Rats, liver/thyroid tumors

Case Study 2 An evaluation of the human relevance of the liver and thyroid tumors in rats induced by pyrethrins based on mode of action [118, 128-130]... 

A recent study confirmed that ethylene thiourea was carcinogenic in male and female rats as shown by increased incidences of thyroid follicular cell neoplasms after treatment of up to 250 ppm in the diet for 2 years. In mice, concentrations ranging from 100 to 1000 ppm for 2 years caused liver and pituitary tumors in addition to thyroid tumors. Perinatal exposure up to 8 weeks followed by a control diet for 2 years was not carcinogenic in rats or mice. Combined perinatal-adult ETU exposures produced the same carcinogenic effects as adult-only exposures. 

Mirex 2B e B2 Mouse, rat liver tumors and thyroid tumors... 

Ethylenethiourea, which produces thyroid carcinomas in rats and liver cell tumors in mice by ingestion, is formed from ethylenebisdithiocarbamates such as Maneb and Zineb by metabolic processes and cooking. 

Carcinogenic response was observed after exposure to nitrobenzene in rats and mice mammary adenocarcinomas were observed in female B6C3Ei mice, liver carcinomas in male Fischer-344 rats and thyroid follicular cell adenocarcinomas in male Fischer-344 rats. Benign tumors were observed in five organs. 

Pyrethrum has been used for many years as an insecticide for household, agricultural, and other applications. Pyrethrins exhibit a low order of toxicity in mammals and are rapidly metabolized. However, the chronic administration of pyrethrins to rats has been shown to result in liver and thyroid gland tumor formation [128,129]. The carcinogenicity of pyrethrins has been examined in both the mouse and rat. 

D5 has slightly different properties than D4, and it does not have any estrogenic activity [289]. It does, however, also have adverse effects on the reproductive system, much like D4, but also on the adipose tissue, bile production, and even immune system due to D5 s effect of reducing the prolactin levels [291]. In addition, it was determined that D5 causes a significant increase in uterine tumors in rats after a 160 ppm exposure. However, it is proposed that the tumors occur in rats through a mechanism that would not affect humans [291]. D5 also acts as a dopamine agonist and it can cause adverse effects on the nervous system in humans [291]. For exposures to D6 in rats, an increase in liver and thyroid mass and reproductive effects were observed [292]. 

Neoplastic effects in the NTP (1986) bioassay included increased incidences of neoplastic nodules in the liver in the male and female rats and hepatocellular adenoma or carcinoma (combined) in the male mice. Slightly elevated incidences of thyroid gland follicular cell tumors were additionally observed in exposed male mice, although the increases were equivocal. No exposure-related neoplastic changes were found in the chronic study of the 77.4% decaBDE mixture (Kociba et al. 1975 Norris et al. 1975a), but the power of this study to detect carcinogenic effects is limited by the very low dose levels in comparison to those tested in the NTP bioassay. 

The thiomethyl- and mcthoxy-v-triazines, as well as the asymmetrical triazine metribuzin, were not carcinogenic -some even in the SD rat - and at feeding levels exceeding the MTD the exception was terbutryn, where an increased incidence of mammary, thyroid, and liver tumors were observed in female SD rats at feeding levels that exceeded the MTD. 

Exposure to 0.05-0.5 ppm 1,1-dimethylhydrazine for 6 months produced an increased incidence of leukemia and tumors of the pancreas, pituitary, blood vessels, liver, and thyroid in mice and/or rats (Haun et al. 1984). Tumors of the lung, liver, nasal cavity, bone, and blood vessels were observed in mice exposed to 5 ppm 1,1-dimethylhydrazine for 1 year (Haun et al. 1984). A significantly increased incidence (p 0.05) of nasal tumors and thyroid carcinomas was observed in male rats exposed intermittently to 1 and 5 ppm hydrazine, respectively, for 1 year (Vemot et al. 1985). Hamsters and rats exposed to 750 ppm hydrazine once for 1 hour, or 1 hour per week for 10 weeks, exhibited increased incidences of squamous metaplasia, hyperplasia, and neoplasia in the nose (Latendresse et al. 1995). Nasal tumors were also noted in hamsters and female rats intermittently exposed to 5 ppm hydrazine for 1 year (Vemot et al. 1985). Tumor incidence was not significantly increased in mice and dogs exposed intermittently to 1 ppm hydrazine for 1 year (Vemot et al. 1985). The studies suggest that hydrazine and... 

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