Alpha-1 adrenergic receptors are G protein-coupled receptors for catecholamines that signal through the G(q) family of G proteins, including G(q) and G(11). Upon activation, they stimulate the phosphatidylinositol-calcium second messenger pathway, leading to calcium release from intracellular stores and activation of protein kinase C (PubMed:7746284). ADRA1D binds the catecholamine ligands norepinephrine and epinephrine (PubMed:7815325, PubMed:8024574, PubMed:8183249). {ECO:0000269|PubMed:7746284, ECO:0000269|PubMed:7815325, ECO:0000269|PubMed:8024574, ECO:0000269|PubMed:8183249}. This is the function of ADRA1D (adrenoceptor alpha 1D, Ensembl gene identifier ENSG00000171873).