Rapid extraction of secretin from plasma by XAD-2 resin and its application in the radioimmunoassay of secretin

A simple and rapid method for extraction of plasma secretin has been developed. In this method plasma was allowed to percolate through a XAD-2 resin (a copolymer of styrene and divinylbenzene) column, and secretin was eluted by acid methanol in good yield. The column extract showed little interference in the radioimmunoassay as evidenced by the superimposability of the standard curve prepared in the presence of the column extract to that prepared in the buffer alone. Furthermore, the bound-to-total ratios of radioactive secretin were not affected by the presence of column extracts of secretin-free plasma from different subjects. Using the method described, we were able to detect significant increases in plasma secretin levels in both dogs and humans following intraduodenal infusion of 0.05 n hydrochloric acid in much smaller quantities than those reported in the literature.