Roles of gastrin and somatostatin in the regulation of gastric acid secretion in the fetal rabbit

In adult gastric epithelium, gastrin and somatostatin regulate parietal cell acid secretion; however, their expression and function in the fetus are largely unknown. We defined the developmental expression of gastrin and somatostatin in the fetal rabbit stomach and determined their effects on fetal acid secretion. To define peptide expression, fetuses from 12 time-mated New Zealand white rabbit does were analyzed at successive ages during the third trimester (term is 31 days). Peptides were extracted from fetal gastric tissue by boiling in water and then in acetic acid. Amidated gastrin and somatostatin levels were measured by radioimmunoassay using antisera 1296 for gastrin and 8402 for somatostatin. To determine the effects of gastrin and somatostatin, pentagastrin (64 microg/kg/hr) or octreotide (35 microg/kg/hr) were infused intravenously in conscious pregnant rabbits at 28 days of gestation for 3 hr. Fetuses (n = 45) were harvested and gastric acid was titrated with 0.02 N NaOH. Gastrin and somatostatin tissue content were 12 +/- 3 and 51 +/- 6 pmol/g at gestational day 20, respectively, and increased to 146 +/- 10 and 162 +/- 5 pmole/g by day 30 (P < 0.05). Between days 24 and 26, when gastric acid was first detectable, the molar ratio of somatostatin to gastrin decreased from 5.0 +/- 1.0 to 1.1 +/- 0.1 (P < 0.05). Fetal gastric acid content (micromole) was 28.5 +/- 1.7 in controls, 27.5 +/- 1.9 with pentagastrin treatment, and 15.8 +/- 1.4 micromole with octreotide (P < 0.05). In summary, 1) In fetal gastric tissue, gastrin increased 12-fold and somatostatin increased 3-fold between days 20 and 30 of gestation. 2) The decreased ratio of somatostatin to gastrin between days 24 and 26 of gestation coincides with the onset of fetal gastric acid secretion in the fetal rabbit. 3) Maternal administration of octreotide inhibited fetal gastric acid content; however, pentagastrin had no effect. We conclude that, in the fetal rabbit stomach, the relative expression of gastrin and somatostatin may regulate the onset of parietal cell acid secretion.