Effects of peripheral administration of GH and IGF-I on gene expression in the hippocampus of hypophysectomised rats.

Growth hormone (GH) increases insulin-like growth factor I (IGF-I) production and both hormones affect hippocampal plasticity. We have previously shown that Hbb and Alas2 in the rat hippocampus were robustly regulated by GH-infusions for six days, whereas other transcripts were weakly affected. Here, we explored the effects of prolonged GH administration on transcripts linked to neuroprotection and investigated whether serum IGF-I administration may exert similar effects. Hypophysectomised female rats were infused with GH or IGF-I for 19 days. Hbb, Alas2 and seven additional GH- and IGF-I-related transcripts were quantified by Q-RT-PCR in rat hippocampus. Three transcripts, Hbb, Alas2, and Alox15 were increased by both GH and IGF-I administration. The other transcripts were marginally affected. The 19-day GH-infusion induced similar effects as those reported after 6-day GH treatment, with the addition of the regulation of transcript Alox15. IGF-I induced altered gene expression in relation to its effect on weight gain. This study underlines that there is an entity of transcripts involved in neuroprotection and vascular tone that is regulated by both systemic GH and IGF-I. For other transcripts, the longer duration of this study did not significantly enhance the marginal effects of GH administration seen previously.