Activity of testis angiotensin converting enzyme (ACE) in ejaculated humanspermatozoa

Testicular angiotensin converting enzyme (ACE) isozyme is likely to play im portant functional roles in male reproduction. Several studies have shown t hat ACE is released from human spermatozoa during capacitation and that ACE is associated with reduced sperm motility. Recently, we established an ass ay to detect testicular ACE activity in human spermatozoa. The purpose of t his study was to determine if testicular ACE activity is related to sperm m otility in human ejaculates. Semen samples were collected from 80 infertile patients. According to the semen characteristics, they were divided into f our (WHO) categories. Enzyme activities of ACE in spermatozoa (testicular A CE) and seminal plasma (somatic ACE) were spectrophotometrically determined . Total testicular ACE activity in spermatozoa was measured by solubilizati on of spermatozoa with Triton X-100. Membrane testicular ACE activity was m easured in a sperm : PBS suspension. Sperm concentration and sperm motility were 136.6 +/- 154.1 x 10(6)/mL and 58.6 +/- 23.4%, respectively (mean SID ). Enzyme activities of membrane testicular ACE, total testicular ACE and s omatic ACE were 0.273 +/- 1.219 muU/10(6) spermatozoa, 0.35 +/- 1.34 muU/10 (6) spermatozoa and 684.7 +/- 226.6 mU/mL, respectively. A negative correla tion was observed between sperm motility and membrane testicular ACE activi ty (p < 0.05). Membrane testicular ACE activity in 44 normal semen samples was 0.04 <plus/minus>0.02 muU/10(6) spermatozoa, whilst that in 36 abnormal semen samples was 0.24 +/- 0.42 muU/10(6) spermatozoa. There was a signifi cant difference between these two groups (p < 0.01). Membrane testicular AC E in sperm samples from normozoospermic men was significantly lower than th at from oligoasthenozoospermic men (P < 0.05). These findings suggest that testicular ACE is released from normal functional spermatozoa for them to h ave fertilizing ability.