Results of the Fourteen-Day Studies: In the 14-day studies (dietary rotenone concentrations of 0-600 ppm in the first 14-day studies and 0-4,800 ppm in the second 14-day studies), rough hair coats and dose-related decreases in mean body weight gain were observed in rats. Rats fed diets containing rotenone at concentrations of 1,200 ppm or higher lost weight. No compound-related toxic effects were observed in mice.
Results of the Thirteen-Week Studies: In the 13-week studies (concentrations of 0-1,200 ppm rotenone in feed for rats and 0-50,000 ppm for mice), compound-related effects included lower body weight gain in rats at 150 ppm or more; and bone marrow atrophy and inflammation and hyperplasia of the forestomach in male rats at 300 ppm or more and in female rats at 150 ppm or more. These findings were used to establish the dietary concentrations of rotenone for the 2-year studies.
Experimental Design for the Two-Year Studies: Two-year studies of rotenone were conducted by administering diets containing 0, 38, or 75 ppm rotenone to groups of 50 F344/N rats of each sex for 103 weeks. Groups of 50 B6C3F1 mice of each sex were administered diets containing 0, 600, or 1,200 ppm rotenone on the same schedule. The estimated average amount of rotenone consumed per day was 1.7 mg/kg or 3.5 mg/kg for low dose or high dose rats and 115 mg/kg or 250 mg/kg for low dose and high dose mice.
Survival and Mean Body Weight in the Two-Year Studies: Survival of control and dosed rats was similar (male: control, 22/50; low dose. 31/50; high dose, 30/50; female: control, 27/50; low dose, 32/50; high dose, 31/50). Mean body weights of dosed and control male rats were comparable. Mean body weights of high dose female rats were 5%-9% lower than those of the controls between weeks 58 and 88. Survival of high dose male mice was significantly greater than that of the controls (male: 29/50; 36/50; 47/50; female: 37/50; 42/50; 45/50). Final mean body weights of dosed mice were lower than those of the controls by 8%-13% for males and 17%-24% for females.
Neoplastic Effects in the Two-Year Studies: Parathyroid gland adenomas were observed in 1/41 control, 0/44 low dose, and 4/44 high dose male rats. The historicalincidence of this uncommon tumor in untreated control male rats in NTP studies is 4/1,314 (0.3%). Because these tumors are rare and because the highest incidence ever seen in a control group is 1/50, the increase in these tumors may have been related to rotenone administration.
The incidence of subcutaneous tissue fibromas, fibrosarcomas, sarcomas, myxosarcomas, or neurofibrosarcomas (combined) in low dose female rats was greater (P<0.05) than that in the controls (0/50; 5/50; 3/50). These tumors were combined because of their possible common histiogenic origin from fibroblasts or undifferentiated mesenchymal cells. The incidence of those tumors in the low dose females was greater than the historical rats at this laboratory (9/337, 3% +/- 1%) and throughout the Program (50/2,021, 2% +/- 2%). Because of the lack of a significant dose-related trend and because statistical significance was attained only by combining tumors of differing morphology, the subcutaneous tissue tumors in female rats were not considered to be chemically related. The incidences of these tumors in dosed male rats were not significantly different from that in the controls.
Hepatocellular adenomas or carcinomas (combined) occurred in male mice with a negative (P<0.02) trend, and the incidence in the high dose group was lower than that in the controls (12/47; 12/49; 1/50). Because this low rate of combined liver tumors is unusual, this decrease may have been related to rotenone administration.
Subcutaneous tissue fibromas, sarcomas, fibrosarcomas, or neurofibrosarcomas (combined) in male mice occurred with a significant (P<0.05) negative trend (8/49; 4/50; 2/50). The incidence in the high dose group was significantly lower than that in the controls by the life table test (P=0.01).
Genotoxicity: Rotenone was not mutagenic when tested according to a preincubational protocol with Salmonella typhimurium strains TA100, TA1535, TA1537, and TA98 with or without metabolic activation by rat or hamster liver S9. Rotenone induced forward mutations in the mouse L5178Y/TK+/- lymphoma assay without activation; it was not tested in the presence of S9. Results of tests with rotenone in Chinese hamster ovary cells were negative for induction of sister chromatid exchanges (SCEs) in the absence of exogenous metabolic activation (at concentrations at which the chemical was very toxic), equivocal for SCEs in the presence of rat liver S9 (due to a nonrepeatable positive response when tests were conducted up to toxic concentrations), and negative for chromosomal aberrationsin both the presence and absence of metabolic activation.
Data Audit: An audit of the experimental data was conducted for the 2-year studies of rotenone. No data discrepancies were found that influenced the final interpretations.
Conclusions: Under the conditions of these 2-year feed studies, there was equivocal evidence of carcinogenic activity of rotenone for male F344/N rats, as indicated by an increased incidence of parathyroid gland adenomas (uncommon tumors). There was no evidence of carcinogenic activity in female F344/N rats fed diets containing 38 or 75 ppm rotenone. There was no evidence of carcinogenic activity for male or female B6C3F1 mice fed diets containing 600 or 1,200 ppm rotenone for 2 years. The decreased incidence of liver neoplasms in male mice may have been related to the administration of rotenone.