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Abstract
A bioassay sensitive to gastrin (G 1–17) in physiological concentrations and suitable for testing of biological activity of minor amounts of radioiodinated gastrin is reported. G 1–17 was iodinated by a gentle Iodo-gen method and purified to high specific activity (1900 Ci/mmol). Totally isolated vascularly perfused rat stomachs were prepared and stimulated by graded amounts of G 1–17. Gastrin 'dose'-dependently increased the acid output from 5.7 ± 1.0μeq/40min (basal) to a maximum of 58.8 ± 10.0 μeq/40 min at a concentration of 520pmol/l in the vascular perfusate. The lowest G 1–17 concentration that significantly increased the acid output from the basal value was 65 pmol/1, corresponding to a dose of 17.5 ng/stomach-hour. 125I-G 1–17 also increased the acid output significantly at this threshold dose. The amount of lactic acid enzymatically determined in the luminal perfusate was negligible, indicating a true parietal cell stimulation. Accordingly, a very sensitive bioassay for gastrin, suitable for testing of biological activity of G 1–17 and 125I-G 1–17, is described. Significant acid responses were obtained with physiological concentrations of gastrin, requiring less than 100 ng of hormone and labelled hormone, respectively, to show biological activity.