ZONA-FREE SPERM PENETRATION ASSAY AND INDUCERS OF THE ACROSOME REACTION - A MODEL FOR SPERM MICROINJECTION UNDER THE ZONA-PELLUCIDA

In order to minimize the percentage of false-negative results in the z ona-free sperm penetration assay (SPA), a wide range of substances and /or physical agents capable of inducing the acrosome reaction (AR) hav e been incorporated in the incubation medium. These agents can also be used for treatment of severe male infertility using the technique of sperm microinjection under the zona pellucida (SMUZ). In the present r eview, the percentages of acrosome-reacted spermatozoa induced by seve ral physiological, biochemical or physical agents published in the lit erature are compared in order to find the most efficient method(s) of inducing the AR In human sperm as a previous requirement for optimizin g the technique of SMUZ. A working estimate of the level of efficiency of a given AR inducer is calculated by adding up its range score in e ach of three different arrangements from the highest to the lowest val ue of percentages of AR and differences in percentages of AR and penet ration indexes between treated and control groups in SPA. The agents a ble to induce the AR by nonphysiological (electropermeabilization, lys ophosphatidyl choline, and freezing-thawing) have better positions in this hierarchical system than those ones which require the active part icipation of sperm membrane receptors or second messenger systems (pro gesterone, zona pellucida, and stimulators of protein kinase A). Elect ropermeabilization appears to be the most efficient AR inducer. Howeve r, more possibilities need to be explored to enhance the relatively lo w percentages of acrosome-reacted spermatozoa shown by infertile men.