The interaction of secretin and stimulants of gastric acid secretion in anaesthetized cats.

1. In fasting anaesthetized cats in which the pylorus and common bile duct were occluded, acid secretion in response to caerulein, desulphated caerulein, histamine and N methyl histamine given singly and combined with Boots secretin 4 C.H.R. u./kg hr has been studied. 2. Eight separate estimates of the calculated maximal response of acid (four acid stimulants given with and without secretin) did not differ significantly from one another. In the presence of secretin the E.D.50 of each acid stimulant was lowered. 3. Outputs of acid in response to the smallest doses of desulphated caerulein, histamine and N methyl histamine increased significantly when secretin was infused (P less than 0-05). 4. On a weight basis caerulein was 23, 474 and 95 times more potent than desulphated caerulein, histamine and N methyl histamine respectively. 5. When secretin was infused simultaneously caerulein was 8, 171 and 165 times more potent than desulphated caerulein, histamine and N methyl histamine respectively. 6. N methyl histamine was 5-6 times more potent than histamine on a weight basis when infused on its own; and 1-16 times more potent than histamine when given in the presence of secretin.