Ghrelin stimulation by hypothalamic-pituitary-adrenal axis activation depends on increasing cortisol levels

Ghrelin plasma concentration increases in parallel to cortisol after a standardized psychological stress in humans, but the physiological basis of this interaction is unknown. We aimed to elucidate this question by studying the ghrelin response to pharmacological manipulation of the hypothalamic-pituitary-adrenal (HPA) axis. Six lean, healthy male volunteers were examined under four experimental conditions. Blood samples were collected every 30 min for two sequential periods of two hours. Initially, a baseline period was followed by intravenous injection of a synthetic analog of ACTH (250 mu g). Subsequently, a single dose of metyrapone was administered at midnight and in the following morning, blood samples were collected for 2 h, followed by an intravenous injection of hydrocortisone (100 mg) with continued sampling. We show that increased cortisol serum levels secondary to ACTH stimulation or hydrocortisone administration are positively associated with plasma ghrelin levels, whereas central stimulation of the HPA axis by blocking cortisol synthesis with metyrapone is associated with decreased plasma ghrelin levels. Collectively, this suggests that HPA-axis-mediated elevations in ghrelin plasma concentration require increased peripheral cortisol levels, independent of central elevation of ACTH and possibly CRH levels.