[Secretion radioimmunoassay, physiology and pathophysiology in man]

Production of antibodies to secretin for radioimmunoassay is straightforward. Secretion is iodinated by weak oxydation with lactoperoxydase and subsequent purification by ionexchange chromatography (Sephadex C25). The specific activity of fresh label is between 650 and 900 mCi . mol-6. The label is highly purified and may be used in radioimmunoassay for several months. In order to eliminate plasma interference sepharose-beads with covalently coupled secretin antibodies are used to produce secretin-free standard plasma samples. Delay in the separation of plasma from fresh blood samples can lead to erronous results, even to falsely elevated secretin levels.--Duodental acidification only leads to physiological increases of secretin plasma levels. This may happen by intraduodenal instillation of acid, or by an acidic oral drink, or to a lesser extent after a meal. Secretin is distributed throughout the plasmavolume and has a short halflife of around 3 minutes. Impaired release of secretion is found in children with coeliac disease. The role of secretin in peptic ulcer however is not clear. Chronic pancreatitis and renal insufficiency are without effect on plasma secretin levels.