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Studies involving regulation of corticotropin-releasing hormone (CRH) in vitro have been used to validate findings obtained in vivo and more importantly have been used as model systems to better understand signalling mechanisms responsible for the expression of the CRH gene and peptide. Many in vitro studies examining CRH have utilized hypothalamic tissue while a few have focused on the amygdala. Clonal cell lines have also been utilized as models of central nervous system CRH neurons. Stimuli that have been implicated in regulating hypothalamic CRH regulation in vitro include protein kinase A (PKA) and protein kinase C (PKC) activators, glucocorticoids, biogenic amines, cytokines and the gaseous neurotransmitters. Amygdalar CRH levels in vitro are affected by some of the same stimuli that regulate hypothalamic CRH; however there is evidence supporting differential regulation of CRH in these two brain regions by some of the same stimuli. Only a few studies in aggregate have investigated signal transduction mechanisms and these studies have focused on PKA- and glucocorticoid-mediated changes in CRH expression. Thus, much more investigative work in better understanding CRH regulation in vitro is needed.

Corticotropin-releasing factor-binding protein (CRF-BP) is a 37 kDa protein present in the brain and plasma and is known to regulate the actions of CRF. It has been demonstrated that CRF-BP in the brain and the pituitary appears to be positively regulated by glucocorticoids. In this study, the effect of various doses of hydrocortisone infusions on plasma CRF-BP levels was assessed. Four groups of 10 age-matched males received a 100 min infusion of either placebo (saline), 40 microg/kg/h, 300 microg/kg/h or 600 microg/kg/h hydrocortisone. CRF-BP levels were measured via a LIRMA. In addition, levels of plasma ACTH and cortisol were measured by standard radioimmunoassay. As expected, plasma cortisol levels increased and plasma ACTH levels were suppressed following the infusion. When expressed as proportion of pre-infusion baseine, no significant changes in plasma CRF-BP levels were observed following the infusion for all hydrocortisone groups relative to the control group. However, a significant time-averaged positive correlation was found between CRF-BP and cortisol levels at low to moderate, but not high, cortisol levels. The data obtained in this study indicate that CRF binding protein levels within the time course examined may slightly appear to be affected in the peripheral circulation in response to pronounced, sustained hypercortisolemia.

Preliminary data suggest that amygdalar corticotropin-releasing factor (CRF) is regulated by nicotinic agonists. We sought to confirm and extend these observations by determining the effects of various concentrations of nicotine on CRF messenger RNA expression in the AR-5 immortalized amygdalar cell line. Nicotine produced concentration- and time-dependent increases in CRF mRNA. This cell line thus confirms that nicotinic agonists stimulate amygdalar CRF and appears to be a useful model for studying molecular factors important in this interaction.