Somatostatin 28 arises from the posttranslational cleavage of prosomatostatin, which in turn is derived from a large precursor, preprosomatostatin. Somatostatin 28 has been found in the central and peripheral nervous system and in the gastrointestinal (GI) tract where it acts as a somatostatin receptor agonist. Som-28 can induce opposite biological effects, which suggests that Som-28, acting through distinct receptors, may function in the manner of several different neurotransmitters or neuromodulators.