1 23 Endocrine International Journal of Basic and Clinical Endocrinology ISSN 1355-008X Endocrine DOI 10.1007/s12020-013-9905-2 Cross-sex hormonal replacement: is this really effective? an experimental clue Natalia Pavón, Israel Pérez-Torres, Alberto Aranda, Francisco-Javier Roldán, Cristina Paredes & Edmundo Chávez