Isolation and characterisation of prolactin-releasing peptide in chicks and its effect on prolactin release and feeding behaviour.

Prolactin (PRL)-releasing peptides (PrRP) have been identified in mammals, amphibians and fishes, and these animals have several PrRPs that consist of different numbers of amino acids such as 20, 31 and 37. In the present study, we identified the cDNA encoding chicken prepro-PrRP, which can generate putative PrRPs, and cloned and sequenced it. Sequences for the coding region suggested the occurrence of putative PrRPs of 20, 31 and 32 amino acid residues. The amino acid sequence of chicken PrRP20 showed 100%, 95% and 70% identity with those of PrRP20s from teleosts, Xenopus laevis and mammals, respectively. On the other hand, chicken PrRP31 showed approximately 90% and 52-55% homology to PrRP31s of X. laevis and mammals, respectively. Native chicken PrRPs were purified from an acid extract of chick brain by a Sep-Pak C18 cartridge (Waters Corp., Milford, MA, USA), affinity chromatography using anti-salmon PrRP serum, and reverse phase high-performance liquid chromatography (HPLC) on an ODS-120T column (TOSOH, Tokyo, Japan). The existence of chicken PrRP20 and PrRP31 in the brain was demonstrated by comparing them with the synthetic peptides using HPLC and matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry. Chicken PrRP31 increased plasma PRL concentration when administered peripherally, whereas central administration decreased the concentration, suggesting that chicken PrRP31 has a distinct effect on PRL secretion between tissues in chicks. On the other hand, plasma growth hormone concentration decreased with both peripheral and central administrations of chicken PrRP31. Furthermore, central administration of chicken PrRP31 increased food intake in chicks compared to those observed in mammals and fishes. Taken together with the results indicating that chicken PrRP20 did not show endocrine and behavioural effects, we showed that chicken PrRP has a similar amino acid sequence to teleosts, Xenopus laevis and mammals, although the actions were variable among vertebrates.