Bronchoconstrictor reactivity to NKA in allergic dogs: a comparison to histamine and methacholine

Asthma: The Use of Animal Models and Their Translational Utility

Asthma is characterized by chronic lower airway inflammation that results in airway remodeling, which can lead to a permanent decrease in lung function. The pathophysiology driving the development of asthma is complex and heterogenous. Animal models have been and continue to be essential for the discovery of molecular pathways driving the pathophysiology of asthma and novel therapeutic approaches. Animal models of asthma may be induced or naturally occurring. Species used to study asthma include mouse, rat, guinea pig, cat, dog, sheep, horse, and nonhuman primate. Some of the aspects to consider when evaluating any of these asthma models are cost, labor, reagent availability, regulatory burden, relevance to natural disease in humans, type of lower airway inflammation, biological samples available for testing, and ultimately whether the model can answer the research question(s). This review aims to discuss the animal models most available for asthma investigation, with an emphasis on describing the inciting antigen/allergen, inflammatory response induced, and its translation to human asthma.

Comparison of barometric whole body plethysmography and its derived parameter enhanced pause (PENH) with conventional respiratory mechanics in healthy Beagle dogs

The purpose of the study was to compare barometric whole body plethysmography (BWBP) and its derived parameter, enhanced pause (PENH), with conventional respiratory mechanics measurements. Resistance (RL), dynamic compliance (Cdyn) and pleural pressure changes were measured in six healthy anaesthetised Beagle dogs using a pneumotachograph and oesophageal balloon technique consecutive to BWBP-derived variables. Upper airway airflow limitation was established (1) by a filter or (2) by insertion of a narrow endotracheal tube. Bronchoconstriction was induced by nebulisation of carbachol at increasing concentrations until PENH exceeded 300% baseline. Upper airway narrowing significantly increased resistance (baseline RL 2.0+/-0.3, RL filter 11.8+/-3.2, RL luminal narrowing 21.1+/-2.3cm H(2)O/L/s; P <0.03), whereas PENH did not change significantly (baseline PENH 0.55+/-0.17, PENH filter 0.49+/-0.10; PENH luminal narrowing 0.50+/-0.18; P >0.05). Carbachol-induced bronchoconstriction caused a significant increase in PENH (baseline PENH 0.43+/-0.14, PENH carbachol 2.62+/-2.14; P <0.02) and resistance (baseline RL 2.1+/-0.3, RL carbachol 28.8+/-13.0 cm H2O/L/s; P <0.01), and a pronounced drop in compliance (baseline Cdyn 163.3+/-73.9, Cdyn carbachol 9.7+/-2.9mL/cmH2O; P <0.02). It was concluded that BWBP detects airflow limitation due to bronchoconstriction but not due to upper airway obstruction in healthy dogs. BWBP represents a valid, although not very sensitive screening tool for respiratory function testing.

Canine models of asthma and COPD

Dogs have been extensively used to model the important components of asthma and COPD. Many of the key features of human asthma such as reversible airflow obstruction, pulmonary inflammation, airway hyperresponsiveness and cough are demonstrated in dogs after provocation with antigen, following a period of hyperventilation with dry air or after inhalation of ozone. Furthermore, standard anti-asthma drugs such as beta-adrenergic agonists, corticosteroids and leukotriene inhibitors are effective in these models. The pathology and pathophysiology of chronic bronchitis and emphysema can also be demonstrated in dogs after exposure to cigarette smoke, following inhalation of sulfur dioxide and by intra-tracheal or aerosol administration of proteolytic enzymes such as papain. These canine models of COPD have been used to evaluate a variety of new methodologies and treatments before they are tested in humans. This review highlights some of the important features of these canine models and how they have increased our understanding of the pathology, pathophysiology and control of human asthma and COPD.

Cough reflex in allergic dogs

This study investigated the effects of antigen challenge on the cough reflex in dogs that were neonatally sensitized to ragweed. Tidal volume (V(T)), respiratory rate (f), pulmonary resistance (R(L)), dynamic lung compliance (C(Dyn)) and the number and amplitude (increase in mean peak expiratory pressure) of coughs induced by mechanical stimulation of the intrathoracic trachea were measured in propofol-anesthetized dogs. Aerosolized ragweed challenge had no effect to induce spontaneous cough but increased f and R(L) and reduced V(T) and C(Dyn). Mechanical stimulation of the intrathoracic trachea at this time produced 19+/-5 coughs with an average increase in cough amplitude of 11+/-1 cm H(2)O which differed significantly from the number (9+/-2 coughs) and amplitude (30+/-5.5 cm H(2)O) of mechanically induced coughs after treatment with aerosolized saline. Both the number and amplitude of mechanically induced coughs returned to baseline values by 24-48 h after the ragweed challenge. Similar results were obtained after challenge with aerosolized histamine (0.3-1% histamine) that did not induce spontaneous coughs but increased f, reduced V(T) and decreased C(Dyn) and increased the number but reduced the amplitude of the mechanically induced coughs. In conclusion, both antigen and histamine bronchoprovocation changed the characteristics of the mechanically induced cough in dogs to a response of increased cough number but reduced mean expiratory cough amplitude.

Role of cholinergic reflexes on the bronchoconstrictor reactivity to neurokinin a in allergic dogs

Neurokinin A (NKA) potentiates airway cholinergic neurotransmission in several species. In this study, the role of cholinergic reflexes on the bronchoconstrictor response to NKA was evaluated in non-sensitized dogs and in allergic dogs neonatally sensitized to ragweed in which heightened bronchoconstrictor reactivity to NKA has previously been observed. Cardiopulmonary functions, including pulmonary resistance (R(L)) were measured in anesthetized, spontaneously breathing dogs before and after increasing concentrations of aerosolized NKA. The provocative concentrations of NKA increasing R(L) by 25% above the baseline (PC(25)) was measured before and after ( approximately 10 min) aerosolized saline or ipratropium bromide (0.01%). This concentration of ipratropium produced a 250-fold shift in the methacholine dose-response curve. In sensitized dogs, NKA bronchoconstrictor reactivity (PC(25)=0.050+/-0.011%) was 2.5 times more potent than that of non-sensitized controls (PC(25)=0.177+/-0.031%). Ipratropium bromide inhibited the bronchoconstrictor response to NKA in both sensitized and non-sensitized dogs and after ipratropium, NKA reactivity was 5.2-fold less in allergic dogs (PC(25)=0.246+/-0.048%) as compared to 3.5 fold less in non-sensitized controls (PC(25)=0.622+/-0.106%). In conclusion, cholinergic reflexes are important components of the bronchoconstrictor response to NKA in dogs particularly in those sensitized neonatally to ragweed. It is speculated that heightened activity of cholinergic reflexes contributes to the bronchial hyperresponsiveness seen in allergic dogs.