DEFINING BIOASSAY CONDITIONS TO EVALUATE SPERM ZONA INTERACTION - INHIBITION OF ZONA BINDING MEDIATED BY SOLUBILIZED HUMAN ZONA-PELLUCIDA

Objective: Our goal was to study the influence of solubilized human zo nae pellucidae on zona binding potential and acrosome reaction. Materi als and Methods: Zona pellucida (ZP) solutions were prepared by dissol ving zona in acidic buffer NaH2PO4 (pH 2.5), to obtain 0.1 and 0.5 zon a pellucida/mu 1. Zona binding capacity was evaluated by the addition of oocytes (10-fold) to sperm/zona pellucida solution droplets. The nu mber of sperm bound to each oocyte was recorded. Zona pellucida-mediat ed acrosome activity was evaluated after 60 min of coincubation of spe rm and 0.5 ZP/mu 1. Results: The mean (+/-SE) number of sperm bound fo r control, 0.1 ZP/mu 1 and 0.5 ZP/mu 1 was 181.2 +/- 12, 79.6 +/- 5, a nd 38.8 +/- 3, respectively. Zona pellucida-exposed sperm populations showed significant more acrosome-reacted sperm compared to control spe rm, namely, 78 versus 32%, respectively (P = 0.001).Conclusions: The o bserved zona binding inhibition might be ascribed to zona receptor blo cking on the sperm surface or the inability of acrosome-reacted sperm to bind to the zona pellucida.