INCREASED ZONA-BINDING ABILITY AFTER INCUBATION OF SPERMATOZOA WITH PROTEINS EXTRACTED FROM SPERMATOZOA OF FERTILE SEMEN

The involvement of proteins extracted from spermatozoa of fertile seme n in sperm-zona binding was examined under hemizona assay conditions. One droplet of a suspension of spermatozoa was exposed to sperm protei ns and then tested for zona binding, while a parallel semen suspension droplet incubated with culture medium served as a control. The reliab ility of the test was increased by relating the number of spermatozoa bound to each inseminated hemizona to the surface area of the hemizona and expressed as the binding index. For spermatozoa incubated with ex tracted proteins, the binding index was greater than (P = 0.001) that of controls (125.2 +/- 45.1 versus 63.6 +/- 29.2, respectively). As a first control, two other protein sources (fetal calf serum and human f ollicular fluid) were tested in the hemizona assay. No significant dif ferences were found in zona binding for other protein-exposed spermato zoa compared with controls. As a second and reverse control, exposure of one hemizona to sperm proteins before insemination with untreated s permatozoa induced a marked decrease (P = 0.0003) in sperm binding, co mpared with that of the matched hemizona not exposed to sperm proteins (control) (3.4 +/- 1.4 versus 74.5 +/- 6.8, respectively). Taken toge ther, these findings confirm the involvement of extracted sperm protei ns in sperm-zona interactions. Therefore, in the cases in which fertil ization in vitro fails because of a lack of sperm-zona binding, incuba tion of deficient spermatozoa with proteins extracted from spermatozoa of fertile ejaculates should restore their ability to interact with t he oocyte and, thus, should enhance the prognosis for in vitro fertili zation.