Atrial-natriuretic peptide
Atrial Natriuretic Peptide (ANP) (also called atrial natriuretic factor and atrial natriuretic hormone) is a vasodilator and a hormone. It is produced by the brain in response to increased blood pressure.  It inhibits renin, an enzyme produced by the juxtaglomerular apparatus.  This causes you to secrete more salt and water.