Mechanisms of norepinephrine mediated corticotropin-releasing factor-41 release from cultured fetal hypothalamic...

Catecholamines have been shown to activate hypothalamic corticotropin-releasing factor-41 (CRF) synthesis and release. In order to study the mechanisms involved, fetal hypothalamic cells were cultured and CRF release was measured by radioimmunoassay. Norepinephrine (NE) induced CRF release in a dose-dependent manner. Further studies were performed with a protein kinase C inhibitor, H-7(1-(5-isoquinolinesulfonyl)-2-methylpiperazine) and a protein kinase A inhibitor, IP-20. NE-stimulated CRF release was reduced by H-7 (5 and 50 microM) in a dose-dependent fashion, while 5 microM IP-20 resulted in a small but significant inhibition. Pretreatment of the cells for 15 h with 20 and 200 nM 12-O-tetradecanoylphorbol-13-acetate, which down-regulates protein kinase C activity, blocked the release of CRF in response to NE (1 microM), further supporting protein kinase C as a mediator for NE-activated CRF release. Pretreatment with 50 and 500 ng/ml pertussis toxin (15 h) resulted in a dose-dependent inhibition of NE-activated CRF release. Both dexamethasone and aldosterone at the concentrations of 1 microM reduced NE-induced CRF release. These results suggest that CRF can be released from hypothalamic neurons in response to NE through both protein kinase C- and protein kinase A-dependent mechanisms, and that pertussis toxin-sensitive G-proteins are also involved in this response. Furthermore, glucocorticoids and mineralocorticoids can reduce NE-activated CRF release from cultured hypothalamic cells.