Effects of homologous ghrelins on the growth hormone/insulin-like growth factor-I axis in the tilapia, Oreochromis mossambicus.
Ghrelin is a gut-brain peptide synthesized mainly in the oxyntic mucosal cells of the stomach, and has potent growth hormone (GH)-releasing and orexigenic activities. Recently, two forms of ghrelin, ghrelin-C8 and -C10, were identified in the Mozambique tilapia (Oreochromis mossambicus). The present study describes in vitro and in vivo effects of these endogenous ghrelins on the GH/insulin-like growth factor-I (IGF-I) axis. Ghrelin-C8 (100 nM) stimulated GH release from primary cultures of pituitary cells after 4 and 8 h of incubation, whereas no effect was seen on prolactin (PRL) release. Stimulatory effects of ghrelin-C8 and -C10 (100 nM) on GH release during 6 h of incubation were blocked by pre-incubation with GHS receptor antagonist, [D-Lys(3)]-GHRP-6 (10 microM). Intraperitoneal injection of ghrelin-C8 (1 ng/g body weight) and -C10 (0.1 and 1 ng/g body weight) significantly increased plasma GH levels after 5 h. Significant increases were observed also in hepatic expression of IGF-I and GH receptor (GHR) mRNA following injections of both forms of ghrelin (0.1 and 1 ng/g body weight), although there was no effect on plasma levels of IGF-I. In the next experiment, both forms of ghrelin (1 ng/g body weight) significantly increased plasma IGF-I levels 10 h after the injection. No significant effect of either ghrelin was observed on plasma PRL levels. Both forms of GHS receptor (GHSR-1a and -1b) were found in the pituitary, clearly indicating that tilapia ghrelins stimulate primarily GH release through the GHS receptor. Stimulation of hepatic expression of IGF-I and GHR suggests metabolic roles of ghrelin in tilapia.
Fox
Bradley K
BK
Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, USA.
Riley
Larry G
LG
Dorough
Casey
C
Kaiya
Hiroyuki
H
Hirano
Tetsuya
T
Grau
E Gordon
EG
D000818:Animals; D004305:Dose-Response Relationship, Drug; D054439:Ghrelin; D013006:Growth Hormone / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008099:Liver / Q000378:metabolism; D008297:Male; D036361:Peptide Hormones / Q000494:pharmacology*; D010902:Pituitary Gland / Q000187:drug effects / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D011863:Radioimmunoassay; D011986:Receptors, Somatotropin / Q000037:antagonists & inhibitors / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D052683:Somatotrophs / Q000187:drug effects / Q000378:metabolism; D017210:Tilapia / Q000378:metabolism; D013997:Time Factors
D054439:Ghrelin; D036361:Peptide Hormones; D012333:RNA, Messenger; D011986:Receptors, Somatotropin; D007334:Insulin-Like Growth Factor I; D011388:Prolactin; D013006:Growth Hormone