Thyroid hormone stimulates hepatic IGF-I mRNA expression in a bony fish, the tilapia Oreochromis mossambicus, in vitro and in vivo.
To gain more knowledge about the physiological regulation of hepatic insulin-like growth factor-I (IGF-I) production in bony fish, we examined the potential influence of thyroid hormone (T3, 3,5,3'-triiodothyronine) on the expression of IGF-I in the liver of the tilapia Oreochromis mossambicus, using in vitro and in vivo methods. The in vitro experiments were performed using a recently established primary hepatocyte cell culture and IGF-I expression was determined by means of semiquantitative RT-PCR. T3 (100 nM) significantly enhanced the synthesis rate of IGF-I mRNA in short (>8h) and long (>42h) time courses. The stimulating effect of T3 was detected already after 1h. After 4h, the IGF-I mRNA expression was more than 150% of the starting amount. In long time courses, after 6h the IGF-I mRNA value was about 170% of that in untreated cells and at the end of the experiment, it was still three times higher than in the control. In addition, the increase in IGF-I mRNA expression evoked by T3 (1 nM to 1 microM) was dose-dependent. In the in vivo approach, 10 individuals of tilapia received 4 daily intraperitoneal injections of T3 (6 microg/g body weight). IGF-I mRNA was assessed using dot blot technique with a tilapia specific IGF-I cRNA probe. The T3 treatment led to an increase of the IGF-I mRNA level up to 45% in the liver compared to the untreated animals. In conclusion, our results show that T3 directly stimulates the hepatic production of IGF-I in the tilapia in vitro and in vivo and indicate that in tilapia liver regulatory mechanisms seem to exist, as they are discussed for mammals.
Schmid
Annette C
AC
Division of Neuroendocrinology, Institute of Anatomy, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.
Lutz
Ilka
I
Kloas
Werner
W
Reinecke
Manfred
M
D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000378:metabolism*; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000235:genetics; D008099:Liver / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017210:Tilapia / Q000502:physiology*; D014284:Triiodothyronine / Q000502:physiology*
D012333:RNA, Messenger; D014284:Triiodothyronine; D007334:Insulin-Like Growth Factor I