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Leptin and Leptin Receptor Expression in Rat and Mouse Pituitary Cells¹

Department of Laboratory Medicine and Pathology (L.J., S.Z., M.E.C., E.K., R.V.L.), and Endocrine Research Unit (B.G.B.), Mayo Clinic, Rochester, Minnesota 55905; and Tokai University School of Medicine (R.Y.O.), Isehara City, Japan

Address all correspondence and requests for reprints to: Dr. Ricardo V. Lloyd, Mayo Clinic, Department of Laboratory Medicine and Pathology, 200 First Street SW, Rochester, Minnesota 55905.

Leptin is a circulating hormone secreted mainly by adipose tissue. Recent studies have shown leptin production by other tissues, including the placenta, stomach, and mammary tissues. Various reports have suggested that the anterior pituitary may have a role in the regulatory effects of leptin. We recently localized leptin in the human anterior pituitary, but analysis of leptin 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 messenger 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 cells 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 long isoform of leptin receptor (OB-Rb) was present in normal pituitary and in various pituitary cell lines, including FS, GH₃, and T₃-1 cells. Treatment of GH₃ and FS cells with leptin (1 x 10^-8 M) inhibited cell proliferation assessed by [³H]thymidine incorporation in GH₃, 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 autocrine/paracrine loop in the production and regulation of leptin and leptin receptor in the rodent pituitary.