Ontogeny of gastric acidity in the ovine fetus.

Hypoacidity and hypergastrinaemia have been reported in the newborn human. However, little is known about in utero gastric acid secretion, and the relationship to fetal plasma gastrin levels. The longitudinal pattern of development of basal and stimulated gastric acid secretion in the non-anaesthetized fetal sheep has been studied during the last 45 days of gestation. Fetuses had cannulae inserted into the jugular vein, carotid artery and stomach. Gastric juice and blood was sampled daily from 101 days gestation until birth (145 days). Intermittent basal acid secretion began between 120 and 133 days of gestation. These fluctuations in gastric juice pH continued until birth. Overall there was a decline in gastric pH from 7.5 +/- 0.2 (SEM), for fetuses 101-105 days to 4.3 +/- 0.5 by 131-135 days. Mean fetal plasma gastrin was higher than maternal levels after 111-115 days but no correlation between fetal plasma gastrin levels and gastric pH could be demonstrated. Pentagastrin and histamine infusion did not stimulate acid secretion in fetuses younger than 115 days. After this age the fetuses became responsive to both pentagastrin and histamine. In contrast, cholinergic stimulation, using bethanechol, did not stimulate acid production until 10 to 15 days later, suggesting a hierarchy in the development of the control of acid secretion in the fetus. The lack of response to endogenous gastrin and the hierarchy in the control of acid secretion suggest either a lack of receptors on the parietal cell or the presence of an inhibitor of acid secretion. These studies are relevant to human physiology since the present findings show that the sheep and human have a similar gastrin/acid profile at birth.