GH-releasing activity of Hexarelin, a new growth hormone releasing peptide, in infant and adult rats.

In recent years several synthetic peptides have been shown to be active in inducing GH secretion in different mammalian species. Among them GHRP-6, GHRP-1 and GHRP-2 have demonstrated high effectiveness and high selectivity in stimulating GH release. In the present paper we report studies on the GH-secreting properties of a GHRP analog in which Trp was substituted with the chemically more stable 2-Methyl-Trp. In studies performed in conscious 10-day old rats, the hexapeptide Hexarelin (His-D-2Me-Trp-Ala-Trp-D-Phe-Lys-NH2) resulted very active in stimulating GH secretion. In anesthetized adult male rats, i.v. administration of GHRP-6 or Hexarelin elicited prompt GH release with peak GH levels occurring within 10 min At all the doses tested, the 2 peptides possessed similar effectiveness in stimulating GH release. Hexarelin given s.c. elicited a long-lasting GH release and was slightly more effective than GHRP-6. In conclusion, these findings indicate that Hexarelin is a highly effective GH releaser and might represent a valuable diagnostic and/or therapeutic tool in clinical practice.