Effect of seminal plasma proteins on membrane cholesterol efflux of ram epididymal spermatozoa

- Cholesterol has a key role in permeability, fluidity and organizing the membrane lipids of sperm.
- Cholesterol content of plasma membrane have important role in resistance of sperm against cold shock.
- Cholesterol efflux of sperm membrane will be evaluated in ram epididymal spermatozoa following incubation with seminal plasma protein for 4 h at 37 °C.
- For first time, we showed that seminal plasma proteins induce cholesterol efflux from ram epididymal spermatozoa.

This experiment was conducted to determine the effect of seminal plasma protein (SPP) on the membrane cholesterol efflux of ram epididymal spermatozoa. To obtain epididymal spermatozoa, testes of five healthy mature rams were collected from slaughterhouse in five times. Epididymal spermatozoa were split into three groups and it was added 0, 0.3 and 0.6 mg/ml SPP and control group (containing 0.6 mg/ml SPP without sperm) was included. Each group was split into three subgroups and incubated at 37 °C. Sperm motility, viability and functional membrane integrity were evaluated after 0, 2 and 4 h incubation. At 4 h, a sample was centrifuged by 10,000 × g at 4 °C for 10 min and the concentration of cholesterol was determined in supernatant by gas chromatography. The main effect of seminal plasma protein showed that sperm motility was highest at 0 mg/ml SPP (66.33%; P < 0.05) and there was no difference between 0.3 (56.70%) and 0.6 mg/ml SPP (53.33%; P > 0.05). The highest and lowest functional membrane integrity were observed at 0 (84.00%) and 0.6 mg/ml SPP (77.13%), respectively (P < 0.05). Sperm viability was higher at 0 mg/ml SPP (87.27%) than 0.6 mg/ml SPP (84.47%; P < 0.05) and there was no difference between 0.3 (85.87%) and 0.6 mg/ml SPP (P > 0.05). The concentration of cholesterol was highest at 0.6 mg/ml SPP (3.95 μg/100 × 106 sperm) and lowest at 0 mg/ml SPP (0.1 mg/100 × 106 sperm) and control (0.0 mg), respectively (P < 0.05). Therefore, seminal plasma proteins induced cholesterol efflux from ram epididymal spermatozoa.