Differential effect of insulin-like growth factor I on in vitro gonadotropin subunits expression in Atlantic salmon

In the present study a serum-free primary culture of pituitary cells was used to study the direct effect of insulin-like growth factors (IGFs) on gonadotropin gene expression in immature Atlantic salmon. Treatment with IGF I increased the expression of the luteinizing hormone (LH) beta subunit in a dose-dependent manner. IGF I and IGF II had similar potencies, but insulin was less effective in stimulating LH-beta subunit expression. On the other hand, IGFs or insulin had no effect on the expression of the follicle-stimulating hormone (FSH) beta-subunit. The results indicate that the stimulatory effect of IGF I on LH synthesis is exerted through a specific increase of the transcription level of the LH beta subunit.