Estradiol-17beta and dihydrotestosterone differentially regulate vitellogenin and insulin-like growth factor-I production in primary hepatocytes of the tilapia Oreochromis mossambicus.

Effects of estradiol-17beta (E2) and 5alpha-dihydrotestosterone (DHT) on the production of vitellogenin (Vg), insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGFBPs) were examined in vitro using primary hepatocyte culture of the tilapia. Estradiol produced a significant and concentration-related stimulation of Vg release and concomitant, concentration-related reduction in IGF-I mRNA expression in both male and female hepatocytes. In male hepatocytes, DHT significantly increased IGF-I expression, whereas DHT inhibited IGF-I expression and stimulated Vg release in female hepatocytes. Estradiol treatment significantly reduced the release of 25 kDa IGFBP, while stimulating the release of 30 kDa IGFBP from male hepatocytes. In female hepatocytes, E2 significantly increased both 25 and 30 kDa IGFBPs. In male hepatocytes, DHT significantly reduced 25 kDa IGFBP without affecting 30 kDa IGFBP. Conversely, DHT treatment of hepatocytes from female fish significantly increased both the 25 and 30 kDa IGFBPs. The different growth rates observed between male and female tilapia may be a result of gonadal steroid hormones eliciting direct and antagonistic effects on production of IGF-I (growth) and Vg (reproduction) in the liver. Indeed, the different growth patterns likely result from a difference in the sensitivity of male and female hepatocytes to gonadal steroid hormones. These results also indicate direct effects of gonadal steroid hormones on production of IGFBPs, which may play a role in regulating IGF-I mediated growth.