Modulation of smooth muscle cell function: Morphological evidence for a contractile to synthetic transition in the rat ventral prostate after castration Patricia Simone Leite Vilamaior a,b , Sebastia˜o Roberto Taboga c, * , Hernandes F. Carvalho a a Department of Cell Biology, UNICAMP, Campinas, SP, Brazil b Universitary Center of Rio Preto e UNIRP, Sa ˜o Jose ´ do Rio Preto, SP, Brazil c Sa ˜o Paulo State University e IBILCE/UNESP, Department of Biology, Laborato ´rio de Microscopia e Microana ´lise, Rua Cristo ´va ˜o Colombo, 2265 e Jardim Nazareth, 15054-000 Sa ˜o Jose ´ do Rio Preto, SP, Brazil Received 8 October 2004; revised 3 May 2005; accepted 16 May 2005 Abstract In this study, we evaluated the involvement of rat ventral prostate smooth muscle cells (SMC) in secretory activity and whether this function is modulated after castration. Cell morphology was examined at both light and electron microscopy levels and the organelles involved in secretory function were labeled by the zinc-iodide-osmium (ZIO) method at the ultrastructural level and their volume density was determined by stereology. Castration resulted in marked changes of the SMC, which adopted a spinous aspect and abandoned the layered arrangement observed in the prostates of non-castrated rats. The volume density of ZIO reactive organelles increased progressively after castration, reaching significantly higher levels 21 days after castration. Since previous studies have demonstrated that SMC express SMC markers (even 21 days after castration) and are able to respond to adrenergic stimulation, we concluded that differentiated SMC are able to shift from a predominantly contractile to a more synthetic phenotype without changing their differentiation status. Ó 2005 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved. Keywords: Androgen deprivation; Castration; Smooth muscle cell; Rat ventral prostate 1. Introduction The smooth muscle cells (SMC) are predominant cell type in the prostate stroma. Its primary function is organ contraction during ejaculation, allowing the accumulated secretion to be ejected to the urethra. Interest in the SMC is twofold. Firstly, this cell is the main one responsible for benign prostatic hyperplasia (BPH), the main symptom of which is urethral obstruction and intense pain, released by the use of anti-adrenergic therapy. Secondly, SMC have been implicated in paracrine regulation of epithelial structure and function, producing key regulatory factors re- sponsible for organ homeostasis. Imbalance in these paracrine interactions with the epithelium would result in abnormal growth of either epithelium (such as in prostatic intraepithelial neoplasias and adenocarcino- mas) or SMC (as occurs in BPH) (Cunha et al., 1996). The SMC phenotype changes in response to physi- ological and pathological conditions regardless of their location. In this process, the primarily contracting cell is * Corresponding author. Tel.: C55 17 2212386; fax: C55 17 2212390. E-mail address: taboga@bio.ibilce.unesp.br (S.R. Taboga). 1065-6995/$ - see front matter Ó 2005 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.cellbi.2005.05.006 www.elsevier.com/locate/cellbi Cell Biology International 29 (2005) 809e816