Lowered levels of bicarbonate in seminal plasma cause the poor sperm motility in human infertile patients

Both the adenylate cyclase activity and the motility of human sperm were stimulated by bicarbonate with the same concentration dependency. The correlation between bicarbonate levels in semen and the motility of sperm from the patients with male infertility was investigated. Bicarbonate in semen was found to originate mainly from the seminal vesicles, and a significant positive correlation was observed between bicarbonate levels and volume of semen. The motility of infertile sperm was also found to correlate positively to the seminal levels of bicarbonate. These results suggest that the lowered levels of bicarbonate in semen are at least in part responsible for the poor sperm motility in infertile patients, as a result of the failure in the activation of sperm adenylate cyclase.