Toxic Effects of Aromatic Amino Acids on the Livability of Bull Spermatozoa

Abstract

The addition ofL.tyrosine, L.tryptophan, or L.phenylalanine at concentrations as low as 0�5 mM reduced the livability of sperm incubated in Caprogen at 37�C. The toxicity of each amino acid increased with concentration, but L.phenylalanine was most toxic. Catalase (4�5 p.g/ml) significantly increased livabilities but did not completely eliminate the toxic effect of L.phenylalanine or L-tryptophan. The D-amino acids were not toxic. Dialysing egg yolk prior to its incorporation into semen extenders improved sperm livability but the inclusion of catalase produced a significantly greater response. The beneficial effect of catalase was most pronounced at low sperm concentrations (5 million sperm per millilitre). The results suggest that the previously reported dilution effect may be due to peroxide produced from aromatic amino acids.