IMMUNOLOCALIZATION OF LEPTIN AND ITS RECEPTOR IN THE SWEAT GLAND AND SEBACEOUS GLAND OF THE HORSE.

Leptin (Ob) is a hormone primarily secreted by adipocytes of subcutaneous and visceral fat which binds to a specific receptor (Ob-R). It is considered an important factor involved in the skin biology. Ob plays a critical role in the regulation of wound healing processes (1) and it seems to be involved in the control of hair follicle cycle (2) as well as in the biology of sebaceous gland (3). The study of Ob in the skin of domestic animals can be of great importance to improve our knowledge in the biology of the integumentary system. We recently identified the Ob-R in the skin of some domestic animals such as dog, sheep and cow. The aim of this work is to continue this investigation by evaluating the presence of Ob and its receptor in the skin of the horse. Normal skin samples, collected from five animals, were fixed in 10% neutral-buffered formalin. Skin sections were microwaved in 10 mM citric acid (pH 6.0) for antigen retrieval. The endogenous peroxidase activity was blocked with 3% peroxidase-blocking solution and non-specific binding was blocked with normal goat serum. The sections were incubated with mouse monoclonal anti Ob (Fitzgerald) or goat polyclonal anti Ob-R (Santa Cruz Biotechnology) antibody for 24 hours and, successively, they were incubated with the goat anti-mouse or goat anti-rabbit biotin conjugate antibody, respectively. The reaction was detected with the Vectastain ABC kit and visualized with diaminobenzidine. By observing immunohistochemical treated sections, we evidenced an intense positivity to both Ob and its receptor in the cells of the apocrine sweat glands in all subjects considered. Moreover, leptin receptor positivity was observed in the basal cells of sebaceous glands. The staining for Ob was localized in the cytoplasm of the cells while the staining for Ob-R was both in the cell cytoplasm and membrane. No staining was observed in other structures of skin. The result obtained suggests a role of Ob in the regulation of the sweat and sebaceous gland activity. Apocrine sweat gland cells are both source and target of leptin then, an autocrine or paracrine control by the hormone can be supposed. Since the cells of sweat glands express only the leptin receptor, it is likely an endocrine control by the leptin on sweat glands according to Chen et al., (2002)