Bombesin analogs: effects on thermoregulation and glucose metabolism

Twenty-six peptides, analogs of bombesin (BNa) and gastrin releasing peptide (GRP), have been synthesized by the solid phase method. The synthetic peptides were purified by ion exchange and partition chromatography and shown to be homogenous under various conditions on RP-HPLC. They were further characterized by TLC, amino acid analysis and optical rotation. These peptides have been administered IC to rats and their effects on thermoregulation and glucoregulation have been compared to those of the two natural peptides: frog skin bombesin (BNa) and GRP. Their structure activity relationship is also discussed. The minimum essential residues required for full potency of bombesin-like effects is represented by an acetylated C-terminal 8-peptide fragment, where in position 7 of this peptide an L-amino acid such as alanine, histidine or glutamine, or the D-glutamine residue can be introduced. Modification of the tryptophan [8] and histidine [12] residues by alanine abolished the biological potency of those peptides. Analogs with a free N-terminus were found to express little, but significant, activity, thus indicating that blocked N-terminus is necessary for maximal response. [Ac-Ala7, DAla11]-bombesin (7--14) and [Ac-DGln7 DAla11]-bombesin (7--14) were found to be more potent than bombesin, whereas [Ac-DAla7, DAla11]-bombesin or [Ac-DAla7, DAla11] bombesin N-methylamide were found to have 10 and 1% of bombesin potency, respectively.