Abstract
Leptin and thyroid hormones (TH) have the ability to increase energy expenditure. Biological effects of TH are dependent on thyroxine (T4) to triiodothyronine (T3) conversion by deiodinase type 1 (D1) and type 2 (D2). Leptin has been shown to stimulate the hypothalamus-pituitary-thyroid axis and, also, to modulate 5′-deiodinases in different tissues, depending on energetic status of animals. Here, we examined the acute effects of leptin on hypothalamic, pituitary and BAT D2 and pituitary D1 activities. Male fed rats received a single subcutaneous injection of saline or leptin (8 μg/100 g BW) and sacrificed 2 hours later. Leptin promoted an important decrease in hypothalamic D2 (55% reduction, p <0.001) with no changes in pituitary D2, in concomitance with a 2-fold rise in serum TSH, suggesting that leptin acted at hypothalamus in order to stimulate TRH-TSH axis. In addition, BAT D2 was decreased by 25% (p<0.05). In contrast, pituitary D1 showed a 2-fold increase (p<0.001), indicating that, as demonstrated before for liver and thyroid D1, the pituitary enzyme is also acutely up-regulated by leptin. Serum concentrations of insulin and TH of leptin-injected animals remained unchanged. Regulation of 5′-deiodinases directing the local T3 production, is a mechanism by which leptin may alter hypothalamic, pituitary and BAT functions.
Key words
Thyrotropin - thyroid hormones - insulin - thyrotropin-releasing hormone
References
in vivo TSH secretion by leptin.
Regul Pept.
2000;
92
25-29
in vivo and in vitro studies.
J Endocrinol.
2002;
174
121-125
3 production is mediated by brown adipose tissue type 2 deiodinase.
Am J Physiol Endocrinol Metab.
2002;
283
E980-E987
Marmota flaviventris ).
J Comp Physiol.
2004;
174
633-639
in vivo effects of leptin and leptin fragments on corticosteroid hormone secretion and entero-insular axis in the rat.
Int J Mol Med.
2004;
13
829-834
Correspondence
cpazosm@biof.ufrj.br
