Bombesin ingestion stimulates epithelial digestive cell proliferation in suckling rats

The characterization of a bombesin-like peptide in the breast milk of some mammals might suggest that this peptide may influence, in part, the postnatal development of the digestive tract. To test this hypothesis, our experiments investigated whether oral administration of bombesin affects epithelial progenitor cell proliferation in digestive organs of suckling and weaned rats. Four series of pups were given bombesin diluted in milk (20 micrograms/kg, 3 times daily) or milk alone, for 5 days during either the first, second, third, or fourth week of life. Pups were killed after [3H]thymidine pulse labeling. DNA labeling and mitotic indices were estimated in the oxyntic, antral, colonic mucosae, and exocrine pancreas. In all tissues examined, oral bombesin significantly increased over control values the two cell proliferative parameters studied during the suckling period (P less than 0.05 to P less than 0.001). In bombesin-treated rats, maximal stimulation of these parameters occurred in the second week of life. This effect of oral bombesin on the cell kinetics disappeared in all tissues after weaning. This study confirms the growth-promoting effect of bombesin observed on the digestive system of the neonatal rat after subcutaneous administration of the peptide and shows that bombesin, when given orally to suckling rats, is sufficiently resistant to proteolysis to enable it to exert a stimulatory effect on digestive cell proliferation. However, our findings as such do not prove that milk bombesin-like peptide has a physiological influence on the developing gastrointestinal tract and pancreas.