The release of biologically active secretin-like immunoreactivity into duodenal lumen of dogs.

1. Immunoreactive secretin in the duodenal contents was determined in four conscious and four anaesthetized dogs in which hydrochloric acid (0.1 N) was infused into the duodenum at 2.2 ml./min. In the conscious dogs, immunoreactive secretin concentration in duodenal juice increased from 5-7 to 40-60 ng/ml. after infusion of HCl. In anaesthetized dogs, luminal immunoreactive secretin concentration increased from 2-3 to 12-16 ng/ml. after acid infusion. In both groups of dogs, a 20- to 30-fold increase in the total output of luminal immunoreactive secretin was observed. 2. Duodenal juice collected from anaesthetized dogs after diversion of both bile and exocrine pancreatic secretion was found to be the only source of luminal immunoreactive secretin. No immunoreactive secretin was found in either bile or pancreatic juice. 3. Gel filtration of the duodenal juice on a Sephadex G-50 column indicated that the immunoreactive secretin-like material in the duodenal juice possesses a molecular size similar to that of natural porcine secretin. 4. Immunoreactive secretin was partially purified from dog duodenal juice by chromatography on a SP-Sephadex column and found to be capable of stimulating pancreatic bicarbonate and water secretion in dogs.