Similar acid stimulatory potencies of synthetic human big and little gastrins in man.

A newly synthesized human big gastrin (G34) that was prepared according to the revised structure and that contained less than 3% oxidized methionine residues was compared with synthetic human little gastrin (G17) for acid-stimulating activity and clearance in human subjects. Prolonged infusions of each type of gastrin revealed that the time required to approach stable plasma concentrations was much longer for G34 than for G17. The time course of plasma gastrin concentration could be described by one-compartment models with half-lives of 44 min for G34 and 8 min for G17. After rapid intravenous infusion, G34 produced a much larger total acid response than did an equimolar dose of G17, and the responses were directly proportional to the integrated plasma gastrin increments. During the third hour of prolonged intravenous infusions of G34 and G17, the exogenous dosage of G34 required to produce the same blood concentration of gastrin was only one-fourth that of G17. Equivalent blood concentrations of G34 and G17 were associated with similar rates of acid secretion. These results suggest that G34 is more potent than has been thought, that it has an activity similar to that of G17 and that it must not be ignored in estimating total acid-stimulating activity of circulating gastrins. The measurement of total carboxyl-terminal immunoreactive gastrin can produce a good estimate of total acid-stimulating activity.