First, we investigated the classical ERs, ERα, and ERβ, which predominantly act as transcription factors regulating gene expression, and the novel G-protein-coupled receptor, GPER, which mediates rapid, non-genomic effects of oestrogen.12 ERα expression was mainly localized to smooth muscle in the pulmonary arteries from control and PAH patients. Here, GPER1 is linked to pulmonary arterial hypertension.