Abstract
To investigate whether the fertilizing ability is changed during transit of spermatozoa in the cauda epididymis in BALB/c mouse which is known as a low in vitro fertilization (IVF) rate, we examined the capacitation rates of spermatozoa collected from 3 regions of the cauda epididymis by chlortetracycline (CTC) fluorescence assay. In addition, their fertilizing ability was examined by IVF with cumulus-intact and cumulus-free mouse eggs. Spermatozoa immediately collected from the cauda epididymis showed no significant differences in capacitation rates (the proportion of spermatozoa having a fluorescence-free dark band in the postacrosomal region; B pattern) estimated by CTC test among regions. Nevertheless, the capacitation rates in the proximal region were significantly (P<0.05) higher than that in distal region at 60 min of incubation and the middle region at 120 min of incubation. Non-preincubated spermatozoa regardless of the collection regions in the cauda epididymis showed signs of low fertilizing ability in cumulus-intact (9-10%) and cumulus-free (0-4%) mouse eggs at 6 h after insemination. After 2 h sperm preincubation, fertilization rates of spermatozoa collected from the proximal and distal regions were only slightly increased (26-44%) but that of middle region was greatly increased in both cumulus-intact (68%) and cumulus-free (61%) mouse eggs. These results suggest that the fertilizing ability of BALB/c mouse spermatozoa is changed during transit of the cauda epididymis, and the spermatozoa in the middle region of the cauda epididymis could be utilized efficiently for IVF in the BALB/c mouse strain.
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