EXPERIMENTAL STUDIES ON SERUM GASTRIN LEVELS AND IMMUNOREACTIVE GASTRIN CONCENTRATIONS IN THE GASTROINTESTINAL MUCOSA OF RATS: (1) Changes Following Fetal and Postnatal Growing

Changes of serum gastrin levels and immunoreactive gastrin (IRG) concentrations of antral and upper intestinal mucosa in the course of growing rats were examined. The results obtained were as follows; 1) Serum gastrin levels were already detectable in rats at one week after birth, and thereafterincreased to 199pg/ml temporarily at two weeks after birth. 2) Intra-tissue IRG and G cells were only of a trace amount even in the antral mucosa during the fetal period. However, there was a definite increase of them in the antral mucosa both at the commencement of suckling as well as at the commencement of weaning and feeding. 3) In the duodenum, jejunum and corpus of the stomach, the value of IRG showed a temporary increase also at two weeks after birth when serum gastrin levels increased rapidly. 4) The molecular form in the antral IRG was mainly the so-called little gastrin (LG, G-17)throughout the fetal and adult ages. However, the molecular form in duodenal and jejunal IRG were mainly LG in the fetal period and thereafter it became big gastrin (BG, G-34) which increased gradually in parallel with aging. From these observations, it was suggested that feeding played an important physiological role not only in the production but also in release of gastrin with special regards to its influence on the metabolism of gastrin.