LOCALIZATION OF LEPTIN RECEPTOR (OB!R) IN THE SKIN OF RUMINANTS: AN IMMUNOHISTOCHEMICAL STUDY.

receptor superfamily (1). It is highly expressed in the hypothalamus although its expression has also been demonstrated in many peripheral tissues. Leptin is a polypeptide mainly secreted by adipose tissue, regulating appetite and energy consumption (2). However Ob!R distribution suggests that leptin might exert diverse biological functions other than energy metabolism regulation. Accordingly, leptin acts as a mitogen for a large number of cell types, including the epidermis where it has been detected together with its receptor. In particular, leptin strongly stimulates a proliferative response of keratinocytes during skin repair (3). Leptin and its receptor have also been detected in human and mouse hair follicle (HF) and an involvement of leptin in the control of HF morphogenesis has been suggested (4, 5). The aim of this work is to study the presence of Ob!R and to localize it in the skin of ruminants. Skin samples, collected from the dorsal region of healthy animals, were fixed in 10% neutral!buffered formalin and embedded in paraffin wax. Dewaxed sections were microwaved in 10 mM citric acid (pH 6.0) for antigen retrieval and endogenous peroxidase activity was quenched with a peroxidase!blocking solution (3% H2O2). Subsequently, the slides were incubated with 1:100 goat polyclonal anti Ob!R antibody (Santa Cruz Biotechnology) for 24 hours. After incubation with 1:200 horse anti!goat biotin conjugate antibody (Santa Cruz Biotechnology), the reaction was visualized with the Vectastain ABC kit and revealed with DAB. The immunohistochemical investigation allowed us to evidence a clear positivity of Ob!R in some components of ovine and bovine skin. In both species, cytoplasmic staining was observed in the cells of the outer root sheath of the HF at the level of the isthmus and the soprabulbar region. The signal was present in both growing and regressive phase HF. As regards sheep, Ob!R positive cells were also observed in the basal layer of the epidermis. At present, leptin is considered one of the major players in the biology and pathology of mammalian skin and its appendages. In humans, it represents a novel therapeutic factor to improve severely disturbed wound!healing conditions. The identification of Ob!R in the skin of ruminants represents an important goal to understand the biological mechanisms involving this molecule with implications in the clinical field