Journal of Cell and Animal Biology Vol. 3 (7), pp. 107-112, July, 2009 Available online at http://www.academicjournals.org/JCAB ISSN 1996-0867 © 2009 Academic Journals Full Length Research Paper Unbiased stereological and histological study of silymarin effects on hamster adrenocortical structure in response to an exogenous glucocorticoid Hamidian, Gh. 1* , Alboghobeish, N. 1 , Najafzadeh Varzi, H. 2 and Esmaeilzadeh, S. 3 1 Department of Histology, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Iran. 2 Department of Pharmacology, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Iran. 3 Department of Pathology, Faculty of Veterinary Medicine, Shahid Chamran University of Ahvaz, Iran. Accepted 9 July, 2009 Adrenal cortex is an essential portion for life and its function can be affected by many chemical agents and drugs. In this investigation, effect of silymarin, a flavonoid, on adrenocortical structure of male dexamethasone (Dexa) treated hamsters were studied by histological and unbiased stereological techniques. The results showed that the adrenal gland mass of Dexa treated hamsters was significantly decreased in comparison to animals that received Dexa with silymarin (Sily). It was also obtained that there are no significant difference in the zona glomerulosa (ZG) volume and cell number among examined groups. The volume of the cortex, zona fasciculata (ZF) and zona reticularis (ZR) and cell number of these regions were significantly reduced in Dexa treated hamsters compared to controls (P<0.05), whereas in Dexa + Sily treated animals, this reduction was not observed. Histological results showed that tissue structure of ZF and ZR was same in all groups except Dexa treated animals. In the hamster that received Dexa, a sever hyperemia was observed in the adrenal cortex. Finally it can be concluded that silymarin seem to be a suitable protective drug for side effect of glucocorticoid therapy in adrenal glands. Key words: Adrenal cortex, dexamethasone, hamster, glucocorticoid, silymarin, unbiased stereology. INTRODUCTION Pivotal role and key function of the adrenal gland in dif- ferent stages of life caused to it is called a biological clock (Pawlikowski, 2005). The adrenal gland consists of two ontogenetically, structurally and functionally distinct endocrine tissues, the cortex and the medulla. The me- dullary cells are of neurodermal origin, whereas the corti- cal ones are of mesodermal origin (Mitani et al., 1999). The adrenal cortex is necessary to life in a variety of es- sential factors and its hormones influence numerous es- sential processes (Banks, 1993; Leeson et al., 1988). Adrenal is one of the most common endocrine organs af- fected by chemically induced lesions (Ribelin, 1984). It is especially important to understand the structure and func- tion of the adrenal gland to correctly interpret the signifi- cance and mechanisms of drug-induced lesions (Rosol et *Corresponding author. E-mail: ghamidian@yahoo.com. Tel.: +98 (611) 3330073, +989113272677. Fax: +98 (611) 3360807. al., 2001). On the other hand, adrenal insufficiency may be difficult to differentiate from other same conditions, such as chronic fatigue syndrome and depression. So, in- vestigation of adrenal biology appears to be very impor- tant (Schimmer and Parker, 2001). Glucocorticoid hormones influence the activity of al-most every cell in the body; they modulate the expression of approximately ten percent of human genes (Bucking- ham, 2006). Glucocorticoids and a variety of synthetic glucocorticoid agonists are able to control carbohydrate, protein and lipid metabolism and to regulate immune and cardiovascular functions. But in therapeutic concentra- tions, glucocorticoids are strongly immunosuppressive and anti-inflammatory, which has made them one of the most frequently prescribed drugs worldwide (Schmidt et al., 2004) and glucocorticoid therapy is the most common cause of adrenal failure (Cunha et al., 2004). Further- more, it has been observed that dexamethasone treat- ment caused rapid adrenal atrophy (Mughal et al., 2004). Silymarin is a mixture of polyphenolic flavonoids ex