877 Original Paper Cell Physiol Biochem 2007;20:877-886 Accepted: July 04, 2007 Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology Cellular Physiology and Biochemistr and Biochemistr and Biochemistr and Biochemistr and Biochemistry Copyright © 2007 S. Karger AG, Basel Fax +41 61 306 12 34 E-Mail karger@karger.ch www.karger.com © 2007 S. Karger AG, Basel 1015-8987/07/0206-0877$23.50/0 Accessible online at: www.karger.com/cpb Sex Steroid Receptor Expression Profile in Brown Adipose Tissue. Effects of Hormonal Status Grup de Metabolisme Energetic i Nutrició. Departament de Biologia Fonamental i Ciències de la Salut. Institut Universitari d’ Investigació en Ciencies de la Salut. Universitat de les Illes Balears and Ciber Fisiopatología Obesidad y Nutrición (CB06/03) Instituto de Salud Carlos III, Palma de Mallorca, * Department of Biomaterials, Institute for Clinical Dentistry, University of Oslo Pilar Roca Departament de Biologia Fonamental i Ciències de la Salut Ed. Guillem Colom. Universitat de les Illes Balears. Cra. Valldemossa Km 7.5, Palma de Mallorca, 07122 (Spain) Tel. +34 971 173172, Fax +34 971 173184, E-Mail pilar.roca@uib.es Key Words Oestrogen receptor  Androgen receptor  Progesterone receptor  Brown adipose tissue  Gender dimorphism Abstract Recent investigations suggest that sex hormones play an important role in the brown adipose tissue (BAT) thermogenic program by acting on several steps of the lipolytic signal cascade and on the UCP1 transcription control. However, the number of studies focusing on steroid receptor status in brown adipose tissue is negligible. In the present study, we analyze steroid receptor mRNA levels in brown adipose tissue in male and female rats and in pregnant and lactating females, all of them models with a different hormonal background. The direct effect of sex hormones on the expression of their receptors was studied in vitro in primary culture of brown adipocytes. Oestrogen receptor (ERα) and androgen receptor (AR) densities were higher in male than in female BAT. PR A+B mRNA expression was downregulated in lactation, suggesting a role of progesterone signalling in thermogenesis impairment at this stage. In vitro studies showed that progesterone decreased PR A+B mRNA and that testosterone downregulated ERα mRNA. The results highlighted in this study demonstrate the presence of steroid receptor mRNA in BAT and in brown cell cultured adipocytes, supporting the idea that changes in steroid receptor expression would be important for the understanding of sex hormone effects on BAT physiology. Introduction BAT is of fundamental relevance in the regulation of energy balance and body weight control, particularly in rodents [1], as is the main mediator of adaptive ther- mogenesis, which is highly dependent on the activity of uncoupling protein 1 (UCP1). UCP1 is an inner mito- chondrial membrane protein that can dissipate energy as Sergio Rodriguez-Cuenca, Marta Monjo*, Marga Frontera, Magdalena Gianotti, Ana Maria Proenza and Pilar Roca