Maturational increases and decreases in acid secretion in the rat

We compared basal acid output (BAO) and maximally stimulated acid output (MAO) in 15-, 30-, and 100-day-old anesthetized rats. At each age we measured BAO and MAO in response to six different stimuli, pentagastrin (120 micrograms X kg-1 X h-1), bethanechol (1 mg X kg-1 X h-1), histamine (8 mg X kg-1 X h-1), the H2-receptor agonist impromidine (0.9 mumol X kg-1 X h-1), hypothermia (30 +/- 2 degrees C core temperature), and pyloric ligation, and we determined H+ output by continuous perfusion of the gastric lumen of anesthetized rats. Both weight-adjusted and absolute BAO were significantly greater in 30-day-old rats than in 15- or 100-day-old rats. Although 30-day-old rats had only one-fourth the fundic mass of 100-day-old rats, they could secrete two to three times more H+ per hour. These differences in MAO persisted even after subtracting BAO. Anatomic data indicate that these age-related changes do not correspond to changes in mucosal mass or parietal cell mass.