The hexapeptide KP-102 (D-ala-D-beta-Nal-ala-trp-D-phe-lys-NH(2)) stimulates growth hormone release in a cichlid fish (Ooreochromis mossambicus).
Abstract Studies in mammals have shown that synthetic Met-enkephalin derivatives, called growth hormone-releasing peptides (GHRPs), stimulate growth hormone (GH) release. The present study was conducted to determine whether the GHRP, KP-102, specifically stimulates GH release in a teleost. Tilapia (Oreochromis mossambicus) were given a single intraperitoneal injection of KP-102 (D-Ala-D-beta;-Nal-Ala-Trp-D-Phe-Lys-NH(2)) or bovine GHRH(1-29)-amide or vehicle and blood was sampled at 1, 6 and 12 h after injection. KP-102 was administered at two doses of 1 ng/g and 10 ng/g body weight, whereas GHRH (positive control) was administered at a single dose of 10 ng/g body weight. Plasma levels of tilapia GH and prolactins (tPRL(177) and tPRL(188)) were determined by radioimmunoassay. As expected, GHRH injection significantly (P<0.001) elevated plasma GH levels (ng/ml) in tilapia at 6 h post-injection. KP-102 also significantly elevated GH levels (at the low dose) at 6 (P<0.05) and 12 (P<0.01) hours post-injection. There were no significant effects on plasma PRL(s) levels, although mean levels of both PRLs were elevated at 6 h post-injection. These results show for the first time that GHRPs stimulate GH release in teleosts and suggest that the GHRP receptor and possibly a "Ghrelin-like" ligand are also present in lower vertebrates.
Shepherd
B S
BS
Biotechnology Center, University of Connecticut, Storrs, Connecticut 06269, USA. bsshep2@pop.uky.edu
Eckert
S M
SM
Parhar
I S
IS
Vijayan
M M
MM
Wakabayashi
I
I
Hirano
T
T
Grau
E G
EG
Chen
T T
TT
D000704:Analysis of Variance; D000818:Animals; D004305:Dose-Response Relationship, Drug; D013006:Growth Hormone / Q000097:blood*; D009842:Oligopeptides / Q000494:pharmacology*; D011388:Prolactin / Q000097:blood; D011986:Receptors, Somatotropin / Q000378:metabolism; D017337:Sermorelin / Q000494:pharmacology; D013268:Stimulation, Chemical; D017210:Tilapia / Q000502:physiology*; D013997:Time Factors
D009842:Oligopeptides; D011986:Receptors, Somatotropin; D017337:Sermorelin; D011388:Prolactin; D013006:Growth Hormone; C091874:growth hormone-releasing peptide-2