Secretin

The preparation of secretin has been described in a previous paper (1928). The method involved extraction of the duodenal mucosa with absolute alcohol and precipitation of the dissolved secretin by bile salts. It was based on two observations: (a ) secretin exists in the duodenal mucosa in an active condition, and (b ) the secretion of pancreatic juice is due primarily to the absorption of bile salts in the duodenum. The bile salt used in the precipitation of secretin was commercial sodium tauroglycocholate. Apparently many varieties of this commercial bile salt preparation exist depending on the type of bile from which it has been obtained. For this reason many experimenters have experienced difficulties in obtaining satisfactory yields of secretin by this method. The conditions under which pure taurocholic acid precipitates secretin from solution have been worked out, but since this bile acid is difficult to obtain the results are of small general interest. For these reasons the preparation of secretin by a method which requires no special reagents is described. The description is divided into three stages. At each of these stages the preparation may be left for some days without deterioration. (1) The duodenum and upper part of the jejunum (i. e. , 3 feet of gut from the pyloric sphincter) of the recently killed pig is used as the source of the secretin. The mucous membrane is scraped off within 3 hours of the death of the animal, ground up with sand, and extracted with a volume of ethyl alcohol equal to four times its weight. The mixture is well shaken, allowed to extract at room temperature for 30 minutes and then filtered. The clear filtrate, if kept in the dark in a cool place, retains its activity for several days. It may be observed that a solution of secretin containing bile pigment is destroyed rapidly by light.