Induction and Inhibition of the Second Polar Division in the Rat Egg and Subsequent Fertilization

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Abstract
Among 227 eggs from 23 untreated estrous rats, the 1st polar body had persisted in 3 eggs (1.3%) and the 2nd polar division had occurred spontaneously in 2 eggs (0.9%). Emission of the 2nd polar body was induced, in about an hour, by subjecting the rat to anaesthesia with ether, chloroform, ethyl chloride, ethyl alcohol, paraldehyde, nitrous oxide, or intraperitoneal "Nembutal." Ether and nitrous oxide influenced the most eggs. "Nembutal," given subcutaneously, caused no polar body formation. The effect of anaesthetics is probably related to the production of cellular anoxia, and not to the fall in body temperature, for both ether and subcutaneous "Nembutal" depressed the body temperature to the same extent. Cold-shock treatment (ice) led to the formation of the 2nd polar body in virtually all the eggs, and hot-shock treatment (45[degree]C) in none. In untreated rats, the changes undergone by the male and female elements were closely correlated during the early stages of fertilization. A coordinating influence was also evident in the restoration of the normal relationship after it was disturbed by experimental treatment. Shrinkage of the vitellus, involving a reduction of 13% in volume, was found after sperm penetration, and sometimes after cold-shock treatment. Sperms can readily penetrate into eggs that have emitted the 2nd polar body under artificial stimulation; the block to polyspermy is unaffected and seemingly normal fertilization and cleavage may follow. Resumption of the 2nd polar meiosis was inhibited by treatment with hot shock or with colchicine. The influence of hot shock was transient whereas that of colchicine was more lasting. A high incidence of polyspermy (16%) was observed after hot-shock treatment, due evidently to interference with the block to polyspermy. The ways in which the experimental treatments could induce heteroploidy in rat embryos are discussed. The development of the block to polyspermy, the shrinkageof the vitellus, and the emission of the 2nd polar body are independent processes, capable of being evoked separately. Only the block to polyspermy appears to be a specific response to sperm penetration.