Extra-epididymal spermatozoa account for approximately a third of all sperm
atozoa found in the normal human ejaculate. Whilst remaining outside of the
testes at core body temperature, the functional competence of spermatozoa,
including cell motility and fertilizing capacity, diminishes. By examining
spermatozoa found in the seminal fluid of recently vasectomized men, this
study has investigated the nuclear changes that occur in spermatozoa whilst
persisting in sites distal to the epididymis. Spectral recordings of sperm
atozoa stained with the nucleic acid dye, toluidine blue and the sperm chro
matin structure assay (SCSA) were performed. Toluidine blue staining of hum
an sperm DNA is an effective predictor of abnormal protamine disulphide cro
sslinking and chromatin condensation. Using flow cytometry, the SCSA determ
ines the sensitivity of sperm DNA to acid-induced denaturation, providing a
measure of chromatin and DNA damage. Abnormal protamine disulphide crossli
nking and chromatin condensation was significantly higher in spermatozoa fr
om patients after vasectomy when compared to normozoospermic controls (p <
0.01). Additionally, spermatozoa from vasectomized donors were significantl
y more sensitive to acid-induced denaturation than were normozoospermic don
ors (p < 0.05). The results indicate that spermatozoa surviving in extra-ep
ididymal sites are more likely to possess DNA and chromatin abnormalities t
han those present in the testes and epididymis. These changes may partly ex
plain the depletion of cell viability and fertilizing capacity of extra-epi
didymal spermatozoa which has been reported previously.