In-vitro inhibition of the block to polyspermy of hamster eggs by tertiary amine local anaesthetics.

When freshly ovulated hamster eggs (16 h after hCG) were incubated at 37 degrees C in the presence of local anaesthetics, the extrusion of the second polar body was inhibited in differing proportions of eggs, depending on the concentration of drug and the age of eggs. Insemination of procaine (3 X 10(-3) M)- and tetracaine (2 X 10(-4) M)-treated eggs with capacitated spermatozoa in vitro resulted in approximately 80% of eggs showing multiple penetration compared with approximately 20% for controls, indicating that local anaesthetics interfere with the block to polyspermy in the egg. This effect was reversed by raising the concentration of Ca2+, but not Mg2+, during treatment with the drug or washing the drug-loaded eggs in Ca2+-containing medium. When the treatment of eggs was carried out at 4 degrees C, no such inhibition of the block to polyspermy was observed. The extrusion of cortical granules was delayed by procaine, although the rate of fertilization was not affected. The results provide evidence to support the belief that the initiation of the block to polyspermy in the hamster is dependent on Ca2+-triggered release of cortical granules.