Shimizu Shunsuke, Kaiya Hiroyuki, Matsuda Kouhei
Laboratory of Regulatory Biology, Graduate School of Science and Engineering, University of Toyama, 3190-Gofuku, Toyama, Toyama 930-8555, Japan.
Department of Biochemistry, National Cerebral and Cardiovascular Center (NCVC) Research Institute, Suita, Osaka 565-8565, Japan.
Peptides. 2014 Jan;51:74-9. doi: 10.1016/j.peptides.2013.10.028. Epub 2013 Nov 7.
Ghrelin is a potent orexigenic peptide implicated in appetite regulation in rodents. However, except for teleost fish, the involvement of ghrelin in the regulation of feeding in non-mammalian vertebrates has not been well studied. Anuran amphibian larvae feed and grow during the pre- and prometamorphic stages, but, thereafter they stop feeding as the metamorphic climax approaches. Therefore, orexigenic factors seem to play important roles in growing larvae. In the present study, we examined the effect of intraperitoneal (IP) or intracerebroventricular (ICV) administration of synthetic bullfrog ghrelin (n-octanoylated 28-amino acid form) on food intake in larvae at the prometamorphic stages. Cumulative food intake was significantly increased by IP (8 and 16pmol/g body weight (BW)) or ICV (0.5 and 1pmol/g BW) administration of ghrelin during a 15-min observation period. The orexigenic action of ghrelin at 8pmol/g BW (IP) or at 0.5pmol/g BW (ICV) was blocked by treatment with a growth hormone secretagogue-receptor antagonist, [D-Lys(3)]GHRP-6 at 80pmol/g BW (IP) or at 5pmol/g BW (ICV). We then investigated the effect of feeding status on expression levels of the ghrelin transcript in the hypothalamus and gastrointestinal tract. Ghrelin mRNA levels in both were decreased 15 and 60min after feeding. These results indicate that ghrelin acts as an orexigenic factor in bullfrog larvae.
胃饥饿素是一种强效的促食欲肽，参与啮齿动物的食欲调节。然而，除硬骨鱼外，胃饥饿素在非哺乳类脊椎动物摄食调节中的作用尚未得到充分研究。无尾两栖类幼虫在前变态期和前变态高峰期摄食并生长，但此后随着变态高潮的临近，它们停止摄食。因此，促食欲因子似乎在生长中的幼虫中发挥重要作用。在本研究中，我们检测了腹腔注射（IP）或脑室内注射（ICV）合成牛蛙胃饥饿素（正辛酰化的28个氨基酸形式）对前变态期幼虫食物摄入量的影响。在15分钟的观察期内，腹腔注射（8和16 pmol/g体重（BW））或脑室内注射（0.5和1 pmol/g BW）胃饥饿素可显著增加累积食物摄入量。胃饥饿素在8 pmol/g BW（腹腔注射）或0.5 pmol/g BW（脑室内注射）时的促食欲作用被生长激素促分泌素受体拮抗剂[D-Lys(3)]GHRP-6以80 pmol/g BW（腹腔注射）或5 pmol/g BW（脑室内注射）处理所阻断。然后，我们研究了摄食状态对下丘脑和胃肠道中胃饥饿素转录本表达水平的影响。摄食后15分钟和60分钟，下丘脑和胃肠道中的胃饥饿素mRNA水平均下降。这些结果表明，胃饥饿素在牛蛙幼虫中作为一种促食欲因子发挥作用。
