Satiety and scratching; effects of bombesin-like peptides

Two novel amphibian peptides, [Ser7]litorin-like peptide (Ser-LIT) and [Ser7]bombesin-like peptide (Ser-BN), recently isolated from the skin of the South American frog Phyllomedusa sauvagei, are characterized by the occurrence of a Ser residue in place of His7 in the C-terminal tripeptide. For testing on food intake in fasted rats the peptides were injected intraperitoneally (i.p.) and intracerebroventricularly (i.c.v.) and their activity compared with that of bombesin (BN) and litorin (LIT). Ser-LIT was completely ineffective on food intake while Ser-BN was about ten times less potent than LIT by i.p. injection; given i.c.v., Ser-BN inhibited food intake in the first 15 min after injection but its effect faded within 60 min. The i.c.v. administration of both [Ser7]-substituted peptides, elicited intense scratching with a potency equal to or higher than that of BN or LIT. The existence of two different kinds of receptors for BN-like peptides may be hypothesized: the first, specific for the C-terminal tripeptide sequence, is apparently involved in the inhibition of feeding; the second, responsible for the stimulating activity on the urinary bladder and for scratching, shows higher affinity for the N-terminal portion of the biological active sequence.