Hyperresponsive Rats Research Articles

Captopril Suppresses Polybrominated Diphenyl ether‐induced Pressor responses and Upregulation of RAAS gene markers Nr3c2 and Sgk1 Under Salt Loading in Rats

Polybrominated Diphenyl Ethers (PBDEs) are organohalogens used as flame retardants in industries ranging from textiles to electronics, and are ubiquitous in our household environments. PBDEs are endocrine disrupting pollutants, and are toxic to the kidney and nervous system. We have previously shown that early life exposure to PBDEs permanently affects the cardiovascular system. In a previous report we demonstrated that perinatal exposure to PBDEs significantly exacerbates hyperosmotic‐induced pressor in adult rats. Follow up studies revealed that PBDE‐induced exaggerated blood pressure responses to stress are suppressed by the angiotensin converting enzyme (ACE) inhibitor and the mineralocorticoid receptor blocker, spironolactone, suggesting involvement of the Renin‐Angiotensin‐Aldosterone System (RAAS), including the kidney, in PBDE actions. Here we tested the hypothesis that developmental exposure to PBDEs enhance kidney RAAS processes in hyperresponsive rats. Dams were dosed perinatally from gestation day (GD) 4 to postnatal day (PND) 20 (except on day 0) with DE‐71, an industrial mixture of penta‐brominated and other PBDE congeners. At PND 60, baseline measures of systolic and mean arterial pressure and heart rate were recorded using non‐invasive blood pressure (NIBP) monitoring under isoflurane anesthesia (4% induction; 1.75% maintenance). Then, captopril was administered ad libitum via drinking water for two weeks. On the day of the experiment rats were hyperosmotically stimulated (3.5 M NaCl, 0.6ml/100 g b.w., i.p.) and 3 hours later NIBP measures recorded. Kidney gene expression was compared across hyperosmotically challenged and normosmotic rats that were exposed to PBDEs or oil vehicle (control), and treated with captopril or not. Using q‐PCR we examined gene markers for terminal RAAS effectors in the kidney and expressed as fold‐expression relative to the reference gene, b‐actin (Actb): mineralocorticoid receptor (Nr3c2); serum glucocorticoid kinase 1 (Sgk1), transcription of which is acutely regulated by Nr3c2 activation; and the Nr3c2 substrate regulator, hydroxysteroid 11‐betadehydrogenase 1 (Hsd11b1). A two‐way ANOVA revealed a significant main effect of captopril (p=0.00195) and PBDE (p=0.0423) on Nr3c2 gene expression. Post hoc comparisons revealed significant reductions in Nr3c2 fold expression between oil controls without and with captopril (p=0.0430; 1.024 ± 0.11 vs. 0.745 ± 0.099, n=4–5) and between PBDE exposed rats without and with captopril (p=0.0072; 1.252 ± 0.07 vs. 0.895 ± 0.101, n=5–6), indicating a novel mechanism of action of captopril on RAAS. We also demonstrate that relative to controls (n=5), PBDEs (n=6) significantly increased Sgk1 fold gene expression (p=0.042; 1.796 ± 0.432 vs. 1.082 ± 0.224, respectively), indicating a novel mechanism of action for PBDEs that may lead to acute salt‐induced hypertension via epithelial Na(+) channels (ENaC). Importantly, the PBDE upregulation of Sgk1 can be blocked by captopril.Support or Funding InformationSupported by APS (J.L., D.P.), MARC (R.G.), and Sigma Xi Research Society (J.L.).

Anti-asthmatic effects of type-A procyanidine polyphenols from cinnamon bark in ovalbumin-induced airway hyperresponsiveness in laboratory animals

Increased sensitivity to bronchoconstricting agents, airway inflammation and airflow obstruction are the characteristic feature of the asthma. The present study aimed to study the anti-asthmatic potential of type-A procyanidine polyphenols (TAPP) isolated from Cinnamon (Cinnamomum zeylanicum Syn C. verum, family: Lauraceae) bark against ovalbumin (OVA)-induced airway hyperresponsiveness (AHR) in laboratory animals. Preparation and characterization of TAPP from cinnamon bark was carried out. The AHR was induced in the male Wistar rats by intraperitoneal (i.p.) injection of OVA and boosted with an identical OVA solution (s.c.) on day 7. Rats received oral treatment of TAPP (10, 30 and 100mg/kg) from day 7 to day 14. After completion of treatment, the rats were challenged with OVA-aerosol intranasal administration (i.n.). The behavioral (lung function test), biochemical (total and differential cell count, level of albumin, nitric oxide (NO) and total protein in serum, lungs and bronchalveolar lavage fluid, bronchoalveolar lavage fluid (BALF)) and histopathological (lung) assessments were performed. Characterization data (HPLC fingerprinting) showed the presence of pentameric procyanidine flavonoid in TAPP (purity – 75.9%). Treatment with TAPP (100mg/kg) showed the significant decrease (P<0.001) in breathing rate and PIF whereas the PEF and FEV expired in one second (FEV1) was significantly increased (P<0.001) as compared to AHR control rats. TAPP also showed the significant increase (P<0.01) in the level of hemoglobin, RBCs and WBCs. TAPP (100mg/kg) treatment significantly (P<0.001) reduced the elevated levels of total protein (lung and BALF), albumin (serum, BALF and lung), goblet cell hyperplasia and inflammatory cell infiltration in lung tissue in OVA-induced hyperresponsive rats. In conclusion, TAPP showed anti-asthmatic effects in OVA-induced hyperresponsive rat model and may have potential therapeutic value for the management of asthma.

Rebuttal from Gunst and Panettieri

Rebuttal from Gunst and Panettieri

Glucocorticoids inhibited airway hyperresponsiveness through downregulation of CPI-17 in bronchial smooth muscle

Glucocorticoids are the most effective anti-inflammatory treatment for asthma, and inhaled corticosteroids are the most effective long-term control therapy for persistent asthma. In the present study, to determine the mechanism of the inhibitory effect of glucocorticoids on airway hyperresponsiveness, the effects of glucocorticoids on the expression and activation of PKC-potentiated protein phosphatase 1 inhibitory protein of 17 kDa (CPI-17) were examined in bronchial smooth muscles of antigen-induced airway hyperresponsive rats. Repeated antigen inhalation to animals sensitized with DNP- Ascaris antigen caused a marked bronchial smooth muscle hyperresponsiveness to acetylcholine, accompanied by upregulation and acetylcholine-induced activation of CPI-17 to result in an increase in myosin light chain (MLC) phosphorylation. Treatment with glucocorticoids (prednisolone or beclomethasone, 10 mg/kg, i.p., respectively) significantly inhibited the airway hyperresponsiveness, and markedly reduced both the protein and mRNA levels of CPI-17 in bronchial smooth muscle. The acetylcholine-induced activation of CPI-17, i.e., phosphorylation of CPI-17, was also significantly inhibited by glucocorticoids. Glucocorticoids also prevented the augmented acetylcholine-induced MLC phosphorylation observed in the airway hyperresponsive rats. Therefore, glucocorticoids might inhibit the airway hyperresponsiveness through the inhibition of overexpression and activation of CPI-17.

Augmentation of Endothelin-1-Induced Phosphorylation of CPI-17 and Myosin Light Chain in Bronchial Smooth Muscle from Airway Hyperresponsive Rats

Airway hyperresponsiveness (AHR) associated with heightened airway resistance and inflammation is a characteristic feature of bronchial asthma. It has been demonstrated that contraclile responsiveness to endothelin-1 (ET-1) in repeated antigen challenge-induced airway hyperresponsive bronchial preparation was significantly increased. ET-1 is a potent contracting substance for various smooth muscles including airways. In addition to the classical Ca(2+)-mediated contraction, ET-1 also induced Ca(2+) sensitization of contraction. However, it is not clear whether ET-1 stimulation also activates the CPI-17 (PKC-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) pathway in airway smooth muscles. Therefore, the changes in ET-1-induced activation/phosphorylation of CPI-17 and myosin light chain (MLC) in bronchial smooth muscle of repeatedly antigen-challenged rats were examined. The levels of ET-1-induced phosphorylation of CPI-17 and MLC were increased much more markedly in the AHR group than in the sensitized control animals. It might be suggested that the augmented activation of CPI-17 observed in the hyperresponsive bronchial smooth muscle is responsible for the enhanced agonists-induced contraction of bronchial smooth muscle in AHR rats.

Possible Involvement of CPI-17 in Augmented Bronchial Smooth Muscle Contraction in Antigen-Induced Airway Hyper-Responsive Rats

Airway hyper-responsiveness (AHR) associated with heightened airway resistance and inflammation is a characteristic feature of asthma. It has been demonstrated that contractile responsiveness and Ca(2+) sensitization to acetylcholine (ACh) in repeated antigen challenge-induced airway hyper-responsive bronchial preparation were significantly increased. The CPI-17 (PKC-potentiated inhibitory protein for heterotrimeric myosin light chain phosphatase of 17 kDa) is activated by protein kinase C and acts on a myosin light-chain phosphatase-specific target. The aim of the present study was to explore the role of CPI-17 in hyper-responsiveness of bronchial smooth muscle in antigen-induced AHR rats. In immunoblotting, the levels of expression of CPI-17 mRNA and protein were significantly increased in bronchus from rats that were repeatedly challenged with antigen. ACh-induced CPI-17 phosphorylation and translocation to membrane fraction were also significantly increased in bronchus from antigen-challenged rats. In conclusion, we suggest that augmented expression and activation of CPI-17 observed in the hyper-responsive bronchial smooth muscle might be responsible for the enhanced ACh-induced Ca(2+) sensitization of bronchial smooth muscle contraction associated with AHR.

Modulation by sudden darkness of apomorphine-induced behavioral responses

Sudden darkness increases motor activity and decreases anxiety. In the present study, we focused on the role of dopaminergic mechanisms involved in the effects of sudden darkness. The influence of sudden darkness on the behavioral effects of low (0.05 and 0.1 mg/kg) and high (0.25, 0.45 and 0.6 mg/kg) doses of apomorphine (APO) was tested. We assayed the effects of low APO doses on yawning–penile erection syndrome (YES; 0.05 and 0.1 mg/kg) and on motor activity (0.05 mg/kg), and the effects of high APO doses on motor activity (0.25 mg/kg) and stereotyped behavior (0.45 mg/kg and 0.6 mg/kg). Spontaneous total and genital grooming of male and female rats were also recorded. Sudden darkness modified some spontaneous behaviors and also modulated several APO-induced behavioral effects. It increased spontaneous total grooming and genital grooming in male rats but had no effect on these parameters in female rats. These results show sexual dimorphism for total and genital grooming in both control and sudden darkness conditions. APO was able to induce YES in a dose-dependent manner. Sudden darkness decreased yawning elicited by both 0.05 and 0.1 mg/kg of the drug. No other parameter of YES was modified. In the open-field test, sudden darkness increased total locomotion and rearing and decreased immobility duration. APO at a dose of 0.05 mg/kg had the opposite effect on these parameters under light conditions; none of them were modified by sudden darkness. Animals treated with APO at 0.25 mg/kg, a dose that augmented total locomotion and rearing and diminished immobility duration, were clearly divided into two groups according to their responses, i.e., hypo- and hyper-responsive rats. Sudden darkness improved total locomotion and rearing, reduced immobility duration and total grooming in the hyporesponsive group, and showed no effects on the hyper-responsive group. Sudden darkness caused no modifications of stereotyped behavior. These results may be due to a sudden darkness-induced physiological release of dopamine that diminishes pre-synaptic responses to APO and increases low-intensity post-synaptic responses such as motor activity without modifying high-intensity post-synaptic responses such as stereotyped behavior.

Upregulation of rhoA mRNA in bronchial smooth muscle of antigen-induced airway hyperresponsive rats.

It has recently been suggested that RhoA plays an important role in the enhancement of Ca2+ sensitization observed in smooth muscle contraction. In the present study, the expression of rhoA mRNA in the bronchial smooth muscle of antigen-induced airway hyperresponsive rats was compared with that of control animals. Reverse transcription-polymerase chain reaction experiments using total RNA from these tissue specimens and the specific primers revealed rhoA mRNA to be expressed in bronchial smooth muscle of the rat. The rhoA mRNA expression in bronchial smooth muscle of the hyperresponsive rats was significantly increased in comparison to that of control animals. It is thus possible that upregulation of RhoA protein might be involved in the mechanism underlying the increased contractility of the bronchial smooth muscle which occurs with airway hyperresponsiveness.

Augmented acetylcholine-induced translocation of RhoA in bronchial smooth muscle from antigen-induced airway hyperresponsive rats

Acetylcholine (ACh)-induced translocation of RhoA in bronchial smooth muscle of repeatedly antigen-challenged rats that have a marked airway hyperresponsiveness (AHR) was examined. ACh induced time- and concentration-dependent translocation of RhoA to the plasma membrane, indicating an activation of RhoA in bronchial smooth muscle. The level of ACh-induced RhoA translocation was further increased markedly in the AHR group as compared to that in the control group. It is suggested that the augmented activation of RhoA observed in the hyperresponsive bronchial smooth muscle might be responsible for the enhanced ACh-induced Ca(2+) sensitization of bronchial smooth muscle contraction associated with AHR.

Effect of gabapentin and lamotrigine on mechanical allodynia-like behaviour in a rat model of trigeminal neuropathic pain

Injury to the trigeminal nervous system may induce severe pain states. This study examined the antinociceptive effect of the novel anticonvulsants, gabapentin and lamotrigine, in a rat model of trigeminal neuropathic pain produced by chronic constriction of one infraorbital nerve. Responsiveness to von Frey filament stimulation of the vibrissal pad was evaluated 2 weeks post-operation. Hyper-responsive rats received acute and repeated (five injections separated by the half-life of the compound) injections with gabapentin and lamotrigine. 76% of the nerve-injured rats displayed pronounced hyper-responsiveness (median 0.217 g (lower–upper percentiles 0.217–0.217) vs. 12.5 g pre-operative), that was resistant to both single (5–100 mg/kg) and repeated (5–30 mg/kg) injections with i.p. lamotrigine. Repeated (30 and 50 mg/kg), but not single (30–100 mg/kg) injections of i.p. gabapentin partially alleviated the mechanical allodynia-like behaviour. Repeated injections of gabapentin at 50 but not at 30 mg/kg produced motor deficits. The results indicate that gabapentin rather than lamotrigine may be a better therapeutic approach for the clinical management of some trigeminal neuropathic pain disorders.

Increased expression of G12 and G13 proteins in bronchial smooth muscle of airway hyperresponsive rats

To obtain information on the activation pathway of the monomeric G protein, RhoA, in bronchial smooth muscle, the expression of G alpha12 and G alpha13 in bronchial smooth muscle of the rat was determined. The levels of these G proteins were also compared between antigen-induced airway hyperresponsive and normal control groups. Actively sensitized rats were repeatedly challenged by antigen inhalation. Twenty-four hours after the final antigen challenge, membrane preparations of bronchial smooth muscles were prepared. Immunoblottings were performed, and the density ratios of G alpha12/beta-actin and G alpha13/beta-actin were calculated to quantify the levels of these G-protein alpha subunits. Both G alpha12 and G alpha13 proteins were expressed in rat bronchial smooth muscle. The levels of bronchial G alpha12 and G alpha13 proteins in the repeatedly antigen challenged rats were significantly increased as compared with those in control animals; the magnitude of upregulation in the airway-hyperresponsive group was 89% and 68% in the control group, respectively. G alpha12 and G alpha13 proteins were expressed in rat bronchial smooth muscle. Considering the probable involvement of G12 and G13 proteins in Ca2+ sensitization through Rho protein, the augmented expression of such G proteins after repeated antigen challenge may be responsible for the hyperresponsiveness of bronchial smooth muscle contraction in rats.

Possible involvement of G i3 protein in augmented contraction of bronchial smooth muscle from antigen-induced airway hyperresponsive rats

To investigate a possible involvement of pertussis toxin (PTX)-sensitive heterotrimeric G proteins in the pathogenesis of airway hyperresponsiveness, the effect of PTX treatment on the augmented contractile response to acetylcholine (ACh) in bronchial smooth muscle of antigen-induced airway hyperresponsive rats was determined. In bronchial smooth muscle of airway hyperresponsive rats that were actively sensitized and repeatedly challenged with 2,4-dinitrophenylated Ascaris suum antigen, ACh-induced contractions were markedly augmented. The augmented contractile responses in the airway hyperresponsive group were significantly inhibited after treatment with PTX (1 μg/mL for 6 hr, 37°), whereas only a slight attenuation was observed in the normal control group. The level of Gα i3 (measured by immunoblotting), but not other α-subunits of G i/o family proteins, in bronchial smooth muscle of the airway hyperresponsive rats was significantly increased as compared with that of control animals. It is concluded that PTX-sensitive muscarinic contractile responses of bronchial smooth muscle might be augmented upon antigen-induced airway hyperresponsiveness in rats, probably due to an up-regulation of Gα i3 protein of bronchial smooth muscle.

Inositol (1,4,5)Trisphosphate Metabolism and Enhanced Calcium Mobilization in Airway Smooth Muscle of Hyperresponsive Rats

Airway hyperresponsiveness (AHR) is a phenotype of asthma and can be modeled by the inbred Fisher strain of rat, which is hyperresponsive in vivo relative to the Lewis strain. Enhanced airway smooth muscle (ASM) contractility and Ca(2+) mobilization are associated with the AHR observed in Fisher rats. In this study, we investigated whether the interstrain differences in Ca(2+) mobilization to serotonin (5HT) result from differences in inositol (1,4,5)trisphosphate (IP(3)) metabolism and/or IP(3) receptor (IP(3)R) sensitivity. Ca(2+) mobilization by 5HT in cultured ASM cells from both rat strains was phospholipase C (PLC) dependent. Inositol polyphosphate accumulation, and hence PLC activity, was similar in both rat strains, but a specific IP(3) transient was detectable only in Fisher myocytes in response to 5HT. These findings suggested that IP(3) degradation rather than production differed between the two strains. The Vmax and Michaelis constant (K(m)) of IP(3)-specific 5-phosphatase activity were higher in the particulate fraction of Lewis than in Fisher ASM cell homogenates and appeared to be related to a greater expression of two isoforms of 5-phosphatase (type I and type II) in Lewis cells as shown by Western blot analysis. The sensitivity of the IP(3)R to IP(3) was similar between Fisher and Lewis ASM cells, indicating that the interstrain intracellular Ca(2+) differences were unrelated to IP(3)R function. We propose that interstrain variations in 5-phosphatase activity and expression may give rise to the interstrain differences in IP(3)-mediated Ca(2+) release in ASM and may be a determinant of AHR.

Gq protein level increases concurrently with antigen-induced airway hyperresponsiveness in rats

In the present study, bronchial Gq protein level of the airway hyperresponsive rats was determined by using immunoblot analysis. In the airway hyperresponsive rats that were sensitized and repeatedly antigen challenged, the in vitro bronchial responsiveness to acetylcholine was significantly enhanced as compared with that in the sensitized control group. Moreover, the bronchial contraction induced by 10 μM AlF 4 − (generated by 10 μM AlCl 3 plus 10 mM NaF) was significantly elevated after repeated antigen challenge (0.44±0.13 and1.09±0.09 g tension in the control and airway hyperresponsive groups, respectively; P<0.01). In both groups, immunoblotting with the antibody against Gαq gave a single 42 kD band. The Gαq protein levels in the airway hyperresponsive group (0.58±0.12) estimated by Gαq/β-actin ratio was significantly greater than those in the control group (0.30±0.10; P<0.05). These findings suggest that the increase in Gαq protein level may be involved in the pathogenesis of antigen-induced airway hyperresponsiveness in rats.

Protein kinase C is involved in enhanced airway smooth muscle cell growth in hyperresponsive rats.

Fischer rat airway smooth muscle (ASM) models two potential risk factors for asthma: hyperresponsiveness to contractile agonists and to growth stimuli. The aim of this study was to identify the mechanisms responsible for enhanced ASM mitogenic response in Fischer rats compared with the control Lewis strain. The enhanced Fischer ASM cell growth response to fetal bovine serum (FBS) could not be accounted for by phospholipase C, mitogen-activated protein kinases, or tyrosine kinase activities as assessed by pharmacological inhibition and Western blotting. In contrast, depletion of phorbol ester-sensitive isoforms of the serine/threonine kinase protein kinase C (PKC) removed the difference in growth response between the rat strains. Additionally, FBS selectively induced serine/threonine phosphorylation of a 115-kDa protein in Fischer ASM cells. Enhanced activation of PKC-betaI and decreased activation of PKC-delta in Fischer compared with Lewis cells following FBS stimulation were suggested by Western blotting of membrane and cytosolic fractions. The data are consistent with a role for PKC in the enhanced ASM cell growth of hyperresponsive rats.

P-505 - Pharmacological studies on the respiratory tract (Rept 226): Acetylcholine-induced translocation of RhoA is augmented in bronchial smooth muscle of airway hyperresponsive (AHR) rats

P-505 - Pharmacological studies on the respiratory tract (Rept 226): Acetylcholine-induced translocation of RhoA is augmented in bronchial smooth muscle of airway hyperresponsive (AHR) rats

Acetylcholine-Induced Smooth Muscle Contraction of Intrapulmonary Small Bronchi Is Augmented in Antigen-Induced Airway Hyperresponsive Rats

Smooth muscle responsiveness of intrapulmonary small bronchi obtained from repeatedly antigen-challenged rats was compared with that from control animals to determine whether smooth muscle contractility of peripheral airways is augmented by such repeated challenge. In intact (non-permeabilized) smooth muscles of intrapulmonary bronchi, the acetylcholine (ACh)-induced contractile response was significantly augmented in the repeated challenge group, although 60-mM K+-induced contraction was within the normal level. In beta-escin-permeabilized muscles, no significant difference between groups was observed in the Ca2+-induced contractile responses. Thus, augmented ACh-induced contraction of intact intrapulmonary small bronchial smooth muscle might be, at least in part, due to an enhanced ACh-mediated Ca2+-sensitizing signal.

ELEVATED NITRIC OXIDE SYNTHASE ACTIVITY CONCURRENT WITH ANTIGEN-INDUCED AIRWAY HYPERRESPONSIVENESS IN RATS

To characterize the airway nitric oxide synthase (NOS) activities concurrent with airway hyperresponsiveness (AHR), a common feature of allergic asthma, the NOS activities of airway tissue homogenates from the antigen-induced AHR rats were determined by the ability of tissue homogenates to convert L-arginine to L-citrulline (Cit). A significantly higher level of total NOS activities was found in homogenates from the AHR rats (19.9 +/- 1.3 pmol Cit/min/mg protein) compared to those from sensitized control and normal control groups (9.8 +/- 1.2 and 8.8 +/- 1.2 pmol Cit/min/mg protein, respectively; P < .01). The nitrite concentration in bronchoalveolar lavage fluids, which indicates the in vivo generation of NO in airways, from the AHR rats (7.40 +/- 0.71 microM) was significantly greater than that from nonsensitized normal animals (1.45 +/- 1.12 microM, P < .01). Although the protein levels of endothelial (eNOS) and neuronal type NOS (nNOS) determined by immunoblotting were within normal levels, the amount of inducible NOS (iNOS) protein was markedly and significantly elevated in airway tissue homogenates from the AHR rats. Immunohistochemical staining of airway tissues with specific antibody against iNOS demonstrated a distinct localization of iNOS on epithelial cells and infiltrated inflammatory cells in the bronchi of the hyperresponsive rats, but only negligible staining of epithelia was observed in the nonsensitized normal group. No difference in constitutive NOS (eNOS and nNOS) localization was observed between groups. The present findings indicate that the NOS activities in airway tissues are elevated in antigen-induced AHR rats, which is mainly derived from the induction of iNOS in the airways. Downregulation of constitutive eNOS and nNOS is not found in this animal model of AHR.

Augmented acetylcholine‐induced, Rho‐mediated Ca2+ sensitization of bronchial smooth muscle contraction in antigen‐induced airway hyperresponsive rats

Treatment with acetylcholine (ACh) of a beta-escin-permeabilized intrapulmonary bronchial smooth muscle of the rat induced force when the Ca2+ concentration was clamped at 1 microM. The ACh-induced Ca2+ sensitization of myofilaments was significantly greater in antigen-induced airway hyperresponsive rats than in control rats. The ACh-induced Ca2+ sensitization was completely blocked by treatment with Clostridium botulinum C3 exoenzyme, an inactivator of Rho family of proteins. Moreover, the protein level of RhoA in the intrapulmonary bronchi was significantly increased in the airway hyperresponsive rats. Thus, increased airway smooth muscle contractility observed in asthmatics may be related to augmented agonist-induced, Rho-mediated Ca2+ sensitization of myofilaments.

Probable involvement of the augmented agonist-induced Ca2+ sensitization of airway smooth muscle contraction in the pathogenesis of airway hyperresponsiveness

Nonspecific airway hyperresponsiveness (AHR) is a common feature of allergic bronchial asthmatics, but the underlying mechanism (s) of AHR have yet to be elucidated. The importance of AHR in the pathogenesis of asthma has been suggested by its relevance to the severity of this disease. There is thus a need to understand the underlying mechanisms of AHR for the sake of asthma therapy. In the present minireview, we discussed the involvement of the augmented agonist-induced Ca2+ sensitization of airway smooth muscle contraction in the pathogenesis of AHR. Treatment with acetylcholine (ACh) of a beta-escin-permeabilized intrapulmonary bronchial smooth muscle of the rat induced a stronger contractile force even when the Ca2+ concentration was clamped at 1 microM. The ACh-induced Ca2+ sensitization of myofilaments was found to be significantly greater in antigen-induced airway hyperresponsive rats than in control rats. The ACh-induced Ca2+ sensitization was completely blocked by treatment with Clostridium botulinum C3 exoenzyme, an inactivator of the Rho family proteins. Moreover, the protein level of RhoA in the intrapulmonary bronchi was demonstrated to be significantly increased in the airway hyperresponsive rats. Thus, the increased airway smooth muscle contractility observed in asthmatics may be related to the augmented agonist-induced, Rho-mediated Ca2+ sensitization of myofilaments.