Triethylenemelamine induced dominant lethals in mice--comparisons of oral versus intraperitoneal injection

Dominant lethal assay of chlordecone and its distribution in the male reproductive tissues of the rat

Male rats received 3.6 or 11.4 mg/kg/day of chlordecone orally for 5 days. Some statistically significant events were seen in the reproductive data of females mated to males receiving chlordecone. However, these events did not follow a consistent pattern and do not suggest the conclusion that chlordecone causes dominant lethal effects. Male rats received a single oral dose (40 mg/kg) of chlordecone and were killed at 1, 2, 3, 5, 7, 14 or 21 days. Chlordecone was distributed throughout the reproductive tract. The descending order of concentration was seminal vesicular fluid greater than prostate greater than vas deferens greater than seminal vesicle greater than unwashed sperm greater than washed sperm. It is concluded that chlordecone is well distributed throughout the reproductive tract of the male rat, appears in the ejaculate, and does not appear to produce dominant lethal effects.

Current status of bioassays in genetic toxicology--the dominant lethal assay. A report of the U.S. Environmental Protection Agency Gene-Tox Program

The term dominant lethal may be defined as death of the heterozygote arising through multiple chromosomal breaks. The assay is generally conducted by treating male animals, usually mice or rats, acutely (1 dose), subacutely (5 doses), or over the entire period of spermatogenesis. Animals treated acutely or subacutely are mated at weekly intervals to females for a sufficient number of weeks to cover the period of spermatogenesis. Those treated for the entire spermatogenic cycle are mated for 1 or 2 successive weeks at the termination of treatment. Females usually are killed at 14 days of pregnancy and examined for the number of total implantations in the uterus, the number of implantations classified as early deaths, and, in some cases, the number of corpora lutea. The category of early death is the most significant index of dominant lethality. A total of 249 papers were reviewed and 140 chemicals were evaluated. Of the 140 chemicals, 65 were positive by the criteria used by the Work Group in evaluating each publication. The category of "positive" includes those responses of a borderline nature. 99 chemicals were declared negative. There is considerable overlap of chemicals in both categories, which accounts for the incongruity in the total number of chemicals tested and the number considered positive and negative. A total of 44 animal carcinogens have been tested in the dominant lethal assay, 26 of which were positive and 18 negative for a correlation of 59%. The role of the assay should be that of confirming positive results from lower tier chromosomal aberration-detecting systems (confirming in the sense of indicating the ability of the chemical to penetrate gonadal tissue and to produce cytogenetic damage). The dominant lethal assay should not be used as a risk assessment method.

Reproductive toxicity and lack of dominant lethal effects of 2,4-dinitrotoluene in the male rat

Adult male Sprague Dawley rats were gavaged with 2,4-dinitrotoluene (2,4-DNT) dissolved in corn oil at 0, 60, 180, or 240 mg/kg/day for five days. A single oral dose (0.5 mg/kg) of triethylenemelamine was used as a positive control. Induction of dominant lethal events was scored on the basis of early fetal deaths. At the two lower doses, no consistent changes were observed in the numbers of pre-implantation losses, implantation sites, or living or non-living fetuses. The highest dose of 2,4-DNT tested resulted in a marked decrease in the numbers of sperm-positive females (determined by microscopic examination of vaginal smears for sperm) and pregnant females. These two effects diminished in the latter weeks of mating. The low number of pregnant females at the highest dose made meaningful statistical evaluations difficult. The results indicate that 2,4-DNT does not cause dominant lethal mutations but does adversely affect reproductive performance.

Dominant lethality in Xenopus laevis induced with triethylenemelamine (TEM)

Adult male South African clawed toads, Xenopus laevis, were injected intraperitoneally with triethylenemelamine (TEM) dissolved in water over a dose range of 13-1,300 micrograms/kg or with water (controls). Mating of the treated males with untreated females was induced seven days later by injection of human chorionic gonadotropic hormone (HCG). Accumulated lethality one week after fertilization among progeny was dose related. Morphological abnormalities among embryos that survived to hatching were similarly dose related. Because anatomically anomalous embryos may have impaired behavior, swimming capacity was tested, and anomalies in swimming behavior were also found to be dose related. Finally, short-term cell cultures were made on minced embryos to obtain chromosome spreads. Structural aberrations, rings, dicentrics, etc of somatic chromosomes were also dose related.

Dominant lethality in frog embryos after paternal treatment with triethylenemelamine: cytogenetics, morphology, and swimming capability

Male frogs (Rana pipiens) were injected intraperitoneally with triethylenemelamine (TEM). The injected males were held for seven days to permit TEM interaction with sperm. The TEM-treated males were then spermiated with human chorionic gonadotropin (HCG) and the ova of normal females were inseminated with the sperm. Direct observation was made of in vitro fertilized ova, cleavage, blastulation, and subsequent embryonic development. No differences were detected between the controls and treated animals from any experimental group for fertilization, cleavage, and blastulation. Dose-related morphologic abnormalities first became apparent at the time of gastrulation; the capability of hatched embryos to swim was affected by TEM. Metaphase chromosomes were studied from randomly selected embryos, and the prevalence of chromosomal structural abnormalities increased with dose over a range of 13--1,300 microgram TEM per kilogram frog.