Pitfalls of the continuous histamine test for gastric secretory inhibition

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Abstract
Dogs with Heidenhain pouches were given histamine at a constant rate for 6 hours or longer. Output of HCl from the pouch was measured every half hour, and each secretory response was divided into control and test phases, according to the procedure of the continuous histamine test. However, no inhibitory factor was introduced. In 32 experiments the rate of HCl output reached a stable level during the control phase, but many responses failed to show stability throughout the test phase. Frequently, there was a pronounced drop in rate of HCl output below the pre-established control level. With the continuous histamine test, it is sometimes assumed that any appreciable drop in rate of HCl output during the test phase is attributable to the factor being tested and that it represents inhibition of the histamine-induced response. The results of the present study illustrate that this premise may be invalid under certain conditions. If control studies are not performed with the continuous histamine test, spontaneous drops in rate of HCl output are apt to be misinterpreted as evidence of inhibition. Note: (With the Technical Assistance of S. Mehta) Submitted on September 8, 1958