HCAR1 and idiopathic pulmonary fibrosis: To test its role in the regulation of fibroblast phenotype by extracellular lactate, we examined GPR‐81 expression in control and IPF fibroblasts under normoxic and hypoxic conditions and found that hypoxia increased GPR‐81 in both control and IPF fibroblasts (Figure 7a, upper and lower).