The gastrointestinal tract is the largest endocrine organ and holds a special place in endocrinology since the concept of blood-borne communication between cells was first established through experiments on the gut. Gut peptide hormones and neurotransmitters regulate the complex processes of digestion, motility, epithelial growth, and integrity. Investigation of this complex endocrine organ has depended on the development of sensitive and specific radioimmunoassay. Radioimmunoassays have also increased our understanding of pathophysiological processes affecting the gut, including rare gastroenteropancreatic neuroendocrine tumours. The object of this chapter is to describe the techniques used in the radioimmunoassay of common gastrointestinal hormones.
