To explore whether the integrated stress response of the ER occurs in parallel with MUC5AC hypersecretion in rats with COPD, expression levels of typical UPR proteins, such as p‐IRE1α, XBP‐1, GRP78 and ATF6, were determined by Western blotting in lung tissues. The gene discussed is MUC5AC; the disease is chronic obstructive pulmonary disease.