Effect of preincubation of human spermatozoa in milk on penetration of zona-free hamster oocytes: comparison to TEST yolk

Influence of media and thermal shock on sperm capacitation

To elucidate the influence of medium and thermal shock in inducing sperm capacitation, eight ejaculates were processed as follows. Each ejaculate was divided into three aliquots. To two of the aliquots, an equal volume of saline was added, while TEST-yolk was added to the remaining aliquot. All three samples were cooled slowly to 5 degrees C and incubated for 18-20 h. After aspirating the supernatant, 6 ml of Tyrode solution containing 0.06 g% egg yolk, warmed to 37 degrees C was added without disturbing the sperm pellet to the aliquot containing TEST-yolk and to one of the aliquots mixed with saline. To the remaining saline-processed sperm pellet, 6 ml TEST-yolk (37 degrees C) was added. All samples were washed twice (400 x g for 5 min) and processed for the sperm penetration assay (SPA). Samples, either pre-incubated in TEST-yolk (mean +/- SEM; 65.9 +/- 11.7%) or warmed (thermal shock) with TEST-yolk (62.6 +/-12.1%) yielded significantly (P < 0.05) higher SPA outcome than the samples processed and warmed with saline (17.8 +/- 12.0%). The penetration indices were not statistically different from each other. It therefore appears that the medium influences the sperm capacitation process to a greater extent and may augment the influence of thermal shock.

Milk versus TEST-yolk--preincubated sperm; in vitro fertilization outcome

OBJECTIVE

Preincubation of sperm in TEST-yolk medium enhances in vitro fertilization (IVF) outcome. However preincubation of sperm in milk at 5 degrees C enhances the results of sperm penetration assay and hemizona assay. This study was therefore performed to determine the influence of milk on in vitro fertilization rate of human oocytes, as compared with TEST-yolk medium.

STUDY DESIGN

Forty-one consecutive couples undergoing an IVF procedure were randomized. Of these 20 couples were admitted for the milk study (group 1) and 21 couples for the TEST-yolk study (group 2). Each ejaculate was Percoll-processed and the sperm pellet was resuspended in 0.5 ml of culture medium. An equal volume of heat-inactivated homogenized cow's milk (95 degrees C, 10 min) was added to sperm suspension from group 1 and an equal volume of TEST-yolk medium was added to sperm suspension from group 2. After 2 h of incubation at 5 degrees C and washing with culture medium at 37 degrees C, oocytes were inseminated. Oocytes from group 1 couples were inseminated with milk-treated spermatozoa and those from group 2 couples with yolk-treated spermatozoa. Oocytes were evaluated for fertilization after 18 h.

RESULTS

Sperm preincubated in milk fertilized 75 out of 100 mature oocytes (75%). TEST-yolk-treated sperm fertilized 45 out of 64 mature oocytes (70%). The difference was not statistically significant.

CONCLUSIONS

Preincubation of spermatozoa in milk, as compared with preincubation in TEST-yolk medium yields a similar IVF outcome, so milk may be a suitable alternative medium for preincubation of spermatozoa to enhance its fertilizing potential.

Effect of milk-yolk on the fertilizing capacity of spermatozoa

Pre-incubation of human sperm in egg yolk based medium (TEST-yolk) as well as milk have been shown to improve sperm fertilizing capacity. The purpose of this study was to compare a combination of these two media, called milk-yolk, against the two established media, in order to test for a possible synergistic effect(s) on sperm functions as measured by sperm motility, acrosome reaction and penetration assay. Statistically, no differences have been observed among the three media, except for SPA outcome in milk-yolk, being significantly lower than the corresponding values for the other two media. In conclusion the beneficial effects of egg yolk and milk appear to be eliminated once both media are combined, resulting in an antagonistic effect on the fertilizing capacity of the spermatozoa.