Ontogeny of gastric secretion in the rat. Ultrastructural changes in relation to secretory changes

Basal and stimulated gastric acid secretion are three to four times greater in the juvenile (30-day-old) rat than in the adult (100-day-old) rat, even though the parietal cell mass is greater in the adult. In this study we examined the possibility that the H+ secretory activity of individual parietal cells is greater in juvenile rats. To do this we used quantitative measures of secretory canaliculi and tubulovesicles as indirect measures of parietal cell H+ secretory activity. We determined that, under the experimental conditions used, the morphologic measures bear a sufficiently close linear relationship to total gastric H+ output to justify their use. We then found that when individual parietal cells from 30-day-old rats are compared quantitatively with those from 100-day-old rats, each cell from the younger rats has, on average, significantly more of the morphologic characteristics associated with higher H+ output. We inferred that individual parietal cells of 30-day-old rats, on average, may be secreting more H+ than corresponding cells of 100-day-old rats under comparable stimulation conditions.