Cortisol response to individualised graded insulin infusions: a reproducible biomarker for CNS compounds inhibiting HPA activation.

AIM: To determine the potential of cortisol secretion, in response to a physiological stressor, as a biomarker for centrally active compounds targeting the hypothalamic-pituitary-adrenocortical (HPA) axis. METHODS: Cortisol response to hypoglycaemia was measured in 26 healthy males in two stages: firstly to derive an algorithm for individualized, graded insulin infusion rates to achieve defined hypoglycaemic targets over 3 h and secondly to determine the inter- and intra-subject variability of cortisol response to hypoglycaemia over two identical periods by measuring the maximum (t(max) ), time to maximum (C(max) ) response and cortisol area under the response curve (AUC). RESULTS: Hypoglycaemia induced a consistent cortisol response starting at approximately 1 h, corresponding to blood glucose concentrations of approximately 3.3 mmol l⁻¹, and peaking approximately 3 h after the start of infusion. The inter- and intra-subject coefficients of variation (CVs) of cortisol response were approximately 19 and 19% (AUC), 15 and 19 % (C(max) ) and 10 and 14% (t(max) ), respectively. The intra-subject CVs for the ratio of maximum cortisol response to baseline concentration and rate of initial cortisol response between study days were more variable (32.8% and 59.0%, respectively). The blood glucose-cortisol response model derived from the study was predictive of the individual observed cortisol responses, and estimated a blood glucose EC(50) associated with onset of the cortisol response of 3.3 mmol l⁻¹. CONCLUSIONS: Gradual hypoglycaemia is an effective, reproducible and well-tolerated method of stimulating a cortisol response and may therefore be useful in assessing the neuroendocrine response to HPA axis inhibitors, such as corticotropin-releasing hormone-1 (CRH-1) antagonists.