The family of guanylin regulatory peptides, including guanylin and uroguanylin, are strongly expressed in intestinal mucosa and regulate intestinal fluid secretion during digestion. Guanylins are also involved in acid neutralization and the regulation of membrane-bound guanylate cyclase signaling molecules. Guanylin and uroguanylin are secreted primarily in the stomach, intestine, and colon. Guanylin is also detected in plasma. Guanylin is an endogenous activator of intestinal guanylate cyclase. It stimulates intestinal guanylate cyclase through the same receptor binding region as the heat-stable enterotoxins. Gut enterochromaffin cells synthesize guanylin to be a prohormone of 115 amino acids which is then is processed to the molecular form of 94 amino acids. This 10kDa form is found circulating in the blood.