Ghrelin and thyroid function

Ghrelin is a 28 amino acid hormone identified as the endogenous ligand for the Growth Hormone Secretagogue Receptor (GHS-R). This hormone is mainly produced by cells in the gastric fundus, but it is also produced in other organs, including the thyroid. Thyroid function can influence the serum concentrations of ghrelin. Several studies revealed that the serum levels of ghrelin are reduced in hyperthyroidism, being normalized by medical treatment with anti-thyroid drugs, while conflicting data have been reported in hypothyroid patients. In order to explain the changes in the serum concentrations of ghrelin in thyroid dysfunctions, several hypotheses were proposed: (i) the higher or lower serum concentrations of ghrelin could be a secondary phenomenon, resulting from changes in insulin levels during hyperthyroid or hypothyroid state; (ii) the thyroid status by itself could be responsible for the modulation of serum ghrelin; (iii) the changes in serum ghrelin concentrations could represent a compensatory effect to the alterations of the GH - IGF-I axis induced by an excess or a deficiency of thyroid hormones. Ghrelin may play a role in the proliferation of thyrocytes or in the development of thyroid tumour, however the clinical relevance and the mechanism underlying these effects of ghrelin are poorly understood.