Absence of thyrotropin-induced increase in leptin levels in patients with history of differentiated thyroid carcinoma undergoing recombinant human thyrotropin testing

Background: Some extra-thyroid effects of TSH have been described in vitro and in vivo. TSH has recently been suggested to induce interleukin-6 secretion by adipocytes. Leptin is the main protein secreted by adipose tissue. Objective: The aim of our study was to evaluate the acute effect of the recombinant human TSH (rhTSH)-induced TSH surge on serum leptin levels in thyroidectomized patients undergoing levothyroxine (L-T4) suppressive therapy for differentiated thyroid carcinoma (DTC). Design: A cohort of 15 female DTC patients was evaluated. Standard rhTSH testing was performed. Leptin, TSH, thyroid hormones, and thyroglobulin were measured before and 3, 6, and 9 days after rhTSH testing. Some metabolic parameters were also evaluated at the baseline. Results: Baseline leptin levels were 12.2±3.2 μg/l. Only body mass index (BMI) correlated significantly (p<0.05) with leptin levels. After rhTSH administration, TSH levels increased significantly (p<0.001), while thyroid hormones remained unchanged. Twenty hours after the last rhTSH administration, leptin (11.8±3.0 μg/l) levels were unchanged. The maximal TSH level was negatively related with BMI (p<0.05), but no correlation between maximal TSH and leptin levels after rhTSH was noted. Conclusions: Our in vivo experimental model suggests that an acute TSH increase after rhTSH testing is ineffective in changing circulating leptin levels.