Mechanisms of protein activation of the intestinal phase of gastric secretion.
To determine if the secretory response to protein in the gut is due to direct effects of absorbed amino acids on the parietal cells, to hormonal effects, or to a combination of both, Heidenhain pouch secretion and plasma amino nitrogen levels were measured during enteral infusions of casein or liver extract, as well as during intravenous infusions of amino acids, in three dogs with and three dogs without portacaval transposition. In the dogs without portacaval transposition, gastric secretory responses were slight and did not differ significantly; secretory responses were seen only during infusions in which elevations of plasma amino nitrogen values occurred. In dogs with portacaval transposition, secretory responses to both casein and liver extract were significantly higher (P less than 0.02) than was the response to intravenous amino acids, while plasma amino nitrogen levels rose to virtually identical levels during all three kinds of infusion. These data support the hypothesis that absorbed amino acids contribute to the intestinal phase of gastric secretion. The finding that casein and liver extract in the gut evoked greater gastric secretion responses than did intravenous amino acids, even though increases in plasma amino nitrogen levels were similar, suggests that the intestinal phase results form the combined effects of absorbed amino acids and hormonal influences rather than from the effects of amino acids alone.