Leptin and leptin receptor expression in rat and mouse pituitary cells

Leptin is a circulating hormone secreted mainly by adipose tissue. Recent s tudies have shown leptin production by other tissues, including the placent a, stomach, and mammary tissues. Various reports have suggested that the an terior pituitary may have a role in the regulatory effects of leptin. We re cently localized leptin in the human anterior pituitary, but analysis of le ptin in rodent pituitary has not been previously reported. In this study we examined rat and mouse pituitary tissues and Various cell lines for leptin by RT-PCR, immunohistochemistry, and Western blotting. Leptin receptor mes senger RNA was also examined in these tissues by RT-PCR. Leptin was present in a small percentage of rat (4.8 +/- 0.7%) and mouse (7 +/- 2%) pituitary cells. Colocalization studies with leptin and pituitary hormones showed leptin expression mainly in TSH cells (24 +/- 2% of TSH cel ls in the rat pituitary and 31 +/- 1% of TSH cells in the mouse pituitary). A folliculo-stellate (FS) cell line, TtT/GF, also expressed leptin. The lo ng isoform of leptin receptor (OB-Rb) was present in normal pituitary and i n various pituitary cell lines, including FS GH(3) and alpha T-3-1 cells. T reatment of GH(3) and FS cells with (1 x 10(-8) M) inhibited cell prolifera tion assessed by [H-3]thy-leptin midine incorporation in GH,, but not in FS , cells. These findings show for the first time that leptin is expressed in rat and mouse anterior pituitaries mainly by TSH cells and by a mouse FS cell line. The finding of leptin and of the long isoform of leptin receptor in normal rat and mouse pituitaries and in various cell lines implicates an autocrin e/paracrine loop in the production and regulation of leptin and leptin rece ptor in the rodent pituitary.