxy)phenoxy]ethyl]amino)propyl]-2,3-dihydro-1H-indole-7-carboxamide]. In contrast, the response to noradrenaline (nonselective alpha-1 AR agonist) was inhibited noncompetitively by these antagonists (except 5-methylurapidil) with Schild slopes different from unity. These results suggest that the response to NS-49 was mediated predominantly via alpha-1L ARs, whereas the response to noradrenaline was produced through two distinct alpha-1 AR subtypes (presumably alpha-1B and alpha-1L ARs). In binding studies with intact segments of rabbit ear artery, [3H]KMD-3213 bound with high affinity (pKD=9.7) to alpha-1 ARs, which were subdivided by prazosin, RS-17053, and 5-methylurapidil into two subtypes (alpha-1A and alpha-1L ARs). In contrast, [3H]prazosin binding sites in ear artery segments (pKD = 9.8) were identified as alpha-1A and alpha-1B ARs. In conventional binding studies using isolated rabbit ear artery microsomal membranes, [3H]KMD-3213 binding sites were identified as alpha-1A ARs with high affinities for prazosin, RS-17053, and 5-methylurapidil. Our study indicates that an alpha-1L AR having a unique pharmacological profile coexists with alpha-1A and alpha-1B ARs in rabbit ear artery and can be identified either functionally or by binding studies using intact tissues but not microsomal membrane preparations.

Subtype-Specific Dimerization of α1-Adrenoceptors: Effects on Receptor Expression and Pharmacological Properties

The potential role of dimerization in controlling the expression and pharmacological properties of alpha1-adrenoceptor subtypes was examined using coimmunoprecipitation of epitope-tagged receptors. Human alpha1-adrenoceptor subtypes (alpha1A, alpha1B, alpha1D) were tagged at their amino-termini with Flag or hemagglutinin epitopes and transfected into human embryonic kidney 293 cells. Homodimerization of all three subtypes was observed by coimmunoprecipitation of receptors with different tags and was not altered by norepinephrine treatment. Heterodimer formation between hemagglutinin-tagged alpha1B-adrenoceptors and Flag-tagged alpha1A- or alpha1D-adrenoceptors was also observed. However, no alpha1A/alpha1D-adrenoceptor heterodimers were observed, suggesting that dimerization is subtype-specific. The extent of heterodimerization was also unaltered by norepinephrine treatment. alpha1-Adrenoceptor truncation mutants lacking carboxyl or amino-terminal sequences formed homo- and heterodimers similarly to full-length receptors, suggesting that these domains play little or no role in dimerization. Biotinylation with a membrane-impermeable agent showed that monomers and homo- and hetero-oligomers of all three subtypes are expressed on the cell surface. Radioligand binding studies showed that heterodimerization did not alter the affinity of alpha1-adrenoceptors for norepinephrine, prazosin, or subtype-selective antagonists, suggesting that dimerization does not result in pharmacologically distinct subtypes. However, coexpression of alpha1B-adrenoceptors significantly increased both binding site density and protein expression of alpha1A- and alpha1D-adrenoceptors, and increased cell surface expression of alpha1D-adrenoceptors, suggesting a functional role for heterodimerization. Conversely, coexpression of alpha1A-with alpha1D-adrenoceptors, which did not heterodimerize, had no effect on receptor density or protein. These studies demonstrate subtype-selective heterodimerization of alpha1-adrenoceptors, which does not change their pharmacological properties but seems to have functional consequences in regulating receptor expression and trafficking.

Methylprednisolone effects on oxygenation and histology in a rat model of acute lung injury

We examined the effects of methylprednisolone on gas exchange, pressure-volume curve, lavage fluid inflammatory cell counts, protein content, surfactant pool size, and lung histology in a rat model of paraquat-induced lung injury. Twenty-three adult male Sprague-Dawley rats received intraperitoneal paraquat injection (35 mg/kg) and were randomly divided into three groups: (1). control group received no further treatment; (2). 1-dose methylprednisolone group received a concomitant intraperitoneal methylprednisolone injection (30 mg/kg); (3). 3-dose methylprednisolone group received a concomitant and daily intraperitoneal methylprednisolone injection (30 mg/kg) for three doses. Three days after paraquat injection, the rat was ventilated for 90 min, a static pressure-volume curve and bronchoalveolar lavage was performed, and postmortem histology was examined. Surfactant pool size of the 3-dose methylprednisolone group was significantly increased when compared with the control and 1-dose methylprednisolone groups. Methylprednisolone treatment increased oxygenation and the value was statistically significant for 3-dose methylprednisolone group at 90 min of ventilation. Inflammatory cell counts in bronchoalveolar lavage fluid and lung injury score were decreased as the methylprednisolone dose increased. We conclude that high-dose methylprednisolone treatment increased surfactant pool size and improved lung histology of paraquat-injured lungs but this augmentation could not significantly improve oxygenation throughout the ventilation period.

Dexamethasone reduces lung eosinophilia, and VCAM-1 and ICAM-1 expression induced by Sephadex beads in rats

Airway eosinophilia is one of the key pathophysiologic features in asthma. The endothelial adhesion molecules, vascular cell adhesion molecule (VCAM-1) and intercellular adhesion molecule (ICAM-1), have previously been shown to play a crucial role in eosinophil recruitment into the inflamed airway. We have investigated the effects of dexamethasone on eosinophilia into the bronchoalveolar lavage fluid, and the upregulation of VCAM-1 and ICAM-1 expression, measured by immunoblotting, induced by i.v. injection of Sephadex beads into rats. The beads significantly increased the lung eosinophilia, and expression of VCAM-1 and ICAM-1 in the lung. Pretreatment with dexamethasone (0.1 to 2 mg/kg i.p.) strongly inhibited all the airway inflammatory events in a dose-dependent manner. In conclusion, glucocorticoids may be potent inhibitors of lung eosinophilia, at least in part, due to the prevention of the upregulation of VCAM-1 and ICAM-1 expression.

Tonic inhibitory role for cAMP in alpha(1a)-adrenergic receptor coupling to extracellular signal-regulated kinases 1/2

alpha(1a)-Adrenergic receptors (ARs) couple to phosphoinositide hydrolysis, adenylyl cyclase, and mitogen-activated protein kinase (MAPK) pathways. However, the interaction among these signaling pathways in activating extracellular signal-regulated kinase 1/2 (ERK1/2) is not well understood. We investigated the coupling of alpha(1a)-ARs to ERK1/2 in Chinese hamster ovary (CHO)-K1 cells stably transfected with mouse alpha(1a)-ARs, as well as the interaction between ERK1/2 and norepinephrine-induced cAMP accumulation. alpha(1a)-AR activation by norepinephrine increased the cytosolic Ca(2+) concentration and phosphorylated ERK1/2 in a time- and concentration-dependent manner. ERK1/2 phosphorylation was blocked by the MAPK kinase 1/2 inhibitor 2'-amino-3'-methoxyflavone (PD 98059) and the alpha(1)-AR antagonist prazosin. A transient elevation in intracellular Ca(2+) was required for the phosphorylation of ERK1/2; however, activation of protein kinase C did not seem to be required for ERK1/2 phosphorylation. Norepinephrine also stimulated cAMP accumulation in transfected CHO-K1 cells in a concentration-dependent manner via alpha(1a)-ARs, which was blocked by the Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid. Norepinephrine-induced ERK1/2 phosphorylation was inhibited by the adenylyl cyclase activator forskolin and was enhanced by the adenylyl cyclase inhibitor 9-(tetrahydro-2-furanyl)-9H-purine-6-amine (SQ 22536) and the protein kinase A inhibitor 4-cyano-3-methylisoquinoline. In conclusion, in transfected CHO-K1 cells, alpha(1a)-AR activation activates both phospholipase C and adenylyl cyclase-mediated signaling pathways. alpha(1a)-AR-mediated ERK1/2 phosphorylation was dependent on a rise in intracellular Ca(2+), and this pathway was reciprocally regulated by the concomitant activation of adenylyl cyclase, which inhibits ERK1/2 phosphorylation. Thus, alpha(1a)-AR stimulation of cAMP production may play an important role in regulating ERK1/2 phosphorylation in cell lines and native tissues.

Preclinical pharmacology of fiduxosin, a novel alpha(1)-adrenoceptor antagonist with uroselective properties

Benign prostatic hyperplasia (BPH), common in aging males, is often treated with alpha(1)-adrenoceptor antagonists. To minimize hypotensive and other side effects, compounds with selective antagonist activity at alpha(1A)- and alpha(1D)- (compared with alpha(1B)-) adrenoceptors were evaluated that would block lower urinary tract alpha(1)-adrenoceptors in preference to cardiovascular alpha(1B)-adrenoceptors. Fiduxosin (3-[4-((3aR,9bR)-cis-9-methoxy-1,2,3,3a,4,9b-hexahydro-[1]-benzopyrano[3,4-c]pyrrol-2-yl)butyl]-8-phenyl-pyrazino[2',3':4,5] thieno-[3,2-d]pyrimidine-2,4(1H,3H)-dione; ABT-980) was tested in radioligand binding assays, isolated tissue bioassays, intraurethral pressure (IUP) tests in isoflurane-anesthetized dogs, and blood pressure analyses in spontaneously hypertensive rats (SHR). Fiduxosin had higher affinity for cloned human alpha(1a)- (0.16 nM) and alpha(1d)-adrenoceptors (0.92 nM) in radioligand binding studies compared with alpha(1b)-adrenoceptors (25 nM) or in isolated tissue bioassays [pA(2) values of 8.5-9.6 for alpha(1A)-receptors in rat vas deferens or canine prostate strips, 8.9 at alpha(1D)-adrenoceptors (rat aorta), compared with 7.1 at alpha(1B)-adrenoceptors (rat spleen)]. Furthermore, the compound antagonized putative alpha(1L)-adrenoceptors in the rabbit urethra (pA(2) value of 7.58). Fiduxosin blocked epinephrine-induced increases in canine IUP (pseudo-pA(2) value of 8.12), eliciting only transient decreases in mean arterial blood pressure (MAP) in SHR. The area under the curve (AUC(0-->60) min) for the hypotensive response was dose related with a log index value for fiduxosin of 5.23, indicating a selectivity of 770-fold comparing IUP to MAP effects. Preferential antagonism of alpha(1A)- and alpha(1D)- versus alpha(1B)-adrenoceptors in vitro, blockade of putative alpha(1L)-sites in vitro, and selective effects on lower urinary tract function versus blood pressure in vivo by fiduxosin suggest the potential utility of this compound for the treatment of BPH.

alpha(1A)-adrenoceptors mediate sympathetically evoked pupillary dilation in rats

Evidence suggests that in some species (cats, rabbits, and possibly humans) alpha-adrenoceptors in the iris dilator muscle are "atypical" in that they cannot be readily classified by conventional criteria. This study was undertaken in an attempt to characterize the alpha-adrenoceptor subtype(s) mediating sympathetically elicited mydriasis in rats. Frequency-response pupillary dilator curves were generated by stimulation of the preganglionic cervical sympathetic nerve (1-32 Hz) in pentobarbital-anesthetized rats. Evoked responses were inhibited by systemic administration of nonselective alpha-adrenergic antagonists, phentolamine (0.3-10 mg/kg) and phenoxybenzamine (0.03-1 mg/kg). The selective alpha(1)-adrenergic antagonist, prazosin (0.01-1 mg/kg), also was effective, although alpha(2)-adrenergic antagonism with rauwolscine (0.1-1 mg/kg) was not. alpha(1A)-Adrenoceptor-selective antagonists, 2-([2,6-dimethoxyphenoxyethyl]aminomethyl)-1,4-benzodioxane (WB-4101; 0.1-1 mg/kg) and 5-methylurapidil (0.1-1 mg/kg), as well as the alpha(1D)-adrenoceptor-selective antagonist 8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9-dione (BMY-7378; 1-3 mg/kg), were used to determine the subtype(s) involved. Evoked mydriasis was significantly antagonized by both WB-4101 and 5-methylurapidil but not by BMY-7378. These results suggest that, unlike some other species, adrenoceptors in the rat iris dilator mediating neurogenic mydriasis are "typical" and, in addition, can be characterized as being primarily of the alpha(1A)-adrenoceptor subtype.

Surfactant and corticosteroid effects on lung function in a rat model of acute lung injury

OBJECTIVES

To evaluate pulmonary responses to intratracheal administration of surfactant with and without dexamethasone in rats with paraquat-induced lung injury.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research facility.

SUBJECTS

Adult male Sprague Dawley rats.

INTERVENTIONS

Rats were anesthetized and underwent a tracheostomy and arterial catheter insertion 3 days after intraperitoneal injection of paraquat (35 mg/kg). The rats were ventilated for 90 mins after sequential designation as controls or as recipients of intratracheal surfactant alone (50 or 100 mg/kg) or surfactant (50 or 100 mg/kg) plus dexamethasone (0.5 mg/kg).

MEASUREMENTS AND MAIN RESULTS

Arterial blood gases were determined at 15, 30, 60, and 90 mins. After 90 mins of ventilation, a static pressure-volume curve was performed, and inflammatory cells, total protein content, and cytokines were measured in bronchoalveolar lavage fluid. Postmortem histology was then examined. Treatment with 50 mg/kg dexamethasone/Survanta and 100 mg/kg Survanta with and without dexamethasone significantly increased oxygenation shortly after instillation when compared with the control group, with the response maintained throughout the study period. Static pressure-volume curves showed that the group receiving 100 mg/kg dexamethasone/Survanta had significantly higher lung volumes than the control group. Total cell, neutrophil, and macrophage counts were decreased significantly in the animals treated with 100 mg/kg dexamethasone/Survanta compared with untreated control rats. Total protein recovered from bronchoalveolar lavage fluid in the animals treated with 100 mg/kg Survanta with and without dexamethasone was decreased significantly compared with control animals. The histologic appearance of the lungs was markedly better in the groups treated with surfactant with or without dexamethasone.

CONCLUSIONS

Results suggest that the combined administration of high doses of intratracheal surfactant and dexamethasone improves gas exchange, ameliorates lung inflammation, and alleviates lung damage after paraquat-induced lung injury. Surfactant alone and lower doses of surfactant plus dexamethasone had a lesser effect on these measures.

Allosteric interactions between the antagonist prazosin and amiloride analogs at the human alpha(1A)-adrenergic receptor

It has been demonstrated previously that amilorides can interact with a well defined allosteric site on the human alpha(2A)-adrenergic receptor. In this study, the question was explored as to whether the human alpha(1A)-adrenergic receptor also possesses an equivalent allosteric site. The six amilorides examined strongly increased the dissociation rate of the antagonist [(3)H]prazosin from the alpha(1A)-adrenergic receptor in a concentration-dependent manner. With the parent amiloride, the dissociation data were well fitted by an equation derived from the ternary complex allosteric model, compatible with amiloride acting at a defined allosteric site on the alpha(1A)-adrenergic receptor. In contrast, the dissociation data for [(3)H]prazosin in the presence of the amiloride analogs were not compatible with the equation derived from a one-allosteric-site model, but could be fitted well by an equation derived from a two-allosteric-site model. However, certain individual parameters could not be resolved. The observed dissociation rate constants increased steeply with increasing amiloride analog concentration, and in some cases the data could be fitted with a logistic equation. The slope factors calculated from such fits were 1.2 to 2.1. It is concluded that the structure-binding relationships of the amilorides at the alpha(1A)- and alpha(2A)-adrenergic receptors are different. The interactions of the five amiloride analogs, but not the parent amiloride, with the alpha(1A)-adrenergic receptor are compatible with the presence of two (but not one) allosteric sites, and is thus more complex than that found for the alpha(2A)-adrenergic receptor.

Eotaxin and eotaxin receptor (CCR3) expression in Sephadex particle-induced rat lung inflammation

The beta chemokine eotaxin is a potent eosinophil activator and chemoattractant. We examined immunohistochemically eotaxin protein expression in a range of normal rat tissues and in rat lung during Sephadex particle-induced pulmonary inflammation. The time course of eotaxin expression in lung at various time points after Sephadex administration was related to the appearance of eosinophils in the bronchoalveolar lavage fluid and tissue distribution of eotaxin receptor (CCR3) positive cells. Results showed that eotaxin protein was constitutively expressed by both lung airway epithelial cells and gut epithelial cells in normal tissues in the absence of inflammation. During Sephadex induced pulmonary inflammation, eotaxin expression increased in alveolar macrophages prior to the major increase in eosinophil numbers which reached a peak at 72 h. The pattern of eotaxin pulmonary expression and the location of CCR3 receptor positive cells suggest a chemoattractant gradient resulting in migration firstly into the tissue and subsequently through the airway epithelium into the airways. Treatment of rats with the glucocorticoid dexamethasone or the immunosuppressant cyclosporin A reduced eosinophil entry into lung tissue and airways but had no apparent effect on eotaxin expression in vivo, indicating that both these drugs inhibit eosinophil recruitment either by an eotaxin-independent mechanism, or by targetting factors that synergise with eotaxin, or an event post eotaxin expression.