Fox Bradley K, Riley Larry G, Dorough Casey, Kaiya Hiroyuki, Hirano Tetsuya, Grau E Gordon
Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, USA.
Zoolog Sci. 2007 Apr;24(4):391-400. doi: 10.2108/zsj.24.391.
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.
胃饥饿素是一种主要在胃的泌酸黏膜细胞中合成的脑肠肽，具有强大的生长激素（GH）释放和促食欲活性。最近，在莫桑比克罗非鱼（Oreochromis mossambicus）中鉴定出了两种形式的胃饥饿素，即胃饥饿素 -C8和 -C10。本研究描述了这些内源性胃饥饿素对GH/胰岛素样生长因子 -I（IGF-I）轴的体外和体内作用。孵育4小时和8小时后，胃饥饿素 -C8（100 nM）刺激垂体细胞原代培养物中GH的释放，而对催乳素（PRL）的释放没有影响。在孵育6小时期间，胃饥饿素 -C8和 -C10（100 nM）对GH释放的刺激作用被与生长激素促分泌素受体拮抗剂[D-Lys(3)]-GHRP-6（10 microM）预孵育所阻断。腹腔注射胃饥饿素 -C8（1 ng/g体重）和 -C10（0.1和1 ng/g体重）5小时后显著提高了血浆GH水平。注射两种形式的胃饥饿素（0.1和1 ng/g体重）后，肝脏中IGF-I和GH受体（GHR）mRNA的表达也显著增加，尽管对血浆IGF-I水平没有影响。在接下来的实验中，两种形式的胃饥饿素（1 ng/g体重）在注射后10小时显著提高了血浆IGF-I水平。两种胃饥饿素对血浆PRL水平均未观察到显著影响。在垂体中发现了两种形式的生长激素促分泌素受体（GHSR-1a和 -1b），这清楚地表明罗非鱼胃饥饿素主要通过生长激素促分泌素受体刺激GH释放。对肝脏中IGF-I和GHR表达的刺激表明胃饥饿素在罗非鱼中具有代谢作用。
