Circulating human corticotropin-releasing factor-binding protein levels following cortisol infusions

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.