The Thyroid Hormone Axis

The effects of central orexins on TSH secretion have not been investigated in detail. Mitsuma et al. (26) administered orexin-A (50 pg kg iv) and observed a dose-dependent decrease in plasma TSH. They also observed a reduction in hypothalamic TRH secretion in response to orexin-A and suggested a hypothalamic mechanism for the action of systemic orexin-A since no pituitary effect was observed. No significant changes in TRH secretion were observed when orexin-A was administered to hypothalamic...