Surface properties of the zona pellucida

Structural and sperm binding properties of the hamster zona pellucida (ZP) were investigated using the scanning electron microscope (SEM). The internal and external surfaces of the ZP were found to be morphologically dissimilar. The external surface displayed a fenestrated lattice‐like appearance, whereas the internal surface showed a regular rough appearance. In order to investigate the physiological characteristics of the ZP, zonae were incubated with in vitro capacitated spermatozoa for five minutes and subsequently prepared for SEM examination. Numerous non‐acrosome‐reacted spermatozoa and dissociated acrosomes were observed associated with the external surface of the ZP. Spermatozoa or acrosomes were, however, not observed associated with the internal surface of the zona. Acrosome‐reacted spermatozoa did not adhere to the ZP. It was concluded that the external and internal surfaces of the zona are morphologically and physiologically dissimilar.