VIPR1 and pulmonary arterial hypertension: Interestingly, vasoactive intestinal peptide receptor 1 (VIPR1) (Table 2), a marker for lung specific endothelial cells know to be downregulated in PAH patients [33], was greatly reduced in CECs (log2FC = -4.21, pAdj = 3.09E-05) and in LECs (log2FC = -0.7582 pAdj = 0.21).