HRH1 and asthma: Emerging evidence has demonstrated that prolonged administration of LABAs increases the risk of asthma-associated mortality (6) or can seriously exacerbate asthmatic symptoms (8), possibly due to increased bronchial hyper-responsiveness (7) and bronchodilator and broncho-protection tolerance (9–11) The β2AR, fenoterol, induces the upregulation of G-protein-coupled neurokinin receptors and H1 histamine receptors in ASMCs (18,19) This suggests that β2AR may lead to increased bronchial responsiveness and bronchodilator tolerance by upregulating the expression of G-protein-coupled receptors.