Insulin-like growth factors decrease catecholamine content in PC12 rat pheochromocytoma cells

Insulin-like growth factors (IGFs) stimulate proliferation and differentiation of PC12 rat pheochromocytoma cells and modulate catecholamine release in bovine adrenal medullary cells. Dexamethasone increases catecholamine synthesis in PC12 cells. We therefore studied the effects of IGFs and dexamethasone on catecholamine content in PC12 cells. Dopamine (DA) and norepinephrine (NE) content of PC12 cells were measured after incubation for 72 h with IGFs (100 ng/ml) and/or dexamethasone (500 nM). IGF-I (100 ng/ml) and IGF-II (100 ng/ml) decreased DA and NE content to approximately 35% and approximately 25% of control, respectively. [Leu27]IGF-II, which binds to the IGF-I receptor with markedly decreased affinity, did not reduce catecholamine levels, indicating that the effect is likely to be mediated by the IGF-I receptor. Dexamethasone (500 nM) increased levels of DA and NE to 173 +/- 20% and 331 +/- 48% of controls, respectively. Coincubation with IGFs did not significantly affect the stimulation of DA by dexamethasone, but abolished the rise in NE. Levels of tyrosine hydroxylase mRNA, protein and activity were increased following incubation with dexamethasone, but were unchanged by IGFs. These results indicate that IGFs decrease catecholamine content in PC12 cells via the IGF-I receptor. Complex regulation involving multiple synthetic and/or degradative steps is implicated in this process.