Effects of cryoprotectant treatments on bovine sperm function and osmolyte content

The hypothesis that addition and removal of cryoprotectants to and from spermatozoa would initiate regulatory volume decrease, and lead to osmolyte loss and reduced sperm function, was tested. Common cryoprotectants, in the absence of freezing and thawing, affected bovine ejaculated spermatozoa by lowering their total and progressive motility in medium, reducing their migration through surrogate cervical mucus, damaging sperm head membranes and inducing sperm tail coiling. Sperm function was slightly better maintained after cryoprotectants were added and removed in multiple small steps rather than in a single step. The intracellular content of the polyol osmolytes, D-sorbitol and myo-inositol, exceeded that of the zwitterion osmolytes, L-carnitine and L-glutamate. Certain cryoprotectants reduced intracellular L-carnitine and L-glutamate concentration but not that of myo-inositol or D-sorbitol. Multistep treatments with some cryoprotectants had advantages over one-step treatments in mucus penetration depending on the original amount of intracellular carnitine and glutamate in the spermatozoa. Overall, sperm quality was best maintained by multistep treatment with glycerol and propanediols that were associated with decreased intracellular glutamate concentration. Bovine spermatozoa seem to use glutamate to regulate cryoprotectant-induced cell swelling.