Nature of the gastric acid-gastrin feedback loop in the fetal sheep.

1. The neonates of sheep and other species have a decreased gastric acid secretion but an elevated plasma gastrin concentration. 2. Since low gastric acid secretion is a stimulus for gastrin release in mature animals the present study examined whether the relative hypochlorhydria in the sheep fetus was sustaining the hypergastrinaemia. 3. Fetal plasma gastrin was measured following fetal gastric acidification (pentagastrin infusion) and gastric neutralization (parietal cell blockade with the proton pump inhibitor omeprazole) in chronically cannulated fetal sheep from 101 days until term (145 days). 4. Acutely raising gastric pH with omeprazole increased plasma gastrin in the mature sheep. However, in the fetus increasing the pH with omeprazole or decreasing pH with pentagastrin had no effect on fetal plasma gastrin. This was true for fetuses from all age groups. 5. The results indicate that the gastric acid-gastrin feedback loop is not functional in the fetus and that the hypergastrinaemia at birth is therefore not the result of the relative hypochlorhydria. 6. The time after birth when the gastric acid-gastrin feedback loop matures remains to be determined.