Once isolated peptides have been sequenced, pure synthetic peptide can be produced and administered by intravenous infusion to determine its physiological role as a circulating hormone. Gastrointestinal actions such as enzyme release or motility, or systemic effects such as vasodilatation, may be seen. Such effects are sometimes found only at markedly supraphysiological doses, suggesting that the peptides may be most important as paracrine agents, controlling gastrointestinal function locally where they will reach much higher concentrations than in the circulation.
