Ghrelin and GHRP-6-induced ACTH and cortisol release in thyrotoxicosis

Thyrotoxicosis might alter the hypothalamic-pituitary-adrenal (HPA) axis. We evaluated the effects of ghrelin and GHRP-6 on the HPA axis in 20 hyperthyroid patients and in 9 controls. Mean basal cortisol (μg/dl) and ACTH (pg/ml) levels were higher in hyperthyroidism (cortisol: 10.7 ± 0.7; ACTH: 21.5 ± 2.9) compared to controls (cortisol: 8.1 ± 0.7; ACTH: 13.5 ± 1.8). In thyrotoxicosis ∆ AUC cortisol values (μg/dl.90 min) after ghrelin (484 ± 80) and GHRP-6 (115 ± 63) were similar to controls (ghrelin: 524 ± 107; GHRP-6: 192 ± 73). A significant increase in ∆ AUC ACTH (pg/ml.90 min) after ghrelin was observed in thyrotoxicosis (4,189 ± 1,202) compared to controls (1,499 ± 338). ∆ AUC ACTH values after GHRP-6 were also higher, although not significantly (patients: 927 ± 330; controls: 539 ± 237). In summary, our results suggest that ghrelin-mediated pathways of ACTH release might be activated by thyroid hormone excess, but adrenocortical reserve is maintained.