Aim: To study the effect of piperine on the epididymal antioxidant system of adult male rats.
Methods: Adult male rats were orally administered piperine at doses of 1 mg/kg, 10 mg/kg and 100 mg/kg body weight each day for 30 consecutive days. Twenty-four hours after the last treatment, the rats were weighed and killed with ether and the epididymis was dissected from the bodies. Sperm collected from the cauda region of the epididymis was used for the assessment of its count, motility and viability. Caput, corpus and cauda regions of the epididymis were separated and homogenized separately to obtain 10 % homogenates. The supernatants were used for the assays of sialic acid, superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, lipid peroxidation and hydrogen peroxide generation.
Results: Body weight of the piperine-treated rats remained unchanged. The weights of the caput, corpus and cauda regions of the epididymis significantly decreased at dose of 100 mg/kg. Epididymal sperm count and motility decreased at 10 mg/kg and 100 mg/kg, and sperm viability decreased significantly at 100 mg/kg. Sialic acid levels in the epididymis decreased significantly at 100 mg/kg while significant decrease in the cauda region alone was observed at 10 mg/kg. A significant decline in the activities of superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, along with an increase in hydrogen peroxide generation and lipid peroxidation were observed at 10 mg/kg and 100 mg/kg.
Conclusion: Piperine caused a decrease in the activity of antioxidant enzymes and sialic acid levels in the epididymis and thereby increased reactive oxygen species levels that could damage the epididymal environment and sperm function.
Keywords: piperine, epididymis, reactive oxygen species, antioxidant enzymes, sialic acid

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