Uvnas,1 in the 1940's was the first to note a decreasing response to repeated stimulation with crude gastrin extracts, but this effect was thought to be due to a contaminating inhibitory factor. The inhibition of gastric acid secretion by extracts containing gastrin was first demonstrated clearly by Gillespie and Grossman2 in 1963 and confirmed by Gregory and Tracy3 (1964) using a highly purified preparation. The mechanism of this dual action of gastrin, also possessed by the synthetic pentapeptide has not been adequately explained. The ability of a substance to act in a stimulatory capacity in small doses and to inhibit when given in larger amounts is, however, well recognized, eg, acetylcholine and nicotine. In the case of gastrin, this dual action has been thought of little importance in the physiologic mechanisms responsible for controlling its release and activity in the normal state.
Most studies2,4-9 on gastrin