Fertilization potential and qualitative characteristics of human spermatozoa after short-term cryostorage at 5 degrees C in two different TEST-yolk buffer preparations.

Use of the media TEST-yolk buffer (TYB) in semenology today enables the short-term incubation and cryostorage of spermatozoa and its subsequent use in the various assisted reproductive technologies (ART). Preparation of TYB media involves the addition of egg yolk (20% v/v) to a physiological solution of the zwitterion buffers TES and Tris. The TYB is usually thermoprecipitated to remove the majority of the egg yolk globules and other macromolecules from the medium. However, removal of these egg yolk constituents could possibly eliminate or reduce essential factors that could enhance the sperm viability and fertilization potential after short-term dilution and storage. Improvements in the quality of the TYB could add greater benefits to those techniques employed in the various forms of ART. The objectives of the investigation were 1) to study the sperm qualitative characteristics following short-term cryostorage at 5 degrees C in either thermoprecipitated (T-TYB) or non-thermoprecipitated (NT-TYB), and 2) to compare the fertilizing potential of spermatozoa stored for 24 hours at 5 degrees C in the two TYB preparations. In Experiment 1, semen specimens from 15 patients were collected, assessed and split into two aliquots. Sperm specimens were processed by diluting 1:1 (v/v) with the T-TYB or NT-TYB, followed by centrifugation and reconstitution of the specimen to its initial volume with the corresponding TYB medium. Sperm specimens were cryostored for 1, 2, 24, 48 and 72 hours. Samples were taken at each interval and placed in a 37 degrees C water bath and allowed to warm for 15 minutes after each cryostorage interval. Semen specimens were assessed for percentage and grade of motility. The results of this study indicated that, although the NT-TYB yielded better results than the T-TYB, overall those differences were not statistically significant. In Experiment 2, the fertilization potential of spermatozoa recovered after 24 hours of cryostorage in the two TYB preparations and further prepared via filtration, was assessed by the sperm penetration assay (SPA) using zona-free hamster oocytes. The average penetration rate (PR) and penetration index (PI) were significantly better for the NT-TYB than for the T-TYB. The PR was 54% vs. 25%, and the PI 0.78 and 0.27 for spermatozoa incubated in the NT-TYB vs. T-TYB. The range of penetration was also much lower for the T-TYB (6 to 100%) preparation when compared to the NT-TYB (22 to 100%). The highest penetrator showed 100% for both preparations. However, the lowest penetrator showed 6% for the T-TYB and 22% for the NT-TYB. The data obtained in this study suggest that both TYB preparations can be employed in short-term cryostorage (5 degrees C) of human spermatozoa and can adequately maintain the qualitative characteristics of those spermatozoa. The data also showed that the NT-TYB preparation yielded sperm samples of higher fertilization potential, thus possibly establishing the superior usefulness of the NT-TYB in an ART program.