Analogues of human growth hormone-releasing hormone (1–30)-amide have been developed. All analogues have been modified in position 27 with Nle and with Gaba in position 30. Additional D-amino-acids have been inserted in the GHRH(1–30)-NH2 sequence A-1741: Nle27, Gaba30-GH-RH (1–30)-NH2 A-495: D-Ala2, Nle27, Gaba30-GH-RH (1–30 )-NH2 A-515: D Ala2, Leu15, Nle27, Gaba30-GH-RH (1–30)-NH2 A-527: D-Ala2, D-Arg11, Leu15, Nle27, Gaba30-GH-RH (1–30)-NH2. Our analogues were synthesized by solid phase peptide synthesis and were tested is two different in vitro systems and in rat pituitary cell cultures. A-495 and A-1741 were found to be the most active in releasing GH, however they showed different activities in the two different test systems. A-495 exhibited higher potency in the superfusion system (1.63 fold potency of the GHRH (1–29)-amide), while A-1741 evoked higher GH release from cultured pituitary cells (1.5–2.5 times higher than the GH-RH(1–44)-amide). The other analogues (A-515 and A-527) were found to be equipotent to the standard molecule. We can conclude that Nle27 and Gaba30 substitutions appeared to be a good modification in in vitro test systems, and Gaba30 substitution served as a good spacer during the synthesis, since it made the coupling of the C-terminal amino acids easier and produced quantitative coupling. In addition to the advantageous properties in the synthesis these modifications with or without D-Ala at the N-terminus increased the in vitro biological activity to 1.5–2.5 fold of the GHRH molecule. The additional substitution of Gly15 with Leu and Arg11 with D-Arg did not improve the in vitro GH-releasing activity of our analogues. A detailed in vivo investigation, which is essential for the future clinical use, hasbeen performed and written in Part II of this paper.
- GHRH analogues superfusion
- cell culture
ASJC Scopus subject areas
- Endocrinology, Diabetes and Metabolism