Leptin directly stimulates parathyroid hormone secretion

Leptin is best known for its modulatory effects on food intake [1] but also participates in the regulation of calciotropic hormones. Leptin has been reported to stimulate bone secretion of fibroblast growth factor 23 (FGF23) [2], a major phosphaturic hormone, and to decrease 1,25(OH)2-vitamin D3 both directly, by decreasing 1-alpha-hydroxylase activity in the kidney, and indirectly, through increasing levels of FGF23 [2, 3]. Although several studies point toward a relationship between plasma leptin levels and parathyroid hormone (PTH) secretion [4–6], the connection has not been fully elucidated. Plasma PTH concentrations tend to be elevated in obesity, and it has been suggested that the increased PTH levels found in obese persons may be secondary to hyperleptinemia [5]. However, it is not clear whether there is a direct relationship between leptin and PTH or whether the relationship is indirect and mediated by decreased 1,25(OH)2-vitamin D3 [5, 7]. The aim of this study was to test the hypothesis that leptin directly stimulates PTH secretion by the parathyroid glands.