In this study, we report the purification, cDNA cloning, and characterization of the novel growth hormone-releasing peptide, ghrelin, in the chicken (Gallus gallus). Chicken ghrelin is composed of 26 amino acids (GSSFLSPTYKNIQQQKDTRKPTARLH) and possesses 54% sequence identity with human ghrelin. The serine residue at position 3 (Ser(3)) is conserved between the chicken and mammalian species, as its acylation by either n-octanoic or n-decanoic acid. Chicken ghrelin mRNA is predominantly expressed in the stomach, where it is present in the proventriculus but absent in the gizzard. Using RT-PCR analysis, low levels of expression were also detectable in brain, lung, and intestine. Administration of chicken ghrelin increases plasma GH levels in both rats and chicks, with a potency similar to that of rat or human ghrelin. In addition, chicken ghrelin also increases plasma corticosterone levels in growing chicks at a lower dose than in mammals. The present results indicate that the stimulatory effect of ghrelin on GH secretion is evolutionarily conserved, whereas its effect on adrenal function seems to be unique in the chicken.

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This paper reports the results of in vivo and in vitro experiments on the feedback effects of corticosterone on the hypothalamo-pituitary-adrenal axis in embryos at day 18 of incubation and in 9-day-old chickens. In vivo, a significant negative feedback was detected on the levels of corticotropin-releasing factor (CRF) precursor (proCRF) mRNA and on the plasma concentration of corticosterone, two hours after a single intravenous injection with 40 µg corticosterone. In contrast, the levels of CRF peptide in the hypothalamic area, the CRF receptor type 1 (CRF-R1) mRNA and pro-opiomelanocortin (POMC) mRNA levels in the pituitary were not affected by the in vivo administration of corticosterone. In vitro, incubation with 1 µM corticosterone did not affect the CRF-R1 mRNA levels in the pituitary, but significant feedback inhibition was observed on the POMC mRNA levels. These in vitro effects were the same at the two ages studied. The in vitro feedback effect on the proCRF gene expression, however, differed with age. In 9-day-old animals a decrease in gene expression was observed which was not detectable in embryonic tissue at day 18 of the ontogeny.