In vitro induction of the acrosome reaction in ovine spermatozoa by calcium ionophore A23187

The relationship between concentration of calcium ionophore A23187 and incubation time upon the proportion of spermatozoa undergoing acrosome reaction (AR) in vitro was investigated in rams from a commercial artificial insemination (AI) program. Two ejaculates were collected by artificial vagina from each of nine rams of three breeds (Finn Dorset, Charolais and Suffolk) aged 8-36 months. Each ejaculate was diluted in a skimmed milk extender. Spermatozoa were thereafter incubated for 45 or 60 min in modified Tyrode's medium (TALP) which contained either zero, 0.1 or 1.0 microM/l A23187. After fixing in 10% formaldehyde, the number of spermatozoa that had undergone AR was determined by phase contrast microscopy. In pre-incubation samples, 21.3 +/- 3.3% of spermatozoa had undergone AR. Percentages of acrosome reacted spermatozoa were significantly (P < 0.001) increased after incubation with A23187. After incubation with 0.1 microM/l A23187 for 45 and 60 min there were 22.4 +/- 3.0% and 31.7 +/- 4.3% acrosome reacted spermatozoa, respectively. After incubation with 1.0 microM/l A23187 for 45 and 60 min there were 46.2 +/- 6.5% and 53.8 +/- 5.9% acrosome reacted spermatozoa, whilst corresponding numbers in control samples were 17.0 +/- 2.7% and 22.3 +/- 4.2%. There was also a significant (P < 0.001) effect of individual animals upon the responses to different concentrations of A23187. These findings indicate that (i) A23187 can be used to assess the AR of ovine spermatozoa in vitro and (ii) there are effects of individual animals upon the proportion of spermatozoa undergoing AR.