RESUMO
BACKGROUND: The role of creatine (Cr) and creatine kinase (CK) in sperm function remains unclear. The study aimed to assess Cr and CK in seminal plasma and test their association with sperm characteristics. METHODS: The study included 62 males with couple's infertility and 26 males who have already fathered children. Semen Cr and CK were assessed by GC-MS and spectrophotometry, respectively. Seminogram parameters were analyzed using conventional methods. RESULTS: Cytomorphologic analysis of sperm showed normozoospermia in 53 men (NS) and an asthenozoospermia (AS) in 35 men. Semen Cr was high with no significant difference between the two groups (791 ± 342 and 744 ± 422 µmol/L, respectively). However, semen CK activity was higher in AS group (1,360 ± 1,050 vs. 830 ± 580 U/L, p = 0.013). Semen Cr was positively related to progressive motility (r = 0.284; p = 0.010). Semen CK was negatively correlated with sperm concentration (r = -0.29; p = 0.01), progressive motility (r = -0.26; p = 0.03), and the percentage of abnormal spermatozoa (r = -0.28; p = 0.02). CONCLUSIONS: Semen contains high amounts of Cr and increased CK activity. Low semen Cr is associated with reduced sperm motility while high CK activity is associated with poor sperm quality. The findings suggest that Cr is of importance for sperm metabolism and that Cr supplementation could be useful in males with poor quality sperm.