EFFECTS OF THE INCORPORATION OF TRITIATED ADENOSINE INTO MOUSE OVARIES ON OVULATION AND DEVELOPMENTAL CAPACITY OF OVA

The sensitivity of mammalian oocytes to irradiation has been recently summarized (Baker, 1971). This report describes the effects of \g=b\-radiationfrom [8-3H]adenosine incorporated into the ovary, on ovulation and on the developmental capacity of ovulated ova. Female ICR mice which were 24 to 26 days old and had been reared in our colony were used in all experiments. Ovaries were exposed to [8-3H]adenosine by injecting 5 \g=m\lof a concentrated solution into the ovarian bursa. The precursor solution contained 12\m=.\5 to 50 \g=m\Ci(Schwarz-Mann, 15 to 25 mCi/ \g=m\mol) in 5 \g=m\lsterile mammalian Ringer's solution buffered at pH 7 with 2 mm-phosphate. Using 25 \g=m\Ciper ovary, the total uptake into the ovary reaches a peak of 7% of the injected precursor in 2 hr, and total incorporation into the nucleic acid fraction of the ovary reaches a peak of 2 % in 1 to 2 days (R. Bachvarova, in preparation). The effect of exposure of the ovary to [8-3H]adenosine on the number of ova released by superovulation is shown in Text-fig. 1. Superovulation was induced by intraperitoneal injection of 7\m=.\5 i.u. PMSG (Gestyl, Organon) followed 48 hr later by an intraperitoneal injection of 7\m=.\5 i.u. HCG (Pregnyl, Organon). Ova were collected and counted from 1 to 26 days after bursal injection of the radioactive precursor, and 90% of the ova were judged to be normal. As can be seen from Text-fig. 1, the yield of ova per female after bursal injection of 50 \g=m\Ci[8-3H]adenosine per ovary increased for ovulations within 1 and 2 days, declined by almost 50% from the initial value within 12 days, remained approximately constant up to 21 days, and declined further after 21 days. The decrease in ovulation was less pronounced when the amount of [8-3H]adenosine injected was reduced. The increased yield of ova at 1 and 2 days after exposure to the tritiated precursor appears to be analogous to the superovulation observed shortly after X-irradiation (Russell 8c Russell, 1956). Since the range of the low energy /?-rays from tritium decay is short (mean range in biological material is 0-6 µ ; Feinendegen, 1967), mostof the radiation received by the oocyte must be due to uptake of the labelled precursor into the oocyte itself. Oocytes may be entirely absent from the ovaries of sexually