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

Previous work from our laboratory indicated that gonadotrophin-releasing ho rmone (GnRH) increases human sperm-zona pellucida binding. Here we present evidence that GnRH antagonists inhibit sperm-zona pellucida binding in huma ns. Motile spermatozoa (10(7) cells/ml) were incubated in modified Tyrode's medium at 37 degrees C, in 5% CO2 in air. After 4.5 h, aliquots of spermat ozoa were treated with saline (control) or with different concentrations of GnRH antagonists (test), Each sperm aliquot was then tested in the hemizon a 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 After 20 min, the hemizonae were withdrawn and the numbe r of zona-bound spermatozoa counted using phase-contrast microscopy, In add ition, the effect of GnRH antagonists upon the pattern of sperm movement, f requency of sperm-zona pellucida collisions, and percentage of living and a crosome-reacted spermatozoa was determined. The results indicated that trea tment with GnRH antagonists decreased the number of zona-bound spermatozoa and did not change the pattern of sperm movement, frequency of sperm-zona c ollisions, and percentage of acrosome-reacted spermatozoa, We suggest that this action of GnRH antagonists may be due to an effect on zona receptors o n the sperm plasma membrane.