Bombesin differentially affects gastric emptying in suckling, weanling and adult rats

The gastric effect of bombesin, a homolog of the mammalian peptide found in breast milk, was studied in suckling, weanling and adult rats (11, 30 and 90 days old, respectively). Control gastric emptying was not different in the three age groups. When bombesin was given orogastrically in a saline vehicle, 30 min before a nonabsorbable radiolabeled marker (used to assess gastric emptying), a significant and dose-related inhibitory effect was observed in sucklings. In contrast to the data with orogastric peptide in saline, when bombesin was given orogastrically in rat milk 30 min before the marker, there was no effect on gastric emptying in sucklings. Inhibition of gastric emptying was again demonstrated in the sucklings when bombesin (0.6-30 micrograms) was given with an artificial rat milk substitute 30 min before the marker. In contrast, orogastric bombesin in rat milk or rat milk substitute had no effect on gastric emptying in weanlings or adults. While s.c. bombesin in saline did not alter gastric emptying in sucklings, s.c. administration of the peptide produced a significant and dose-related increase in gastric emptying in both weanlings and adults. These results support the concept that milk-borne peptides, such as gastrin releasing peptide, may be involved in regulation of gastric function in suckling rats.