Objective: Preclinical and very limited clinical studies suggest that sildenafil may have therapeutic potential in selected neurological disorders. However, many neurological side effects of sildenafil have been reported. This work aimed to clarify the histopathological effect of sildenafil citrate on the superior colliculus (SC) of adult male albino rat.
Material and methods: 24 adult male albino rats were used and divided into 4 groups. The first 3 groups were received respectively sildenafil citrate orally at doses 0.25, 0.70 and 1.43mg/kg body weight daily for 30 days while the 4th group was used as control. At end of the treatment, the superior colliculi were undergone light and electron microscopic investigation.
Results: In the control group, superficial part of the SC has neural cells and myelinated nerve fibers. With least dose of sildenafil, the superficial part of SC revealed disturbance in neural tissue with dilated capillaries and vacuoles. Some neurons showed deeply stained nuclei shrunken cytoplasm. Some cells showed enlarged mitochondria and dilated endoplasmic reticulum. With medium dose of sildenafil, SC showed more disturbances; stripped myelin sheaths or widely separated myelin lamellae, dilated blood vessels with large vacuoles around them and many neurons with apoptotic criteria. However, maximum dose of sildenafil induced massive destruction of edematous neural tissue; invasion of the surface with massive blood vessels, marked decrease in thickness of myelin sheaths and the neural cells revealed degenerative and apoptotic changes. The mean number and size of cells revealed significantly progressive decrease in all treated rats with increasing doses of the drug.
Conclusion: Long-term, daily use of sildenafil can lead to pathological effect in the superior colliculus which may be implicated in visual disturbance and this effect is dose dependent, so neurological effect of sildenafil necessitates further investigations.
Key words: sildenafil citrate, superior colliculus, angiogenesis, phosphodiesterase type 5(PDE5), apoptosis.