Clenbuterol and Other B2-agonists-pulmonary Effects Other than Bronchodilation

Recurrent airway obstruction (RAO) is a well-known respiratory disease in horses, presenting itself with an acute onset of symptoms, which are the result of a bronchiolitis when susceptible horses are placed in a dusty environment. Inflammatory mediators are released during both the innate and adaptive immunity.
Allergens and inflammatory agents from different origins stimulate various cell types, and the following inflammatory response ultimately leads towards exacerbations of equine RAO. These agents are either part of an environmental (organic stable dust) challenge or are products from the inflammatory cascade itself. For example, the alveolar macrophage can be stimulated by substances found in hay dust solution, or by inflammatory mediators produced by the macrophage itself, or by other resident cells. The inflammatory cascade therefore amplifies itself through the actions of the mediators produced. External stimuli bind to the cells of the innate immune system, subsequently activating intracellular signalling pathways such as NFκB, which then leads to the formation of several pro- and anti-inflammatory cytokines and chemokines. Formation and secretion of TNF-α and IL-1β are sufficient to induce a secondary cascade involving, amongst others, a plethora of enzymes, including cyclooxygenases (COX-2) and lipoxygenases (LOX), catalyzing the increased signalling of prostaglandins, leukotrienes and iNOS. […]