Gonadotrophin-releasing hormone antagonists inhibit sperm binding to the human zona pellucida

Previous work from our laboratory indicated that gonadotrophin-releasing hormone (GnRH) increases human sperm-zona pellucida binding. Here we present evidence that GnRH antagonists inhibit sperm-zona pellucida binding in humans. Motile spermatozoa (10(7) cells/ml) were incubated in modified Tyrode's medium at 37 degrees C, in 5% CO(2) in air. After 4.5 h, aliquots of spermatozoa were treated with saline (control) or with different concentrations of GnRH antagonists (test). Each sperm aliquot was then tested in the hemizona binding assay. In this assay, the control aliquot was incubated with half a human zona pellucida (hemizona) and the test aliquot was incubated with the matching half. After 20 min, the hemizonae were withdrawn and the number of zona-bound spermatozoa counted using phase-contrast microscopy. In addition, the effect of GnRH antagonists upon the pattern of sperm movement, frequency of sperm-zona pellucida collisions, and percentage of living and acrosome-reacted spermatozoa was determined. The results indicated that treatment with GnRH antagonists decreased the number of zona-bound spermatozoa and did not change the pattern of sperm movement, frequency of sperm-zona collisions, and percentage of acrosome-reacted spermatozoa. We suggest that this action of GnRH antagonists may be due to an effect on zona receptors on the sperm plasma membrane.