Use of the acridine orange staining on smears of human spermatozoa after heat-treatment: evaluation of the chromatin condensation.

A simple, rapid procedure was described to evaluate the degree of chromatin compactness in human spermatozoa. Smears of fixed spermatozoa were heat-treated and stained with acridine orange. Smears from the same sperm samples were also stained with acidic aniline blue. Three groups of semen could be distinguished according to the percentage of red sperm heads observed under fluorescence microscope. 1) Semens with spermatozoa whose chromatin appeared normal before and after heat-treatment. 2) Semens with spermatozoa whose chromatin appeared normal before and abnormal after heat-treatment. 3) Semens with spermatozoa whose chromatin appeared abnormal before and after heat-treatment. The positive correlation between the percentages of red heads and the percentages of blue stained heads suggests that modifications in the biochemical composition of the basic protein component associated with DNA are responsible for the denaturation process.