The Effects of Administration of Exogenous Thyrotropin-Releasing Hormone (TRH) to Levels of Insulin, C-peptide and Glucagon in Euthyroid and Hyperthyroid Subjects

Abstract

Hyperthyroidism is associated with alterations in insulin, C-peptide and glucagon levels. Thereby exogenous TRH effects the secretion of these hormones. We aimed to assess the effect of exogenous TRH administration to the secretion of insulin, C-peptide, glucagon and plasma glucose in euthyroid and hyperthyroid patients. Five untreated hyperthyroid and 13 euthyroid patients took part in the study. Blood samples for measurements of TSH, insulin, C-peptide, glucagon and glucose were obtained before, and 20 and 40 min after IV administration of 400 mcg TRH in both groups. Basal insulin levels were higher in hyperthyroid subjects than in euthyroids while there was not any difference in C-peptide and glucagon between two groups. TRH stimulation caused in increased insulin, C-peptide and glucagon levels in euthyroid subjects. In the hyperthyroid group there was a non-significant increase in insulin, thereby a rise in C-peptide at the 40th min while glucagon levels showed a decline at both the 20th and 40th min following TRH stimulation. Hyperthyroidism under basal circumstances is associated with hyperinsulinism. Exogenous TRH administration increased insulin, C-peptide and glucagon levels in euthyroid subjects. Insulin levels did not alter, plasma glucose and c-peptide increased and glucagon levels decreased following TRH administration in hyperthyroid subjects.