The existence of a delayed inhibition of the secretion of protein by the rat pancreas after intraduodenal injection of oleic acid has been confirmed. 1. This phenomenon is not dependent on the presence or absence of bile or pancreatic juice in the intestine. 2. The action of oleic acid is not a pathological phenomenon due to lesions of the gut mucosa because isotonic solutions of Na oleate dispersed into polysorbate 80 or olive oil (rich in oleic acid) plus pancreatic juice have the same effect. 3. Fatty acids must be free or saponified but not esterified in the form of triglycerides. Triglycerides are only effective if pancreatic juice is simultaneously reintroduced into the duodenum. 4. Oleic acid (C18 mono?ne) is more efficient than caprylic acid (C8) and butyric acid (C4) is ineffective. The effect of chain length in releasing the inhibitory factor is therefore approximately the same as in CCK-PZ release. 5. Intraduodenal infusion of hypertonic glucose solution does not inhibit pancreatic protein secretion indicating that release of enteroglucagon is probably not responsible for the inhibition. The inhibitory action of hypertonic NaCl solution is not explained.
Animals Butyrates