Gabillard Jean-Charles, Weil Claudine, Rescan Pierre-Yves, Navarro Isabel, Gutiérrez Joaquim, Le Bail Pierre-Yves
Equipe Croissance et Qualité de la Chair des Poissons, Station Commune de Recherches en Ichtyophysiologie, Biodiversité et Environnement SCRIBE-INRA, Campus Beaulieu, 35042 Rennes, France.
Gen Comp Endocrinol. 2003 Sep;133(2):233-42. doi: 10.1016/s0016-6480(03)00167-9.
Recently, we have demonstrated in rainbow trout that environmental temperature may, independently of nutritional status, directly stimulate plasma growth hormone (GH) that is recognised as being an insulin-like growth factor (IGF) system regulator. The aim of this study was to determine whether temperature may directly regulate the IGF system or indirectly regulate it through plasma GH or nutritional status. For this purpose, rainbow trout were reared at 8, 12, or 16 degrees C and fed either ad libitum (similar nutritional status) to evidence the global effect of temperature, or with the same ration (1.2% body weight/day), to determine the temperature effect in fish with the same growth rate. Endocrine and autocrine/paracrine regulations of the IGF system were determined by measuring plasma IGF1 and IGF2, liver and muscle IGF1 and IGF2 mRNA as well as IGFRIa, IGFRIb mRNA, and the quantity of IGF type I receptor in muscle. Our results show that neither rearing temperature nor the nutritional status of fish affected the expression of both IGF receptor genes in muscle. Nevertheless, the quantity of IGF type I receptor determined by a binding study, appeared to be inversely proportional (P<0.05) to the rearing temperature without any relationship with nutritional status, suggesting a direct effect of temperature on its turnover. After 2 weeks of treatment, the levels of IGF1 mRNA in muscle at 8 degrees C were 2-fold higher (P<0.05) than at 16 degrees C in both ad libitum and restricted feed fish, whereas after 6 weeks, this difference was no longer observed. In both experiments, the levels of plasma IGF2 were 10-fold higher than the levels of plasma IGF1 (mean 105+/-3.0 versus 13.5+/-0.6 ng/ml), and plasma levels were correlated with their respective mRNA liver concentrations (r2=0.14 and 0.25, respectively; P<0.01). In the ad libitum feeding experiment, plasma and mRNA levels of IGF1 were related to the rearing temperature (P<0.05), while for IGF2 no effect was seen. In contrast, in the restricted feeding experiment, plasma and IGF2 mRNA levels were inversely proportional to the rearing temperature (P<0.0001) while plasma IGF1 was unaltered. Levels of plasma IGF1 were related to the growth rate in both experiments, while levels of plasma IGF2 appeared to be associated with the nutritional status of the fish. Our results suggest that the autocrine/paracrine expression of IGF1 and IGF2 in muscle is not a key regulator of the growth promoting effect of temperature. Conversely, temperature seems to promote growth through IGF1 secretion by the liver following GH stimulation, and impairment of nutritional status would prevent the IGF1 stimulation by temperature. In addition, the growth-promoting effect of temperature did not affect plasma IGF2, which appeared to be more related to the metabolic status of the fish.
最近，我们在虹鳟鱼身上证实，环境温度可能独立于营养状况，直接刺激血浆生长激素（GH），而生长激素被认为是胰岛素样生长因子（IGF）系统的调节剂。本研究的目的是确定温度是直接调节IGF系统，还是通过血浆GH或营养状况间接调节。为此，将虹鳟鱼饲养在8℃、12℃或16℃，随意投喂（营养状况相似）以证明温度的总体影响，或投喂相同的饲料量（体重的1.2%/天），以确定相同生长速率的鱼的温度影响。通过测量血浆IGF1和IGF2、肝脏和肌肉中的IGF1和IGF2 mRNA以及IGFRIa、IGFRIb mRNA和肌肉中I型IGF受体的数量，确定IGF系统的内分泌和自分泌/旁分泌调节。我们的结果表明，饲养温度和鱼的营养状况均不影响肌肉中两种IGF受体基因的表达。然而，结合研究确定的I型IGF受体数量似乎与饲养温度呈反比（P<0.05），与营养状况无关，这表明温度对其周转有直接影响。处理2周后，8℃时肌肉中IGF1 mRNA水平在随意投喂和限饲的鱼中均比16℃时高2倍（P<0.05），而6周后，这种差异不再明显。在两个实验中，血浆IGF2水平均比血浆IGF1水平高10倍（平均105±3.0对13.5±0.6 ng/ml），且血浆水平与其各自在肝脏中的mRNA浓度相关（r2分别为0.14和0.25；P<0.01）。在随意投喂实验中，IGF1的血浆和mRNA水平与饲养温度有关（P<0.05），而对IGF2则无影响。相反，在限饲实验中，血浆和IGF2 mRNA水平与饲养温度呈反比（P<0.0001），而血浆IGF1未改变。在两个实验中，血浆IGF1水平均与生长速率有关，而血浆IGF2水平似乎与鱼的营养状况有关。我们的结果表明，肌肉中IGF1和IGF2的自分泌/旁分泌表达不是温度促进生长作用的关键调节因子。相反，温度似乎通过GH刺激后肝脏分泌IGF1来促进生长，而营养状况受损会阻止温度对IGF1的刺激。此外，温度的促生长作用不影响血浆IGF2，血浆IGF2似乎与鱼的代谢状况更相关。
