The half‐life of exogenous gastrin in the circulation

1. A method of gastrin bio‐assay is described which can be used on as little as 30 ng synthetic human gastrin I at a minimum concentration of 2·5 ng/ml. 2. Pentagastrin or synthetic human gastrin I added to cat plasma can be stored on ice or at 4° C, for periods up to 27 hr without apparent loss of gastrin activity. 3. Between 1½ and 13 min after the rapid I.V. injection of pentagastrin in the anaesthetized cat and between 1½ and 15 min after the injection of synthetic human gastrin I, there is a rapid reduction of the gastrin concentration in the arterial plasma. The data relating log 10 gastrin concentration in arterial plasma with time can be fitted by a single term. 4. Studies in vitro show that over the periods of time involved in the in vivo studies, both pentagastrin and synthetic human gastrin I are stable in cat plasma at 37° C in concentrations which occurred in the circulating plasma. 5. The half‐life of pentagastrin in the circulating arterial plasma of the anaesthetized cat is 1·50 min ( S.E. ± 0·08) and the half‐life of synthetic human gastrin I is 2·65 min ( S.E. ± 0·09).