Gebäude 21, 1. OG
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In this study some influences on the weight of 7594 rat fetuses (Bor:Wistar spf; TNO), removed on the 21st day of gestation were examined. Furthermore, he relation between fetal weight and ossification of the fetal skeleton was to e analyzed on a number (n = 1484) of these fetuses.Relation between fetal weight and ossification:The results of this examination lead to a distinction of two categories of skeletal regions.1. The ossification of the metacarpus, the metatarsus and the sternum shows to be extensively complete and independent of the fetal weight.2. A dependency between ossification and fetal weight is found in the proximal, medial and distal phalanges of the fore- and hindlimb as well as in the cervical and coccygeal vertebral column. The strongest correlation between the two variables exists in the phalanges proximales and mediales of the hindlimb. This part of the skeleton may be considered as best indicator of the interdependency between ossification and fetal weight.3. These two categories have to be distinguished for the valuation of embryotoxic effects. Reduced ossification of skeletal regions of the first category must be considered as specific for a substance. Concerning the second category, the association to the reduction of fetal weight has to be taken into account.Influences on fetal weight:The influence of sex, uterine horn, hornsize, intrauterine position and litter size on fetal weight was investigated. The following results were obtained:1. Fetal weight is mainly influenced by litter size. Fetal weight decreases with increasing litter size.2. Fetal weight is influenced by fetal sex. Male fetuses are significantly heavier than female fetuses.3. Fetal weight shows to be independent of hornsize and intrauterine position after the influence of litter size is excluded.4. The position of the fetus in the uterus (right or left horn) has no effect on fetal weight.5. As shown in a biometric analysis, the number of litters to be examined in toxicological studies should be at least 17 for the results of it to be representative and to exclude the influence of litter size on fetal weight.