Mutagenic effects of cadmium on the oocyte chromosomes of mice.

Abstract

We examined cytogenetically the mutagenic effects of cadmium on the oogenesis (from diakinesis/metaphase I stage to metaphase II stage) of the ddY/F mice in vivo.For the synchronization and stimulation of ovulation, mice were intraperitoneally injected with 5 i.u. of pregnant mare's serum (PMS), and 48 hours later they were also injected with 5 i.u, of human chorionic gonadotropin (HCG). Three hours after the application of HCG, the mice of the experimental groups were given a single subcutaneous injection of 3.0mg or 6.0mg/kg. b. wt. of cadmium chloride. Chromosome analysis was performed on unfertilized metaphase II oocytes recovered from the Fallopian tubes 12 hours after injection of cadmium.The chromosome anomalies observed in the 3mg-and 6mg-cadmium treated groups were numerical ones such as hypohaploidy (n-1), hyperhaploidy (n+1) and diploidy (2n). When analyzed on the litter and oocyte basis, these chromosomal anomalies increased in the cadmium treated groups as compared with the control group. However no structural anomalies of metaphase II chromosomes were observed. As a toxic effect of cadmium, heavier and diffuse haemorrhage was observed on the ovaries in some of the cadmium treated females. Concentrations of cadmium in the ovaries after 12 hours of cadmium injection were 2.5μg/g and 5.0μg/g for 3mg and 6mg treated groups, respectively.The results indicate that cadmium has the potentiality of a mutagen in mammalian meiotic chromosomes. We propose that chromosome analysis of oocytes may be one of the useful methods for the screening of mutagenicity of environmental contaminants in mammalian germ cells in vivo.