Cholinergic responsiveness of respiratory and vascular tissues in two different rat strains

Effect of combined nitrogen dioxide and carbon nanoparticle exposure on lung function during ovalbumin sensitization in Brown Norway rat

The interaction of particulate and gaseous pollutants in their effects on the severity of allergic inflammation and airway responsiveness are not well understood. We assessed the effect of exposure to NO₂ in the presence or absence of repetitive treatment with carbon nanoparticle (CNP) during allergen sensitization and challenges in Borwn-Norway (BN) rat, in order to assess their interactions on lung function and airway responses (AR) to allergen and methacholine (MCH), end-expiratory lung volume (EELV), bronchoalveolar lavage fluid (BALF) cellular content, serum and BALF cytokine levels and histological changes. Animals were divided into the following groups (n = 6): Control; CNP (Degussa-FW2): 13 nm, 0.5 mg/kg instilled intratracheally ×3 at 7-day intervals; OVA: ovalbumin-sensitised; OVA+CNP: both sensitized and exposed to CNP. Rats were divided into equal groups exposed either to air or to NO₂, 10 ppm, 6 h/d, 5d/wk for 4 weeks. Exposure to NO₂, significantly enhanced lung inflammation and airway reactivity, with a significantly larger effect in animals sensitized to allergen, which was related to a higher expression of TH1 and TH2-type cytokines. Conversely, exposure to NO₂ in animals undergoing repeated tracheal instillation of CNP alone, increased BALF neutrophilia and enhanced the expression of TH1 cytokines: TNF-α and IFN-γ, but did not show an additive effect on airway reactivity in comparison to NO₂ alone. The exposure to NO₂ combined with CNP treatment and allergen sensitization however, unexpectedly resulted in a significant decrease in both airway reactivity to allergen and to methacholine, and a reduction in TH2-type cytokines compared to allergen sensitization alone. EELV was significantly reduced with sensitization, CNP treatment or both. These data suggest an immunomodulatory effect of repeated tracheal instillation of CNP on the proinflammatory effects of NO₂ exposure in sensitized BN rat. Furthermore, our findings suggest that NO₂, CNP and OVA sensitization may significantly slow overall lung growth in parenchymally mature animals.

Involvement of COX-1 in A3 adenosine receptor-mediated contraction through endothelium in mice aorta

We investigated whether A(3) adenosine receptor (A(3)AR) is involved in endothelium-mediated contraction through cyclooxygenases (COXs) with the use of wild-type (WT) and A(3) knockout (A(3)KO) mice aorta. A(3)AR-selective agonist, Cl-IBMECA, produced a concentration-dependent contraction (EC(50): 2.9 +/- 0.2 x 10(-9) M) in WT mouse aorta with intact endothelium (+E) and negligible effects in A(3)KO +E aorta. At 10(-7) M, contractions produced by Cl-IBMECA were 29% in WT +E, while being insignificant in A(3)KO +E aorta. Cl-IBMECA-induced responses were abolished in endothelium-denuded tissues (-E), in both WT and A(3)KO aorta. A(3)AR gene and protein expression were reduced by 74 and 72% (P < 0.05), respectively, in WT -E compared with WT +E aorta, while being undetected in A(3)KO +E/-E aorta. Indomethacin (nonspecific COXs blocker, 10(-5) M), SC-560 (specific COX-1 blocker, 10(-8) M), SQ 29549 (thromboxane prostanoid receptor antagonist, 10(-6) M), and furegrelate (thromboxane synthase inhibitor, 10(-5) M) inhibited Cl-IBMECA-induced contraction significantly. Cl-IBMECA-induced thromboxane B(2) production was also attenuated significantly by indomethacin, SC-560, and furegrelate in WT +E aorta, while having negligible effects in A(3)KO +E aorta. NS-398 (specific COX-2 blocker) produced negligible inhibition of Cl-IBMECA-induced contraction in both WT +E and A(3)KO +E aorta. Cl-IBMECA-induced increase in COX-1 and thromboxane prostanoid receptor expression were significantly inhibited by MRS1523, a specific A(3)AR antagonist in WT +E aorta. Expression of both A(3)AR and COX-1 was located mostly on endothelium of WT and A(3)KO +E aorta. These results demonstrate for the first time the involvement of COX-1 pathway in A(3)AR-mediated contraction via endothelium.

Male sex hormones promote vagally mediated reflex airway responsiveness to cholinergic stimulation

A sex disparity in airway responsiveness to cholinergic stimulation has been observed in laboratory mice in that males are considerably more responsive than females, but the basis for this difference is unclear. In this report, we demonstrate that male sex hormones promote murine airway responsiveness to cholinergic stimulation via vagus nerve-mediated reflex mechanisms. In tissue bath preparations, no sex-based differences were observed in the contractile responses of isolated tracheal and bronchial ring segments to carbachol, indicating that the mechanism(s) responsible for the in vivo sex difference is (are) absent ex vivo. Bilateral cervical vagotomy was found to abolish in vivo airway responsiveness to methacholine in male mice, whereas it did not alter the responses of females, suggesting a regulatory role for male sex hormones in promoting reflex airway constriction. To test this possibility, we next studied mice with altered circulating male sex hormone levels. Castrated male mice displayed airway responsiveness equivalent to that observed in intact females, whereas administration of exogenous testosterone to castrated males restored responsiveness, albeit not to the level observed in intact males. Administration of exogenous testosterone to intact female mice similarly enhanced responsiveness. Importantly, the promotive effects of exogenous testosterone in castrated male and intact female mice were absent when bilateral vagotomy was performed. Together, these data indicate that male sex hormones promote cholinergic airway responsiveness via a vagally mediated reflex mechanism that may be important in the regulation of airway tone in the normal and diseased lung.

Acetylcholine causes endothelium-dependent contraction of mouse arteries

The goal of this study was to determine whether acetylcholine evokes endothelium-dependent contraction in mouse arteries and to define the mechanisms involved in regulating this response. Arterial rings isolated from wild-type (WT) and endothelial nitric oxide (NO) synthase knockout (eNOS−/−) mice were suspended for isometric tension recording. In abdominal aorta from WT mice contracted with phenylephrine, acetylcholine caused a relaxation that reversed at the concentration of 0.3–3 μM. After inhibition of NO synthase [with Nω-nitro-l-arginine methyl ester (l-NAME), 1 mM], acetylcholine (0.1–10 μM) caused contraction under basal conditions or during constriction to phenylephrine, which was abolished by endothelial denudation. This contraction was inhibited by the cyclooxygenase inhibitor indomethacin (1 μM) or by a thromboxane A2 (TxA2) and/or prostaglandin H2 receptor antagonist SQ-29548 (1 μM) and was associated with endothelium-dependent generation of the TxA2 metabolite TxB2. Also, SQ-29548 (1 μM) abolished the reversal in relaxation evoked by 0.3–3 μM acetylcholine and subsequently enhanced the relaxation to the agonist. The magnitude of the endothelium-dependent contraction to acetylcholine (0.1–10 μM) was similar in aortas from WT mice treated in vitro with l-NAME and from eNOS−/− mice. In addition, we found that acetylcholine (10 μM) also caused endothelium-dependent contraction in carotid and femoral arteries of eNOS−/− mice. These results suggest that acetylcholine initiates two competing responses in mouse arteries: endothelium-dependent relaxation mediated predominantly by NO and endothelium-dependent contraction mediated most likely by TxA2.

Regionally different influence of contractile agonists on isolated rat airway segments

Rats are increasingly used to study airway inflammation and bronchial responsiveness. Relative little is known on the contribution of small airways in this animal model. We therefore compared the responsiveness to various inflammatory agents of isolated trachea, main bronchi (using classic organ bath) and isolated bronchioles (using small myograph) from Wistar and Fisher 344 rats. The largest contraction was elicited on all preparations by carbachol. Histamine elicited a (small) contraction only on bronchioles. The contractions elicited by serotonin, bradykinin, and the thromboxane A2-mimetic U-46619 were always relatively larger in bronchioles than in trachea and main bronchi. The sensitivities to carbachol and serotonin were smaller in bronchioles. The tachykinins substance P and neurokinin A elicited no substantial contraction on bronchioles or main bronchi. Trachea of Fisher 344 but not of Wistar rats showed a small contraction. No other differences were found between preparations from Wistar and Fisher 344 rats. It is concluded that rat trachea, main bronchi and small bronchioles show regional and strain-dependent variations in their responsiveness to contractile agents.