Brasil.3Departamento de Morfologia e Fisiologia Animal, Universidade Federal Rural de

Sildenafil (Viagra, Pfizer Pharmaceuticals) is an orally active, potent, and selective Phosphodiesterase type 5 (PDE5) inhibitor. PDE5 is the major PDE subtype responsible for cGMP hydrolysis, and it is abundant in the pulmonary vasculature [1]. The therapeutic use of this drug in pulmonary hypertension improves the pulmonary vascular haemodynamics and therefore the exercise capacity of patients [2]. The treatment involves the administration of high doses daily, and until now, little is know about the action of this scheme on testis cells. Recently, the expression of PDE5 was detected on Leydig and myoid cells of pre-pubere and adult rat testis [3]. Then, it is necessary to investigate if compounds that interfere on PDE5 activity could affect the testicular physiology. In the present study, we report several morphological alterations of mice Leydig cells after treatment with the phosphodiesterase inhibitor type 5. Twenty Swiss albino mice, 21-day-old and weighting 14-18g, were used in all experiments. Mice were examined for health status and acclimated to the laboratory environment at 25ºC and 12h light: 12h dark photoperiod. The animals were housed in metal cages and fed with a standard laboratory diet. One experimental group composed by ten animals received 25mg/kg body weight of Sildenafil for 4 weeks administered in the drinking water, and the dose was monitored by daily weighing of the water bottle. The control group, also composed by ten animals, received only pure water. After treatment the experimental and control animals were killed and pieces of testis were quickly excised with a scalpel and fixe