ABSTRACT
The effect of 8-azaguanine on the development of offspring of mice was investigated by injecting mothers once intraperitoneally with 0·08 to 0·4 mg. / g. of body-weight on a day between the 7th and 15th of gestation.
The principal teratogenic effect was on the skeletal system. Among the malformations found were cleft palates and various abnormalities of the extremities; abnormally directed digits due to deviation of interphalangeal joints were most frequently encountered.
When administered between the 7th and 14th days of gestation, this compound is frequently lethal to embryos, causing death immediately or a few days after injection.
INTRODUCTION
In recent years congenital malformations have been induced in higher mammals by such exogenous factors as nutritional deficiencies, anoxia, certain hormones, and chemicals (Fraser & Fainstat, 1951; Hickey, 1952; Wilson, 1954; Nishimura, 1956). This study was undertaken to ascertain whether 8-azaguanine, an antagonist to guanine, has a teratogenic effect on mouse embryos.
METHOD
Female mice of the Japanese dd strain were mated at 3 to 5 months of age. On days 7 to 15 of pregnancy they were given a single intraperitoneal injection of 8-azaguanine solution (16 mg./c.c.) and then were sacrificed shortly before term to determine state of pregnancy and condition of the foetuses. Routine histological examinations were made of malformed organs and also of the placentae of affected embryos. As controls foetuses from 30 untreated mothers from the same colony were examined.
RESULT
Table 1 shows the results of injection with 8-azaguanine at various times in gestation.
Of 245 control foetuses from untreated mice, only 8 were dead and one malformed (with double ungual process of the first digit of the hind foot). It is clear, therefore, that 8-azaguanine often has a lethal effect. Many embryos seem to have died and become macerated immediately after injection as indicated by the frequency of complete resorptions found at term. Where pregnancy was not interrupted by complete resorption no remarkable alteration in litter size was found.
It is also clear that 8-azaguanine has a considerable teratogenic effect. The malformations occurred mostly in the skeletal system, and especially in the extremities, although there were some cases of cleft palate. Histologically it was observed that the deviated digits, the commonest type of anomaly, were associated with malformed joints and sometimes also with bent proximal bones. In cases of pes varus or pes valgus, luxation of the talocrural joint, hydrops of the tarsal joint with atrophy of the tarsal bone cells or irregularity in form of metatarsal bones was observed. All cleft palates were bilateral; some were incomplete posteriorly, others complete. It should be noted that the critical period for digital anomalies, if one exists, covered a lengthy period, from the 8th to at least the 15th day. No apparent alteration of body-weight was recognized in the living embryos subjected to 8-azaguanine. Placentae of malformed foetuses showed no macroscopic or histological abnormalities.
DISCUSSION
Concerning the mechanism of the teratogenic effect of 8-azaguanine little can be said, except that there was no evidence that the placenta was implicated. The fact that it induced malformations mostly in the skeletal system recalls the results obtained with such agents as nitrogen mustard (Haskin, 1948; Danforth & Center, 1954; Thalhammer & Heller-Szöllösy, 1955; Takagaki, 1957), and ethylurethan (Sinclair, 1950; Nishimura & Kuginuki, 1958). However, 8-azaguanine is peculiar in that it caused numerous slight malformations such as deviation of interphalangeal joints.
ACKNOWLEDGEMENTS
We are grateful to Professor James G. Wilson of the Department of Anatomy of the University of Florida, U.S.A., for his assistance in the preparation of this manuscript.
8-azaguanine was generously supplied by the Tanabe & Co., Osaka.
This investigation was supported in part by a grant in Aid for Fundamental Scientific Research from the Ministry of Education of Japan.
