Hyperthyroidism is associated with suppressed circulating ghrelin levels.

Ghrelin stimulates GH secretion as well as appetite and food intake. To explore whether ghrelin is involved in the regulation of appetite and body weight in hyperthyroidism, circulating ghrelin levels were measured in nine hyperthyroid patients before and after medical treatment and compared with those in eight healthy control subjects. All participants were studied in the postabsorptive state and during a 3-h euglycemic hyperinsulinemic clamp. Before treatment the patients had 3- to 5-fold elevations of T(3), and during treatment the patients gained 5 kg of body weight. Ghrelin levels were decreased in hyperthyroidism both in the fasting state (hyperthyroid, 1080 +/- 195 pg/ml; euthyroid, 1480 +/- 215 pg/ml; P = 0.03) and during clamp (hyperthyroid, 833 +/- 150 pg/ml; euthyroid, 1210 +/- 180 pg/m; P = 0.02). After treatment, ghrelin levels did not differ from those in control subjects. In all three study groups the clamp significantly reduced ghrelin levels compared with fasting levels. In conclusion, ghrelin levels are reduced in hyperthyroidism and become normalized by medical antithyroid treatment. Hyperinsulinemia suppresses ghrelin regardless of thyroid status. Ghrelin is not a primary stimulator of appetite and food intake in hyperthyroidism, and the mechanisms underlying the suppressive effect of hyperthyroidism on ghrelin secretion remain unclear.