Radioimmunoassay of Plasma Gastric Inhibitory Polypeptide (GIP), Release of GIP after a Test Meal and Duodenal Infusion of Bile, and Immunoreactive Plasma GIP Components in Man

Abstract

A sensitive, precise and specific radioimmunoassay method for measuring plasma gastric inhibitory polypeptide (GIP) is described. The present assay system, using a label purified on a Sephadex G-15 and a SP Sephadex C-25 column as well as careful corrections for nonspecific plasma effects, allows measurements of fasting plasma GIP in the lower pmol/l range and the significant rise in plasma GIP subsequent to a test meal and doudenal infusion of cattle bile. Apparent immunoreactive fasting plasma GIP was eluted from a Sephadex G-50 Fine column in 1 peak probably representing plasma GIP bound to plasma proteins and nonspecific plasma effects. Apparent immunoreactive meal-stimulated plasma GIP was eluted from a Sephadex G-50 Fine column in 2 large and 1 diminutive peak. The 1st peak probably represents plasma GIP bound to plasma proteins and nonspecific plasma effects, the almost negligible 2nd peak probably represents big GIP with MW of some 9000 and the 3rd and major peak, little GIP with a MW of about 5000.