Involvement of A₁adenosine receptors and neural pathways in adenosine-induced bronchoconstriction in mice

Abstract

High levels of adenosine can be measured from the lungs of asthmatics, and it is well recognized that aerosolized 5'AMP, the precursor of adenosine, elicits robust bronchoconstriction in patients with this disease. Characterization of mice with elevated adenosine levels secondary to the loss of adenosine deaminase (ADA) expression, the primary metabolic enzyme for adenosine, further support a role for this ubiquitous mediator in the pathogenesis of asthma. To begin to identify pathways by which adenosine can alter airway tone, we examined adenosine-induced bronchoconstriction in four mouse lines, each lacking one of the receptors for this nucleoside. We show, using direct measures of airway mechanics, that adenosine can increase airway resistance and that this increase in resistance is mediated by binding the A(1) receptor. Further examination of this response using pharmacologically, surgically, and genetically manipulated mice supports a model in which adenosine-induced bronchoconstriction occurs indirectly through the activation of sensory neurons.

Adenosine induces airway hyperresponsiveness through activation of A3 receptors on mast cells

“…16 After the determination of basal mechanics (at 10-second intervals for 1 minute), mice were serially challenged with aerosolized methacholine (20 mg/mL, 40 mg/mL, and 80 mg/mL) for 20 seconds, and the R L , C dyn , R aw , and G tissue after each challenge were recorded every 10 seconds for 2 minutes.…”

“…16 After the preparation of tracheal rings, the preload tension was set to 0.5 g. The rings were treated with 10 µmol/L methacholine for 5 minutes, then washed and reset to 0.5 g resting tension, which was maintained throughout the 45-minute equilibration period. After a 10-minute pretreatment with vehicle, the rings were challenged with increasing concentrations (1 nmol/L to 10 µmol/L) of methacholine to establish dose-response curves.…”

“…To determine further whether A 1 adenosine receptors mediate adenosine-induced AHR indirectly (eg, via neural reflex as previously observed for adenosine-induced bronchoconstriction 16 ), we examined the capacity of NECA to induce AHR in A 1 -deficient mice, as described for wt mice. NECA pretreatment significantly enhanced methacholine-induced R L increases (Fig 2, A; P = .…”

“…8,9 By activating 4 G-protein-coupled adenosine receptors (A 1 , A 2A , A 2B , and A 3 ) on immunocytes, neurons, goblet cells, and ASM, adenosine is believed to contribute to asthma pathogenesis. [8][9][10][11][12][13][14][15][16][17][18][19][20] However, a role for adenosine in the development of AHR has not been previously investigated. In smooth muscle cells, Gerwins and Fredholm 21 demonstrated that adenosine could stimulate Ca 2+ mobilization and enhance the contractile response to activation of G q/11 -coupled receptors.…”

“…Female A 1 −/− and A 3 −/− mice were generated and genotyped as previously described, and backcrossed 12 generations to the C57BL/6 background. 16,23,24 Female C57BL/6 Kit W-sh/W-sh mast cell-deficient mice were bred in our animal facility. All mice were housed under pathogen-free conditions with 12-hour day and night switch.…”