Changes in basal- and
pentagastrin-stimulated gastric acid,
pepsin secretion as well as gastric mucosal
histidine decarboxylase activity were examined in 4- to 21-month-old pyloric ligated Fischer-344 rats. In addition, serum
gastrin levels, gastric mucosal
DNA, and
RNA content were determined in these rats. The results revealed that whereas
acid secretion decreased progressively with age,
pepsin output increased between 4 and 14 months of age and then decreased sharply. Serum
gastrin levels decreased progressively with age, and 3 h of
pyloric obstruction produced no apparent change in serum
gastrin levels in any of the age groups. Gastric mucosal weight,
DNA, and
RNA content in 4-month-old rats were not significantly different from those of 14-month-old animals. However, in 21-month-old rats, each of these values were found to be significantly lower than in their 4- or 14-month-old counterparts. A single injection of
pentagastrin (250 micrograms/kg) significantly stimulated
acid and
pepsin secretion (45-52%) in 4-month-old rats, but not in 14- and 21-month-old animals, when compared with the corresponding saline-injected controls. Gastric mucosal
histidine decarboxylase activity increased steadily between 4 and 21 months of age.
Pentagastrin caused a significant 78% stimulation in
histidine decarboxylase activity in 4-month-old rats, but had no effect on the
enzyme activity in 14-month-old animals, when compared with the corresponding saline-injected controls. However, in 21-month-old rats,
pentagastrin inhibited
histidine decarboxylase activity by 55% when compared with the saline-injected controls. It is concluded that a) aging decreases capacity of the gastric mucosa to secrete
acid and
pepsin, b) in aged rats, decreased
acid and
pepsin output could in part be attributed to mucosal
atrophy; c) responsiveness of the gastric mucosa to
pentagastrin decreases with age; and d) in aged animals, gastric acid secretion is not regulated by
histamine.