Retention of biologic characteristics of zona pellucida in highly concentrated salt solution: The use of salt-stored eggs for assessing the fertilizing capacity of spermatozoa

When unfertilized hamster eggs are placed in highly concentrated solutions of neutral salts (e.g., 2 M ammonium sulfate), the egg proper, or vitellus, shrinks, creating a large perivitelline space; the zona pellucida remains unchanged in appearance under the light microscope. When these eggs are inseminated, many spermatozoa attach to and penetrate the zona. The specificity as well as several physical and chemical characteristics of the zona seem to remain unchanged during storage of the eggs in salt solutions. The properties of the human zona pellucida which allow the attachment and penetration of human spermatozoa are also retained in concentrated salt solutions. Shipment of salt-stored human eggs at ambient temperature to any part of the world is feasible and inexpensive. The present study suggests that salt-stored eggs can be used as substitutes for fresh living eggs in the preliminary assessment of fertilizing capacity of spermatozoa when collection of a large numer of fresh unfertilized eggs, particularly in humans, is not practical.