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ANITA M. MANDL

Summary.

Direct irradiation of one ovary with 315 or 630 r was followed by a reduction in the number of eggs shed on the irradiated side, and compensatory overactivity by the unirradiated ovary. Unilateral irradiation with 157 r, or exposure of one ovary to air (involving surgical handling) induced slight superovulation on the treated side. The total number of eggs shed by both ovaries was highest in unilaterally irradiated animals whose second ovary was exposed to air; slightly fewer eggs were shed by those whose second ovary was left untouched; and the least number was recorded for control animals one of whose ovaries was exposed to air (the other left untouched). The degree of superovulation was less pronounced than that recorded for rats irradiated bilaterally with 157 r (cf. Mandl, 1963a). The results suggest that the superovulatory effect of irradiation is primarily due to `non-specific' damage to the ovary, and is mediated by a reduction in the number of pre-existing large Graafian follicles undergoing atresia.

Newly-formed corpora lutea in unilaterally irradiated ovaries were consistently smaller than those in non-irradiated ovaries. The effect is apparently due to radiation-induced damage sustained by the granulosa cells before ovulation.

In animals irradiated at metoestrus and which mated the following oestrus, the number of unfertilized eggs was higher on the irradiated than on the unirradiated side. Even so, the proportion of unfertilized eggs on the unirradiated side was higher than in normal animals.

The proportion of tubal eggs showing morphological abnormalities was very low. By the time of autopsy, 9 to 10 hr after expected ovulation, pronuclear development had not proceeded as far in unilaterally irradiated as in unirradiated animals. The effect was particularly marked on the unirradiated side. Unilateralirradiation appears to disturb the developmental synchronization of oocytes between the two ovaries, and may induce the premature rupture of a small number of follicles.