1102 Int. J. Morphol., 33(3):1102-1107, 2015. Effects of Nandrolone Decanoate on Spermatogenesis in Wistar Rats With and Without Physical Training Efectos del Decanoato de Nandrolona sobre la Espermatogénesis en Ratas Wistar con y sin Entrenamiento Físico Bernardo Porto Maia * ; Jéssica de Oliveira Silveira * ; Mariana Garcia Lisboa Borges * ; Danilo Ales Ponzi Pereira * ; Julyara Lima Pinheiro * ; Jofre Jacob da Silva Freitas ** & Katia Simone Kietzer ** MAIA, B. P.; SILVEIRA, J. O.; BORGES, M. G. L.; PEREIRA, D. A. P.; PINHEIRO, J. L.; FREITAS, J. J. S. & KIETZER, K. S. Effects of nandrolone decanoate on spermatogenesis in Wistar rats with and without physical training. Int. J. Morphol., 33(3):1102-1107, 2015. SUMMARY: Androgenic anabolic steroids (AAS) are artificial testosterone analogues, used as medicine in chronic diseases, because they increase protein synthesis generating muscle hypertrophy. Its effect has caught the attention of athletes and gym users, thus their consumption has become epidemic, due to easy marketing, the immediate results and the false impression that it doesn’ t carry health risks. Such risks may globally harm the body. This study aims to investigate the influence on spermatogenesis of using nandrolone decanoate with or without physical training. Twenty-four rats, divided into four groups were used: sedentary group (SG), sedentary on steroids group (SSG), trained group (TG) and trained on steroids group (TSG). The animals were trained on voluntary exercise wheel twice a week during 12 weeks, and were subsequently euthanized by decapitation. Groups TSG and SSG received intramuscular injections of 5 mg / kg of the AAS. It was found that there was a greater cellularity in TSG, suggesting interference between androgen therapy and physical training on the mount of cells in the seminiferous epithelium. Comparing the TSG group with the SG, it is noticed that the physical training associated with the use of steroid tends to affect cell division without compromise, however, the number of spermatogonia, did not significantly vary compared to the control group. Finally, it seems that there was no significant statistical difference among the groups in terms of spermatogenesis yield, so that can not be said that the use of nandrolone decanoate, with or without the physical training, interfere with fertility. KEY WORDS: Spermatogenesis; Anabolic agents; Nandrolone ; Exercise; Fertility. INTRODUCTION Androgenic anabolic steroids (AAS) are artificial testosterone analogues, produced by testicles (90%) and adrenal glands (10%). They are responsible for male characteristics development (androgyny) and for the lean tissue synthesis (anabolism), being used as medicine in chronic diseases, because they increase protein synthesis generating muscle hypertrophy (Kang et al., 2014; Koike, 2010; Smith & Walker, 2014). Due to the remarkable anabolic effect, mainly in muscle tissue, the AAS are being widely used by individuals to improve their athletic performance or bodily appearance. Besides the hypertrophy of skeletal muscle mass, these substances also promote androgenization, stimulating masculinizing characteristics in both men and women (Boff, 2010; de Paiva Foletto et al., 2010). Nandrolone decanoate (ND), also known as Deca- Durabolin® and developed by Organon Laboratory in 1962, presents characteristic of being more anabolic than androgenic, which is why it became one of the most used AAS in the world (Oliveira et al., 2012). It is also one of the most used AAS in gyms for beauty purposes (de Paiva Foletto et al.) and it is widely used in the clinical medicine (Oliveira et al.). Among the many side effects of hormonal therapy with AAS, are: heart problems, disorders of the adrenal glands, aggressive behavior, increased risk of prostate cancer, problems related to a lack of libido and impotence. Beside its influence on the prostate and libido, AAS seems to directly affect the testicles and their functions. It is known that several species of experimental animals evolved * Universidade do Estado do Pará, Belem, Brazil. ** Laboratório de Morfofisiologia Aplicada a Saúde, Universidade do Estado do Pará, Belem, Brazil.