202FERTILIZING ABILITY OF EPIDIDYMAL CAT SPERMATOZOA AFTER CRYOPRESERVATION OR STORAGE AT 4°C.

Abstract

The possibility of harvesting cat epididymal spermatozoa from excised testis represents a potentially important tool for preserving valuable genetic material from males that die unexpectedly. The purpose of this study was to evaluate plasma membrane integrity, acrosomal status and in vitro fertilizing capability of epididymal cat sperm after short- and long-term storage at 4°C and after cryopreservation. Spermatozoa were collected by flushing the cauda epididymis and the vasa deferentia removed from adult cats undergoing orchiectomy. Spermatozoa were split into three aliquots: A-fresh, B-frozen, and C-cooled. The A portion was immediately tested on the day of collection (control), the B portion was frozen in pellets in Test Yolk Buffer (TYB) with 8% glycerol, while the C portion was extended in TYB and stored at 4°C for 1 day, 2 days or 7 days. Cat oocytes recovered from minced ovaries were matured for 24h in TCM 199+1UI/mL hCG+0.5UI/mL FSH+0.3% BSA at 38.5°C in 5% CO2. In vitro fertilization (IVF) of in vitro-matured (IVM) oocytes was performed using spermatozoa from portions A, B or C in modified Tyrode’s solution supplemented with 0.6% BSA at 38.5°C in 5% in air. Before IVF, aliquots of sperm samples from the three portions were stained simultaneously with fluorescein isothiocyanate-labelled Pisum Sativum agglutinin (FITC-PSA) and propidium iodide to evaluate the percentage of plasma membrane-intact spermatozoa with acrosomes present. At least 200 spermatozoa were counted in duplicate for each sample. After 24h of incubation, to evaluate fertilization rate, the oocytes were stained with aceto-lacmoid. Oocytes with two pronuclei, presumably male and female, were classified as fertilized. The percentages of spermatozoa maintaining plasma membrane integrity and intact acrosomes after 1 day or 2 days of storage at 4°C were 75% and 65%, respectively, and were similar to that of fresh epididymal spermatozoa (78%). However, the percentages of spermatozoa with intact plasma membranes that had intact acrosomes after 7 days of storage at 4°C (52%) or after cryopreservation (48%) were significantly lower (P<0.01, ANOVA) than those of samples stored for 1 or 2 days at 4°C. As shown in the Table, fertilization rates of oocytes inseminated with fresh spermatozoa and spermatozoa stored for 1 or 2 days were similar. In contrast, the fertilization rates of oocytes inseminated with spermatozoa that had been cryopreserved or stored for 7 days were significantly lower than those obtained with spermatozoa used immediately after collection or storage for 1 day. From our results, we suggest that storage of epididymal spermatozoa at 4°C may be a potentially useful method for temporary storage of spermatozoa from endangered cats, and may allow more efficient use and long-distance transport of genetically important germplasm. This work was supported by MIUR (ex 40%). Table 1 In vitro fertilization of in vitro-matured cat oocytes with fresh, stored at 4°C and cryopreserved epididymal cat spermatozoa