Ontogeny of gastric mucosal muscarinic receptor and sensitivity to carbachol.

Development of the muscarinic cholinergic receptor and sensitivity of oxyntic gland mucosa to a muscarinic agonist were studied in rats of various ages. The gastric lumen of the fetal rat at the 20th day of gestation contained a statistically significant amount of basal pepsin, which increased log linearly over the first 30 days of life. Carbachol was effective in stimulating the secretion of pepsin as early as 12 h after birth. Basal acid could be measured in the gastric lumen 12 h after birth. The secretion of basal acid increased log linearly over the first 30 days of life. Carbachol was an effective secretagogue even in the fetal rat. The density of the muscarinic cholinergic receptor of the adult rat oxyntic gland mucosa was 99.3 fmol/mg protein with an apparent equilibrium dissociation constant for quinuclidinyl benzilate of 0.40 nM. The receptor was well developed even in the fetal rat, which bound 79.6 fmol/mg protein with an apparent equilibrium dissociation constant of 0.26 nM. Except for immediately after birth, receptor density was maintained between 70 and 90% of the adult level over the first 30 days of life. These results suggest that cholinergic regulation of gastric acid and pepsin secretion is probably functional by either late gestation or at least immediately after birth.