ORIGINAL ARTICLE Microscopic Characterization of Follicular Structures in Letrozole-induced Polycystic Ovarian Syndrome in the Rat Celina Baravalle, a,b Natalia R. Salvetti, a,b Gustavo A. Mira, b Natalia Pezzone, c and Hugo H. Ortega a,b a Department of Anatomy and Histology, b Center for Experimental Biology and Laboratory Animals Sciences, c Department of Pathology, Faculty of Veterinary Sciences, National University of Litoral, Esperanza, Santa Fe, Argentina Received for publication September 27, 2005; accepted April 24, 2006 (ARCMED-D-05-00395). Background. Our objective was to characterize the tissular distribution of relevant cyto- skeletal proteins, cellular adhesion molecules and proliferation markers and conduct a his- tomorphometrical study of the follicular wall of letrozole-induced polycystic ovaries. Methods. Twenty rats were divided into two groups: a control group (C) of ten rats that received vehicle only (0.9% NaCl solution) once daily p.o. and a treatment group (T) of ten animals administered letrozole at a concentration of 1 mg/kg p.o. dissolved in 0.9% NaCl solution once daily during 21 days. Twenty four h after the last administration, all animals were sacrificed. Control animals were sacrificed in proestrous (n 5 5) and dies- trous (n 5 5). Serum hormone levels, histomorphometrical changes and immunoexpres- sion of intermediate filaments (vimentin, cytokeratins and desmin), cadherins and proliferation cellular nuclear antigen were examined. Results. The granulosa cell layer of cystic follicles had a greater significant immunostain- ing for vimentin and cytokeratins. Immunohistochemical localization of desmin was re- stricted to the theca externa. Positive immunoreactivity for cadherins rises gradually and significantly, together with the follicular development, and immunoreactivity was com- paratively stronger in follicular cysts. A significantly higher immunostaining for PCNA cells was observed in secondary and tertiary follicles as compared with atretic and cystic follicles. An increase in the LH, FSH and testosterone serum concentrations was observed in letrozole-treated rats. Estradiol and progesterone showed a considerable reduction. Conclusions. The changes observed are probably due to structural and functional alter- ations that occur during the process of cystogenesis and may be associated with important modifications in the expression of cytoskeletal proteins, cellular adhesion molecules and proliferation markers that may be essential for proper cellular functioning. Ó 2006 IMSS. Published by Elsevier Inc. Key Words: Letrozole, Intermediate filaments, Cadherins, Cellular proliferation, Ovary, Polycystic ovarian syndrome, Rat. Introduction Polycystic ovarian syndrome (PCOS) is the most common endocrine disorder affecting women of reproductive age. It is considered to be a syndrome and not a disease, although the term polycystic ovarian disease is often used synonymously, but incorrectly, to describe the syndrome manifested by heterogeneous clinical features (1). Numerous experimental models for PCOS have been developed in rats. The following hormonal substances, among others, have been employed to induce that syn- drome: estradiol valerate, dehydroepiandrostenerone, and neonatal androgenization (2,3). In spite of their effective- ness, all these hormonal treatments cause a sudden appear- ance of polycystic ovaries due to disturbances in the Address reprint requests to: Dr. Hugo H. Ortega, Department of Anat- omy and Histology, Faculty of Veterinary Sciences, National University of Litoral, R.P. Kreder 2805. (3080) Esperanza, Santa Fe, Argentina; E-mail: hhortega@fcv.unl.edu.ar 0188-4409/06 $–see front matter. Copyright Ó 2006 IMSS. Published by Elsevier Inc. doi: 10.1016/j.arcmed.2006.04.006 Archives of Medical Research 37 (2006) 830–839