Hyperthyroidism Is Associated with Suppressed Circulating Ghrelin Levels

Abstract

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.

Circulating ghrelin in thyroid dysfunction is related to insulin resistance and not to hunger, food intake or anthropometric changes

“…However, if this were the case, the opposite would be expected in hypothyroidism where ghrelin levels were similar to healthy controls before and after treatment. Furthermore, glucose and insulin concentrations and insulin sensitivity were normal in hypothyroidism, as previously described (23). This observation could contribute to explain why ghrelin levels were not altered in hypothyroidism.…”

“…In the present study, ghrelin levels increased in hyperthyroidism after treatment, in spite of an increase in BMI, waist-to-hip ratio and percentage of body fat and, in hypothyroidism, BMI decreased without modification of ghrelin levels suggesting an absence of relationship between ghrelin and these anthropometric changes in thyroid dysfunction. Additionally, we did not find any correlation between ghrelin and thyroid hormone levels as previously described (23).…”

“…To date, only one study has been performed in a small number of patients with hyperthyroidism, which reported suppressed circulating ghrelin levels despite being in a negative energy balance state (23). In this study food intake was not evaluated.…”

Ghrelin in obesity and endocrine diseases

“…It appears that the hyperphagia of hyperthyroidism is not mediated by circulating ghrelin (Katergari et al, 2008). Circulating plasma ghrelin levels are reduced in hyperthyroidism as compared to the euthyroid state (Altinova et al, 2006a), exhibit a positive correlation with thyroid stimulating hormone (TSH) levels (Sawicka et al, 2010) and rise to normal levels with pharmacological therapy of hyperthyroidism (Braclik et al, 2008;GimenezPalop et al, 2005;Riis et al, 2003;Rojdmark et al, 2005;Theodoropoulou et al, 2009).…”

“…Insulin resistance is increased in hyperthyroidism (Gimenez-Palop et al, 2005) and hyperinsulinaemia has been shown to suppress ghrelin levels (Saad et al, 2002) regardless of thyroid status (Riis et al, 2003).…”