Epididymal sperm transport in normal and recent spinal cord injured Sprague Dawley rats

Causes of poor semen quality following spinal cord injury (SCI) are not known. One possible reason, based upon studies that reported improved semen quality in SCI men after several induced ejaculations, is delayed epididymal sperm transport. Our study was designed to establish baseline epididymal sperm transport values in the Sprague Dawley rat and evaluate effects of SCI on this process. Spermatozoa protamine was labeled with tritiated arginine, and the rats were sacrificed various times after injection. Each epididymis was divided into six equal sections from proximal to distal. Sperm tails were dissolved with 8 molar (M) urea in the presence of 2 mM dithiothreitol (DTT); sperm heads were collected by centrifugation (3,000 rpms, 10 min.). The radioactivity in sperm heads from each section was counted and expressed as counts per million sperm heads. To account for different rates of labeled arginine incorporation, the percentage of counts per million sperm heads in each section was calculated relative to the total number of counts in all six sections. Our results showed there was an orderly progression of sperm through the epididymis. It took 8 days for labeled sperm to enter the epididymis and 28 days to peak in the caudal (tail) section in non-SCI rats. Stasis was present 10 days after T-9 SCI in rats compared with transport in sham controls. This was evidenced by a significant increase in the percentage of labeled sperm in proximal sections of the epididymis (sections 1, 2, and 4) in T-9 transected animals (p < 0.01). If similar stasis occurs in SCI men, it could obviously contribute to poor semen quality. However, it remains to be determined how long this stasis persists after SCI in rats.