Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

Repeated dose toxicity: oral

Administrative data

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

Additional documentation provided in IUCLID assesment reports (Chapter 13) supports the read across approach

Cross-reference

Reason / purpose for cross-reference:

read-across: supporting information

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

Additional documentation provided in IUCLID assesment reports (Chapter 13) supports the read across approach

Reason / purpose for cross-reference:

read-across source

Key result

Dose descriptor:

NOEL

Effect level:

0.065 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Key result

Dose descriptor:

NOEL

Effect level:

0.2 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

0.065 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Conclusions:

16 week oral NOEL (Rat, male): 0.065 mg/kg bw/day
16 week oral NOEL (Rat, female): 0.2 mg/kg bw/day

Executive summary:

The test substance was fed in the diet to primary or recovery rats (10/sex/group). Primary groups were fed the test substance for 16 weeks at dose levels of 0 (control), 0.065, 0.2, or 2 mg/kg bw/day. Recovery groups were fed the test substance at 0 or 2 mg/kg bw/day for 16 weeks and untreated feed for a further 4 weeks.

Parameters evaluated were general health status; body weights and weight gains; hematology (PCV, Hgb, RBC and WBC, platelets, and WBC differential); clinical chemistry (glucose, BUN, creatinine, total protein, albumin, globulin, total bilirubin, ALP, ALT, AST, cholesterol, triglycerides, Na, K, Cl, Ca, and P); urinalysis (primary group only), including microscopic examination of pooled samples/sex/group sediment; final fasted body weight; absolute and relative-to-body-weight organ weights (adrenal glands, brain, heart, kidneys, liver, testes or ovaries, and thymus gland); and gross and histopathologic findings in scheduled tissues and gross lesions from all animals. Histopathologic examination was confined, in primary intermediate and low dose animals, to liver, kidneys, and lungs and, in the recovery animals, to liver, kidneys, lungs, and adrenal glands.

Administration of the test substance resulted primarily in liver changes, more in males than in females, confined almost entirely to animals given the highest dose (2 mg/kg bw/day). Liver involvement was evidenced by very slight/slight hypertrophy and increased eosinophilic staining of centrilobular hepatocytes in males, but not females, fed at 2 mg/kg bw/day; by increased liver weights in both males and females given 2 mg/kg bw/day and in males of the intermediate (0.2 mg/kg bw/day) group; and by increased ALP in males and females fed at 2 mg/kg bw/day. The liver changes appeared to regress quickly. The histopathologic alterations and the increased ALP that occurred after 16 weeks of treatment were not found in the animals allowed to recover for 4 weeks. While relative liver weights were again increased in the recovery group males, the increase over control in the recovery males (5%) vs the primary group males (47%) was comparatively minor.

In addition to the liver effects, the data suggested other, non-target-organ effects of the treatment regimen, particularly at the high dose; however, none of these effects had any immediate adverse consequences for the test animals and would not be expected to result in any long-term consequences for the Involved organ systems. In both primary and recovery group males fed 2 mg/kg bw/day, administration of the test substance was also associated with small decreases in absolute and relative testes weights and small decreases in RBC parameters. No corresponding testicular or bone marrow changes were found histopathologically. In primary group males fed 0.2 and males and females fed 2 mg/kg bw/day, treatment appeared to be additionally associated with decreased cholesterol; increased serum K was found in both sexes treated at 2 mg/kg bw/day. The small cholesterol and potassium differences were not judged to be toxicologically significant.

Under the conditions of this study, the liver was identified as the target organ, and males were more susceptible to the hepatic effects than females. These effects were generally reversible in nature. While the liver weight effects in males at the highest dose were accompanied by histopathologic changes and serum enzyme alterations, at the 0.2 mg/kg bw/day level the only evidence of liver involvement was a slight increase in relative liver weight. The no-observed-effect level (NOEL) for subchronic oral administration of the test substance to rats was 0.065 mg/kg bw/day in males and 0.2 mg/kg bw/day in females.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1989

Report date:

1989

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

The test substance was fed in the diet to primary or recovery rats (10/sex/group). Primary groups were fed for 16 weeks at dose levels of 0 (control), 0.065, 0.2, or 2 mg/kg bw/day. Recovery groups were fed at 0 or 2 mg/kg bw/day for 16 weeks and untreated feed for a further 4 weeks. Parameters evaluated were general health status; body weights and weight gains; hematology; clinical chemistry; urinalysis (primary group only), including microscopic examination of pooled samples/sex/group sediment; final fasted body weight; absolute and relative-to-body-weight organ weights and gross and histopathologic findings in scheduled tissues and gross lesions from all animals.

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

(2R)-2-[4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]oxyphenoxy]propanoic acid

Cas Number:

95977-29-0

Molecular formula:

C15H11ClF3NO4

IUPAC Name:

(2R)-2-[4-[3-chloro-5-(trifluoromethyl)pyridin-2-yl]oxyphenoxy]propanoic acid

Test material form:

liquid

Specific details on test material used for the study:

XRD-535
Lot # AGR-258981
Purity: 99.4%

Test animals

Species:

rat

Strain:

Fischer 344

Details on species / strain selection:

Fischer-344 rats were selected because of their general acceptance and suitability for toxicity testing.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Kingston, NewYork
- Age at study initiation: 6 weeks
- Fasting period before study: No
- Diet: Feed (Purina Certified Rodent Chow #5002) ad libitum
- Water: Muncipal water ad libitum
- Acclimation period: 14 days

Administration / exposure

Route of administration:

oral: feed

Details on route of administration:

The probable routes of human exposure to the test material are via ingestion of foodstuffs that might contain low residues of the test material or from accidental ingestion or dermal contact during manufacture or use. Thus, formulation with feed was the desired method of delivery to assess the potential systemic toxicity of the test material following oral administration.

Vehicle:

other: diet

Details on oral exposure:

DIET PREPARATION
- Rate of preparation of diet: Weekly (based on group mean body weights and feed consumption values so as to maintain the desired dose levels on a mg/kg/day basis)

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Results of analyses for homogeneity in samples taken on Study Day 8 of the female 0.2 mg/kg/day diet were not entirely satisfactory. In view of this, analysis for homogeneity was repeated on samples of both male and female 0.2 mg/kg/day diets mixed the next week (Study Day 15); results of this more extensive analysis showed homogeneous distribution of the test material in the feed, and the Study Day 8 results were judged to reflect sampling variability. Other analyses showed that the test substance was stable in the #5002 feed for at least 7 days, the period of time over which the animals were fed. Samples of premix, control feed, and diets mixed on Study Days 8, 64, 99, and 106 were analyzed to verify target concentrations. With one exception, results were accepted as sufficiently comparable to target concentrations for meaningful interpretation of the data. The concentration check on Study Day 106 showed that test material had been omitted from the diets fed to the female 0.065 and 0.2 mg/kg/day groups for the 16th (final) week of the study. However, analysis of retained samples of the female treated diets prepared the previous week (Study Day 99) allowed the conclusion that this inadvertent deviation from the study plan affected only a small portion of the dosing regimen and did not materially interfere with the study objectives.

Duration of treatment / exposure:

16 weeks

Frequency of treatment:

Daily

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0.065 mg/kg bw/day (nominal)

Remarks:

Primary group

Doses / concentrations 2

Dose / conc.:

0.2 mg/kg bw/day (nominal)

Remarks:

Primary group

Doses / concentrations 3

Dose / conc.:

2 mg/kg bw/day (nominal)

Remarks:

Primary group

Doses / concentrations 4

Dose / conc.:

2 mg/kg bw/day (nominal)

Remarks:

Recovery group

No. of animals per sex per dose:

Primary group (4 groups): 10 per sex per dose
Recovery group (2 groups): 10 per sex per dose

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: On the basis of work with related material, administration of the test material at 2 mg/kg/day for 16 weeks was expected to induce unequivocal hepatotoxicity. It was thought likely that the intermediate dose level of 0.2 mg/kg/day would provide evidence of dose response and the lowest dose level, 0.065 mg/kg/day, would induce no toxicologically significant effects.
- Fasting period before blood sampling for clinical biochemistry: Yes
- Post-exposure recovery period in satellite groups: Yes; two additional groups of 10 rats/sex/group (recovery groups) were fed either 0 or 2 mg/kg/day and then kept for a recovery period of four additional weeks, during which no test material was added to the diet.

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Once daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once weekly

BODY WEIGHT: Yes
- Time schedule for examinations: Weekly once

FOOD CONSUMPTION AND COMPOUND INTAKE :
- Food consumption for each animal determined and mean daily diet consumption calculated: Yes
- Compound intake calculated: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: On receipt of animals

HAEMATOLOGY: Yes
- Time schedule for collection of blood: On Study Days 112-113 (primary males and females) and Study Day 140 (recovery males and females)
- Anaesthetic used for blood collection: Yes
- Animals fasted: Yes
- Parameters checked: Packed cell volume, hemoglobin, red and white blood cells, and platelet counts, complete blood smear examinations (differential WBC counts on 100 cells and an assessment of RBC, WBC, and platelet morphology)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: On Study Days 112-113 (primary males and females) and Study Day 140 (recovery males and females)
- Animals fasted: Yes
- Parameters checked: Alanine transaminase, aspartate transaminase, alkaline phosphatase, bilirubin, calcium, phosphorus, cholesterol, creatinine, glucose, total protein, albumin, triglycerides, urea nitrogen, chloride, potassium, and sodium.

URINALYSIS: Yes
- Time schedule for collection of urine: Study Day 108 from the primary group males and females.
- Parameters checked: pH, protein, occult blood, glucose, ketones, bilirubin, urobilinogen and urine specific gravity

Sacrifice and pathology:

GROSS PATHOLOGY: All animals were necropsied after overnight fasting. Each animal was examined externally and internally for gross pathologic alterations. At the time of the primary and recovery group necropsies, the final fasted body weight of each rat was recorded, and the weights of the adrenal glands, brain, liver, kidneys, heart, thymus, and testes or ovaries were recorded. Organ weights relative to final fasted body weights were afterwards calculated.

HISTOPATHOLOGY: Yes
Representative sections of all the below tissues, including gross lesions, from the primary group high dose and control animals were examined histopathologically.
Adrenal glands, Aorta, Bone, Bone marrow, Brain, Cecum, Cervix, Coagulating gland, Colon, Duodenum, Epididymis, Esophagus, Eyes, Gross lesions, Heart, Harderian/lacrimal gland, Ileum, Jejunum, Kidneys, Larynx, Liver, Lungs, Manmary gland, Mediastinal lymph node, Mediastinal tissue, Mesenteric lymph node, Mesenteric tissue, Nasal tissue, Oral tissues, Ovaries, Oviduct, Pancreas, Parathyroid gland, Peripheral nerves, (sciatic), Pituitary gland, Prostate, Rectum, Salivary gland, Seminal vesicle, Skeletal muscle, Skin, Spinal cord, Spleen, Stomach, Testes, Thymus, Thyroid gland, Tongue, Trachea, Urinary bladder, Uterus, Vagina. In addition, sections of liver, kidneys, and lungs from the primary group intermediate and low dose animals were examined, and, from the recovery group high dose and control animals, gross lesions, lungs, liver, kidneys, and adrenal glands were examined.

Statistics:

Body weights, organ weights, clinical chemistry data, hematology data, and urinary specific gravity data were evaluated by Bartlett's test for equality of variances. Based on the outcome of Bartlett's test, exploratory data analysis was performed by a parametric or nonparametric analysis of variance (ANOVA), followed respectively by Dunnett's test or the Wilcoxon Rank-Sum test with a Bonferroni correction for multiple comparisons. Outliers were identified by a sequential, statistical test, but routinely excluded only from feed consumption data.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Description (incidence and severity):

The daily cageside observations and the weekly clinical observations elicited no positive findings, and the general health status of the animals throughout the study was judged to be unaffected by treatment.

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, non-treatment-related

Description (incidence and severity):

The high dose level females (fed 2 mg/kg bw/day) ate more than controls throughout the study. In these same females, body weight and weight gain values were, for the most part, higher than control values and, in several instances, the differences from control were statistically significant. Body weight gain values of the female low and intermediate dose level groups also tended to be higher than control, but with no concomitant increases in feed consumption. In view of the variability in the data, it could not be concluded that administration of the test material induced increased feed consumption and/or body weight gain.

Food consumption and compound intake (if feeding study):

no effects observed

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

The male high dose (2 mg/kg bw/day) level group showed small decreases in packed cell volume, hemoglobin, and red blood cell count after both 16 weeks of treatment and 4 weeks of recovery. These differences were statistically significant and appear to be associated with administration of the test material. It is doubtful, however, that these differences are toxicologically significant. The differences from control were small (7-8% after 16 weeks and 2-3% after recovery) and, clearly, have no adverse consequences to the rats since they are well within the normal ranges for erythron values for the species.
Refer any other information on results incl. tables

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Alkaline phosphatase activity was statistically significantly increased at the highest dose level (2 mg/kg bw/day) in both sexes after 16 weeks of treatment, more in males than in females. The elevation of this serum enzyme is consistent with the liver toxicity noted at this dose level.
Cholesterol was decreased, relative to control, in the primary group males and females fed at 2 mg/kg bw/day and also in the primary group males given 0.2 mg/kg bw/day.
Potassium was statistically significantly increased in the primary group animals, both males and females, fed at 2 mg/kg bw/day. This difference was also rapidly reversed, with no increase seen again in the high dose level animals allowed to recover for 4 weeks.
Refer any other information on results incl. tables

Urinalysis findings:

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Absolute and relative liver weight means were increased in both sexes fed at 2 mg/kg bw/day. Relative liver weight increases over control also occurred in primary group males fed 0.2 mg/kg bw/day for 16 weeks and in males (only) of the recovery group. The small size of the liver weight increases and the absence of histopathologic liver lesions in the males after 4 weeks on untreated feed were interpreted as signs of recovery.
Absolute and relative weights of the testes were slightly decreased (5-7%) in both the primary and recovery group males fed at the highest dose level (2 mg/kg bw/day). While these minor testicular weight differences appear to be related to the treatment regimen, it is highly unlikely that they would be associated with any adverse reproductive consequences since the histologic appearance of the testes was completely normal.
Refer any other information on results incl. tables

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

No gross lesions attributable to administration were found. The cystic ovarian bursas noted in some recovery group females and the hepatic hernias found in a high dose level group female at 16 weeks and in a high dose level group male at 20 weeks are common, incidental, spontaneous findings in Fischer-344 rats.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Lesions attributable to administration of the test material were found only in the primary group, only in males, and only at the highest dose level (2 mg/kg bw/day). These lesions consisted of an Increase in eosinopnilic staining properties of hepatocytes and a slight Increase in the size of centrilobular hepatocytes.
The hepatic alterations seen in the high dose level males after 16 weeks of treatment were not present in liver sections from recovery group rats of either sex. No histopathologic lesions attributable to treatment were present in the livers of the male rats fed at the low and intermediate dose levels of 0.065 or 0.2 mg/kg bw/day or the female rats fed at any dose level (0.065, 0.2, or 2 mg/kg bw/day).
Incidental lesions, present in liver sections from both male and female primary and recovery group rats, were mononuclear cell foci, microfoci of necrosis often accompanied by inflammatory cells, and bile duct hyperplasia. None of these alterations had a significant impact on the physiologic status of the involved rat liver. Other lesions seen in scattered organs-lacrimal gland mononuclear cell aggregates, suppurative inflammation in the lacrimal gland, colonic nematodiasis, myocardial degeneration, pulmonary alveolar histiocytosis, gastric erosion, and a dermal abscess-were considered to be incidental and spontaneous due primarily to the lack of dose response.

Effect levels

1

Key result

Dose descriptor:

NOEL

Effect level:

0.065 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

organ weights and organ / body weight ratios

2

Key result

Dose descriptor:

NOEL

Effect level:

0.2 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

clinical biochemistry

histopathology: non-neoplastic

organ weights and organ / body weight ratios

Target system / organ toxicity

Key result

Critical effects observed:

yes

Lowest effective dose / conc.:

0.065 mg/kg bw/day (nominal)

System:

hepatobiliary

Organ:

liver

Treatment related:

yes

Any other information on results incl. tables

Table 1: Haematology data (significant observations)

	Dose (mg/kg/day)	PCV (%) (Mean/SD)	Hgb (g/dL) (Mean/SD)	RBC (10E6/mmE3 blood) (Mean/SD)
Primary group males	0	41.3 0.7	15.1 0.1	8.71 0.09
Primary group males	0.065	41.0 0.8	15.0 0.3	8 62 0.17
Primary group males	0.2	41.0 0.5	14.8 0.3	8.55* 0 11
Primary group males	2.0	38.2* 0.8	14.1* 0.2	8.04* 0.17
Recovery group males	0	40.5 0.7	14.8 0.3	8.46 0.18
Recovery group males	2.0	39.6* 1.0	14.3* 0.5	8.21* 0.17
Primary group females	0	40.0 1.0	14.5 0.4	7.75 0.17
Primary group females	0.065	38.9 0.9	14.1 0.3	7.65 0 19
Primary group females	0.2	39.0 1.0	14.1 0.4	7.66 0.20
Primary group females	2.0	40.0 1.1	14.3 0.3	7.77 0 18
Recovery group females	0	39.2 0.9	14.1 0.4	7.58 0.13
Recovery group females	2.0	39.4 1.0	14.4 0.4	7.67 0.17

*Statistically different from control by Dunnett's test, alpha-0.05, two-sided

Table 2: Clinical chemistry (significant observations)

	Dose  (mg/kg/day)	ALP (U/L) (Mean/SD)	Cholesterol (mg/dL) (Mean/SD)	Potassium (meq/L) (Mean/SD)
Primary group males	0	69.4 6.5	61.1 8.0	4.40 0.19
Primary group males	0.065	68.3 7.1	55.6 4.0	4.34 0.17
Primary group males	0.2	64.9 6.0	50.5^$ 2.0	4.53 0.11
Primary group males	2.0	105.1* 14.4	45.8^$ 4.7	4.68* 0.21
Recovery group males	0	75.5 6.7	77.0 29.1	4.32 0.19
Recovery group males	2.0	70.5 6.5	83.0^$ 6.1	4.39 0.17
Primary group females	0	49.9 5 6	109.3 11.8	4.19 0.34
Primary group females	0.065	50.1 6.4	110.8 17.2	4.24 0.23
Primary group females	0.2	45.3 3.7	116.6 11.7	4.31 0.23
Primary group females	2.0	61.5* 10.4	95.6 13.5	4.53* 0.23
Recovery group females	0	42 9 5.1	142.1 11.4	4.07 0.19
Recovery group females	2.0	46.8 6.6	138.6 10.7	4.09 0.22

*Statistically different from control by Dunnett's test, alpha-0.05, two-sided

$Statistically different from control by Wilcoxon's test, alpha-0.05, two-sided

 

Table 3: Organ weights (significant observations)

	Dose  (mg/kg/day)	Absolute liver weight (g) (Mean/SD)	Relative liver weight (g) (Mean/SD)	Absolute testes weight (g) (Mean/SD)	Relative testes weight (g) (Mean/SD)
Primary group males	0	8.508 0.772	2.661 0.122	3.106 0.114	0.974 0.036
Primary group males	0.065	8.436 0.789	2.653 0.092	3.048 0.092	0.964 0.073
Primary group males	0.2	8.708 0.412	2.830* 0.061	3.021 0.057	0.983 0.039
Primary group males	2.0	12.492* 0.642	3.922* 0.132	2.889* 0.106	0.908* 0.044
Recovery group males	0	8.831 0.456	2.600 0.071	3.170 0.106	0.935 0.045
Recovery group males	2.0	9.228 0.476	2.734* 0.099	2.992* 0.100	0.887* 0.028
Primary group females	0	4.846 0.263	2.697 0.132	N/A	N/A
Primary group females	0.065	4.715 0.216	2.684 0.068	N/A	N/A
Primary group females	0.2	4.762 0.190	2.731 0.097	N/A	N/A
Primary group females	2.0	5 453* 0.289	2.998* 0.129	N/A	N/A
Recovery group females	0	4.720 0.267	2.672 0.111	N/A	N/A
Recovery group females	2.0	4.942 0.226	2.751 0.074	N/A	N/A

*Statistically different from control by Dunnett's test, alpha-0.05, two-sided

Applicant's summary and conclusion

Conclusions:

16 week oral NOEL (Rat, male): 0.065 mg/kg bw/day
16 week oral NOEL (Rat, female): 0.2 mg/kg bw/day

Executive summary:

The test substance was fed in the diet to primary or recovery rats (10/sex/group). Primary groups were fed the test substance for 16 weeks at dose levels of 0 (control), 0.065, 0.2, or 2 mg/kg bw/day. Recovery groups were fed the test substance at 0 or 2 mg/kg bw/day for 16 weeks and untreated feed for a further 4 weeks.

Parameters evaluated were general health status; body weights and weight gains; hematology (PCV, Hgb, RBC and WBC, platelets, and WBC differential); clinical chemistry (glucose, BUN, creatinine, total protein, albumin, globulin, total bilirubin, ALP, ALT, AST, cholesterol, triglycerides, Na, K, Cl, Ca, and P); urinalysis (primary group only), including microscopic examination of pooled samples/sex/group sediment; final fasted body weight; absolute and relative-to-body-weight organ weights (adrenal glands, brain, heart, kidneys, liver, testes or ovaries, and thymus gland); and gross and histopathologic findings in scheduled tissues and gross lesions from all animals. Histopathologic examination was confined, in primary intermediate and low dose animals, to liver, kidneys, and lungs and, in the recovery animals, to liver, kidneys, lungs, and adrenal glands.

Administration of the test substance resulted primarily in liver changes, more in males than in females, confined almost entirely to animals given the highest dose (2 mg/kg bw/day). Liver involvement was evidenced by very slight/slight hypertrophy and increased eosinophilic staining of centrilobular hepatocytes in males, but not females, fed at 2 mg/kg bw/day; by increased liver weights in both males and females given 2 mg/kg bw/day and in males of the intermediate (0.2 mg/kg bw/day) group; and by increased ALP in males and females fed at 2 mg/kg bw/day. The liver changes appeared to regress quickly. The histopathologic alterations and the increased ALP that occurred after 16 weeks of treatment were not found in the animals allowed to recover for 4 weeks. While relative liver weights were again increased in the recovery group males, the increase over control in the recovery males (5%) vs the primary group males (47%) was comparatively minor.

In addition to the liver effects, the data suggested other, non-target-organ effects of the treatment regimen, particularly at the high dose; however, none of these effects had any immediate adverse consequences for the test animals and would not be expected to result in any long-term consequences for the Involved organ systems. In both primary and recovery group males fed 2 mg/kg bw/day, administration of the test substance was also associated with small decreases in absolute and relative testes weights and small decreases in RBC parameters. No corresponding testicular or bone marrow changes were found histopathologically. In primary group males fed 0.2 and males and females fed 2 mg/kg bw/day, treatment appeared to be additionally associated with decreased cholesterol; increased serum K was found in both sexes treated at 2 mg/kg bw/day. The small cholesterol and potassium differences were not judged to be toxicologically significant.

Under the conditions of this study, the liver was identified as the target organ, and males were more susceptible to the hepatic effects than females. These effects were generally reversible in nature. While the liver weight effects in males at the highest dose were accompanied by histopathologic changes and serum enzyme alterations, at the 0.2 mg/kg bw/day level the only evidence of liver involvement was a slight increase in relative liver weight. The no-observed-effect level (NOEL) for subchronic oral administration of the test substance to rats was 0.065 mg/kg bw/day in males and 0.2 mg/kg bw/day in females.