Acrosome reaction in morphologically different types of human spermatozoa

Background: The aim of our study was to ascertain if the acrosome functionality differs between various morphological types of spermatozoa in human. Methods: Fourteen ejaculates were resuspended in the culture medium with the aim to wash the spermatozoa from the seminal plasma and to induce sperm capacitation. Only motile spermatozoa were isolated from the washed sperm. Each sample was divided into two aliquots. The Ca2+ ionophore was added to the first aliquot to induce sperm acrosome reaction. The second aliquot served as control for evaluating the spontaneous activation of the acrosome. After the treatment, the spermatozoa were fixed in ethanol and their acrosomes were stained with FITC fluorochrome. The samples were observed under an immunofluorescence microscope. The proportion of spermatozoa with functional acrosome (ARIC – acrosome reaction to ionophore challenge) was calculated for each morphological type as a difference between the proportions of spermatozoa with induced and spontaneous acrosome reaction. Results: The mean proportion of spontaneous AR in the analysed sperm samples was 1.6 ± 1.8 %, induced AR 51.8 ± 18.3 % and ARIC 50.1 ± 19.1 %, respectively. Various morphological types of sperm differed significantly from each other by the proportion of successfully induced acrosome reactions (χ2 = 87.62, p < 0.001) and also by the proportion of functional acrosomes (ARIC; χ2 = 101.45, p0.001). All types of morphologically nonoptimal spermatozoa (except the types with round heads and nuclear abnormalities) had a significantly lower percentage of functional acrosomes (p < 0.05) in comparison with morphologically optimal type. Conclusions: The acrosome functionality is related to morphological characteristics of spermatozoa. Optimal morphology types have the highest, while elongated and amorphous types of spermatozoa have the lowest proportion of normal acrosome.