Activation of Eggs by Hypothermia in Rats and Hamsters

Previous work on the activation of mammalian eggs by cold has involved treatment of the eggs in vitro, followed by replacement in the Fallopian tube (Chang, 1954), or chilling of the eggs in vivo, by the application of cold water or ice to the tube (Pincus & Shapiro, 1940; Thibault, 1949; Austin & Braden, 1954a, b). In the rat, only the latter method has been employed. As a result of the cold-shock, rat eggs regularly extruded the second polar body and occasionally showed reformation of a nucleus and early cleavage. Since a variety of anaesthetics also induced activation of eggs in rats, it was suggested that the effect was due, in part at least, to the development of a tissue anoxia (Austin & Braden, 1954a). No observations appear to have been reported on the artificial activation of the hamster egg, though some instances of spontaneous activation have been seen (Austin, 1956). The development of methods for inducing profound hypothermia in rats and hamsters provides an opportunity for investigating the activating influence of cold without interference from anaesthesia or surgical operation. The observations described in the present communication show that eggs may be activated at temperatures well within the range that can be tolerated by the animal body as a whole.