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

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Abstract
When freshly ovulated hamster eggs (16 h after human chorionic gonadtropin) were incubated at 37.degree. C in the presence of local anesthetics, the extrusion of the 2nd polar body was inhibited in differing proportions of eggs, depending on the concentration of drug and the age of eggs. Insemination of procaine (3 .times. 10-3 M)- and tetracaine (2 .times. 10-4 M)-treated eggs with capacitated spermatozoa in vitro resulted in .apprx. 80% of eggs showing multiple penetration compared with .apprx. 20% for controls, indicating that local anesthetics 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.degree. 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 initiation of the block to polyspermy in the hamster evidently is dependent on Ca2+-triggered release of cortical granules.