Effects of insulin-like growth factors (IGF-I and -II) on growth hormone and prolactin release and gene expression in euryhaline tilapia, Oreochromis mossambicus

We investigated in vitro effects of insulin-like growth factors (IGF-I and -II) on growth hormone (GH) and prolactin (PRL) release and gene expression in euryhaline tilapia, Oreochromis mossambicus. Pituitaries were removed from freshwater-acclimated adult males and incubated for 2-24h in the presence of human IGF-I or -II at doses ranging from 1-1000ng/ml (0.13-130nM). IGF-I at concentrations higher than 10ng/ml and IGF-II higher than 100ng/ml significantly inhibited GH release after 8, 16, and 24h. No effect of IGFs was seen during the first 4h of incubation. 1GFs at the same concentrations also significantly attenuated GH gene expression after 24h, although no effect was seen at 2h. By contrast, PRL188 release was stimulated significantly and in a dose-related manner by IGF-I at concentrations higher than 10ng/ml and by IGF-II at concentrations higher than 100ng/ml within 2h. No stimulation was observed after 4h. Similarly, both IGFs at concentrations higher than 10ng/ml increased PRL177 release within 2h. However, no significant effect of IGF-I or -II was observed on mRNA levels of both PRLs after 2 and 24h at all concentrations examined. These results clearly indicate differential regulation of GH and PRL release and synthesis by 1GFs in the tilapia pituitary, i.e., rapid-acting, stimulatory effects of IGFs on PRL release and slow-acting, inhibitory effects on GH release and synthesis. (C) 2002 Elsevier Science (USA). All rights reserved.