Development of a simple sperm cryopreservation model using a chemically defined medium and goat cauda epididymal spermatozoa

This investigation was carried out to develop a simple sperm cryopreservati on model using a chemically defined synthetic medium (modified Ringer's sol ution) and mature goat cauda epididymal sperm as the model system. Rates of cooling, freezing, and maximum freezing temperature were manipulated with the help of a computer-controlled programmable biofreezer. Highly motile go at cauda sperm dispersed in a modified Ringer's solution was subjected to t he freezing protocol: cooling 0.25 degrees C min(-1) to 5 degrees C, 5 degr ees C min(-1) to -20 degrees C, 20 degrees C min(-1) to -100 degrees C, pri or to plunging into liquid nitrogen. In the absence of any cryoprotective a gent, all of the spermatozoa lost their motility. Addition of glycerol (0.2 2 to 0.87 M) caused a dose-dependent increase of sperm motility recovery. T he highest recovery of forward and total motility was (32 and 35%, respecti vely) at 0.87 M. Further increase of the glycerol concentration caused a ma rked decrease in motility. Changes in the cooling rate particularly before and during freezing had a notable effect on the sperm motility recovery. Th ere was no or low recovery (0-18%) of sperm motility when the cells were tr ansferred directly to liquid nitrogen from the initial two cooling stages. The data demonstrate the importance of all of the cooling stages in the cry opreservation of the cells. Like glycerol, dimethyl sulfoxide (Me2SO) and e thylene glycol also showed a dose-dependent increase in motility recovery a s well as a biphasic curve of cryoprotection. At optimal concentrations, di methyl sulfoxide (1.00 M) and ethylene glycol (1.29 M) were effective in re covering sperm motility to the extent of 20 and 13%, respectively. Thus the se reagents have markedly lower cryoprotection potential than glycerol. (C) 2000 Academic Press.