Guanylin is a 15 amino acid peptide that is secreted by goblet cells in the colon.

Guanylin acts as an agonist of the guanylyl cyclase receptor GC-C and regulates electrolyte and water transport in intestinal and renal epithelia.

[2][3] Upon receptor binding, guanylin increases the intracellular concentration of cGMP, induces chloride secretion and decreases intestinal fluid absorption, ultimately causing diarrhoea.

[3] Researches have found that a loss in guanylin expression can lead to colorectal cancer due to guanylyl cyclase C's function as an intestinal tumor suppressor.

[6] This loss of expression then resulted in guanylyl cyclase C inhibition and the formation of tumors, therefore linking diet-induced obesity with colorectal cancer.