Mucosal DNA Synthesis: A Short Term Index of the Trophic Action of Gastrin

Abstract

Gastrin has been shown to be an important trophic hormone for the gastric mucosa. In order to assess its role in the metabolism of other tissues and to determine whether other hormones and related substances affect the growth of gastrointestinal tissue, an assay was developed which measured in vitro DNA synthesis in small pieces of tissue. Rats were injected with 250 μg per kg of pentagastrin or with saline and killed at various times after injection. Small pieces of stomach, duodenum, ileum, and liver were removed and incubated for 30 min in tissue culture medium containing [3H]thymidine. DNA was extracted and the rate of DNA synthesis was determined by scintillation counting. In another set of experiments the dose of pentagastrin which gave maximal DNA synthesis was determined. Pentagastrin had no effect on DNA synthesis in the liver. In all other tissues studied maximal stimulation occurred 16 hr after injection of pentagastrin. At 16 hr, incorporation of thymidine in pentagastrin-injected animals was 275% of control for the stomach, 300% for the duodenum, and 480% for the ileum. In another series of studies histamine (20 mg per kg) had no effect on DNA synthesis. A dose-response study demonstrated that 250 μg per kg of pentagastrin was optimal for these effects on DNA synthesis. It made little difference whether the results were expressed on the basis of tissue wet weight or DNA content. This procedure offers a relatively rapid means of assessing the growth promoting potential of various substances on tissues of the gastrointestinal tract.