Hydroxycarboxylic acid receptor 1

Hydroxycarboxylic acid receptor 1 (HCA1), formerly known as G protein-coupled receptor 81 (GPR81), is a protein that in humans is encoded by the "HCAR1" gene. HCA1, like the other hydroxycarboxylic acid receptors HCA2 and HCA3, is a G protein-coupled receptor (GPCR). The primary endogenous agonist of HCA1 is lactic acid (and its conjugate base, lactate).
Lactate activates HCA1, which in turn inhibits lipolysis in fat cells.