Immunoreactive secretin in gastrointestinal mucosa of several mammalian species.

Immunoreactive secretin in hydrochloric acid extracts is relatively constant in the duodenum and proximal jejunum of pig and dog (3 microgram per g), but peaks in the distal duodenum of guinea pig (1 microgram per g), no secretin being detectable in the ileum of these species. Secretin is relatively constant throughout the small intestine of the rat and rabbit (0.4 to 0.1 microgram per g). Sephadex gel filtration patterns of all species and throughout the gastrointestinal mucosa revealed primarily a single peak with elution characteristics identical with that of purified or synthetic porcine secretin. The "big" secretin prominent in Boots secretin may be an alteration product perhaps attributable to chemicals used to stabilize the preparation. The "intermediate secretin" described by others has not been detected. It is concluded that in a variety of mammalian species most of the immunoreactive secretin extractable from the intestinal tract lies distal to the proximal duodenum and is not distinguishable from duodenal secretin in terms of molecular size.