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Toxicological information

Toxicity to reproduction

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Administrative data

fertility, other
based on test type (migrated information)
Type of information:
migrated information: read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Study period:
17 Nov 2003 - 18 Feb 2004
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Valid study design but scope of reproductive endpoints which were examined is limited.
Reason / purpose for cross-reference:
reference to same study

Data source

Reference Type:

Materials and methods

Test guideline
according to guideline
other: Specifications for the Conduct of Studies to Evaluate the Toxic and Carcinogenic Potential of Chemical, Biological, and Physical Agents in Laboratory Animals for the National Toxicology Program (NTP) October 2006
Principles of method if other than guideline:
The guideline "Specifications for the Conduct of Studies to Evaluate the Toxic and Carcinogenic Potential of Chemical, Biological, and Physical Agents in Laboratory Animals for the National Toxicology Program (NTP), October 2006" is similar to the OECD Combined Toxicity/Carcinogenicity Guideline 453 and includes assessment of fertility
GLP compliance:
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Test material form:
other: liquid
Details on test material:
Lot 11108C1, obtained from Aldrich Chemical Company, Milwaukee, WI, USA. Purity > 96% , determined by GC with flame ionization detection. 2.5% water by Karl Fischer titration. Two minor impurities were observed, 0.1 to 1.0% relative to the major peak.

Test animals

Fischer 344
Details on test animals or test system and environmental conditions:
- Source: Taconic Farms, Germantown, NY, USA
- Age at study initiation: 6 weeks
- Housing: Cages and racks were rotated every two weeks during the study. See-Through Systems polycarbonate, solid bottom (Lab Products, Inc., Rochelle Park, NJ), changed twice per week. Heat-treated hardwood chips (P.J. Murphy Forest Products, Montville, NJ), changed twice weekly. Rats were housed 5 per cage
- Diet (e.g. ad libitum): Irradiated NTP-2000 wafer feed (Zeigler Brothers, Inc., Gardners, PA), available ad libitum
- Water (e.g. ad libitum): Tap water via glass water bottles with stainless steel sipper tubes, available ad libitum, changed twice per week.
- Acclimation period: up to 12 days.

- Temperature (°C): 22 +/- 3
- Humidity (%): 50% +/-15%
- Air changes (per hr): 10/hour
- Photoperiod (hrs dark / hrs light): 12 /12

IN-LIFE DATES: From: 17 Nov (males) or 18 Nov (females) 2004. To: 9 Dec (males) or 10 Dec (females) 2004

Administration / exposure

Route of administration:
oral: drinking water
Details on mating procedure:
no mating
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Dosing solutions were prepared by mixing the test material with tap water. The pH was adjusted if necessary with acetic acid to bring it to 6-7.5 pH units. Stability studies of 10 µl/ml formulations were performed periodically by HPLC with ultraviolet light detection and found to be stable (± 10%) under the animal room conditions. They were made and stored in sealed polyethylene bottles. The water was administered to animals in glass bottles with stainless steel sipper tubes and Teflon® seals. Analytical data indicate that little or no volatization occurred under these conditions.
Duration of treatment / exposure:
23 days
Frequency of treatment:
Doses / concentrationsopen allclose all
Doses / Concentrations:
156 mg/L
nominal in water
Doses / Concentrations:
312 mg/L
nominal in water
Doses / Concentrations:
625 mg/L
nominal in water
No. of animals per sex per dose:
Control animals:
yes, concurrent vehicle


Parental animals: Observations and examinations:
Animals were observed twice daily and clinical findings were recorded. Animals were weighed initially, weekly and at the end of studies. Water consumption was recorded weekly by cage.
Oestrous cyclicity (parental animals):
Vaginal samples were collected for up to 12 consecutive days prior to the end of the studies from females of the same dose groups. The vaginal vaults of the females were moistened with saline, if necessary, and samples of vaginal fluid and cells were collected and stained. Relative numbers of leukocytes, nucleated epithelial cells and large squamous epithelial cells were determined and used to ascertain estrus cycle stage (diestrus, proestrus, estrus and metestrus).
Sperm parameters (parental animals):
At the end of the study, spermatid and sperm samples were collected from male rats in the 0, 156, 312 and 625 mg/L dose groups. The following parameters were evaluated: spermatid heads per testis and per gram testis, sperm motility, and sperm per cauda epididymis and per gram cauda epididymis. The left cauda, left epididymis and left testis were weighed. To quantify spermatogenesis, the testicular spermatid head count was determined by removing the tunica albuginea and homogenizing the left testis in PBS containing 10% DMSO). All counts were done with a hemacytometer.
Litter observations:
Postmortem examinations (parental animals):
Complete histopathology was performed on animals of the main 14 week and 2 year studies, which included clitoral gland, mammary gland, ovary, testis (with epididymis and seminal vesicle), thymus, thyroid gland, tongue, trachea, urinary bladder and uterus.
Postmortem examinations (offspring):
For continuous variables, organ and body weight data were analyzed with the parametric multiple comparison procedures of Dunnett (1955) and Williams (1971, 1972). For skewed distribution values (clinical chemistry, etc.), nonparametric multiple comparison methods were used to assess the significance of the dose-related trends.
Reproductive indices:
Offspring viability indices:

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:
no effects observed
Body weight and weight changes:
not specified
Food consumption and compound intake (if feeding study):
not specified
Organ weight findings including organ / body weight ratios:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Chronic progressive nephropathy in males was seen in the high dose group. Hyaline droplet formation was observed, and α2µ-globulin concentration was significantly increased.
Other effects:
not specified

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:
effects observed, treatment-related
Description (incidence and severity):
Estrus cyclicity in the 312 and 625 dose groups may be extended.
Reproductive function: sperm measures:
no effects observed
Reproductive performance:
not examined

Details on results (P0)

There were no clinical findings in any of the dose groups in male or female animals. Renal nephropathy was observed in 625 and 1250 mg/L dose groups in the main study, and hyaline droplet formation associated with α2µ-globulin accumulation was significantly increased. There were no significant differences in sperm parameters of male rats exposed to 156, 312, or 625 mg/L when compared with controls. Exposure-related decreases in testis weight were minimal (< 10%) and accompanied by parallel decreases in terminal body weight. The Markov transition matrix analysis of estrous cyclicity indicated female rats in the 312 and 625 mg/L groups had a signficantly higher probability of extended estrus than the control animals.

Effect levels (P0)

Dose descriptor:
Effect level:
156 mg/L drinking water
Based on:
test mat.
Basis for effect level:
other: The dose of 156 mg/L is equivalent to 22-23 mg/kg bw/d.

Results: F1 generation

General toxicity (F1)

Clinical signs:
not examined
Mortality / viability:
not examined
Body weight and weight changes:
not examined
Sexual maturation:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Histopathological findings:
not examined

Details on results (F1)

Only parental parameters were examined in this study.

Effect levels (F1)

Key result
Remarks on result:
other: no breeding; no F1 generation No adverse effects in reproduction at doses not associated wit h parental toxicity

Target system / organ toxicity (F1)

Key result
Critical effects observed:

Overall reproductive toxicity

Reproductive effects observed:
not specified

Any other information on results incl. tables

3 -Methylpyridine consumption resulted in toxic effects in the kidney. Chronic progressive nephropathy in males was increased in the 625 and 1250 mg/L groups. Hyaline droplet accumulation in the proximal tubules was increased in 1250 mg/L males in the main study. In males ingesting 312, 625 or 1250 mg/L test material, α-globulin concentration was significantly increased in kidney tissue. As alpha-globulin is not synthesized by humans and the proteins in human urine do not exhibit similar protein binding characteristics, this nephropathology is not relevant to human risk assessment (Lehman-McKeeman LD, in Sipes IG, McQueen CA and Gandolfi AJ (eds): Comprehensive Toxicology, Vol 17, Oxford, England:Elsevier, 1997).

3-Methylpyridine has a strong odor (sweetish, described as unpleasant), a low odor threshold (< 1 ppm, AIHA, 1988) and a Henry’s Law Constant (7.73 E-6 at 20oC) which indicates that it volatilizes slightly out of water into the air space above. The substance may be discernible to animals’ olfactory systems, and the animals may avoid drinking water containing the substance. Volatilization in situ in the warm moist nasopharyngeal region of the rat may explain the occurrence of lung toxicity in the main study, when the route of administration is oral. 

3-Methylpyridine is a corrosive substance, and repeated oral dosing of a corrosive substance is a methodological flaw of this study. Chronic administration of a corrosive test material by the oral route may result in local irritation and corrosion effects in test animals, or refusal of the animals to voluntarily consume the test material in the drinking water. Decreased water consumption may lead to dehydration and altered nutritional status of the animals, or result in acute bolus exposure to the test material. Both local irritation and decreased water consumption were documented to have taken place in this study, especially in the first week of exposure.

A category of pyridine and methyl pyridine derivatives is comprised of: pyridine, 2-methylpyridine, 3-methylpyridine and 4-methylpyridine. The basis of the category is structural similarity (based on the pyridine unsaturated ring structure) and similar physical properties, environmental fate and ecotoxicity, and mammalian toxicity. Similar toxicological properties derive from similar physical-chemical properties and common pathways of metabolism and elimination among all members of the category. This category is accepted by the U.S. Environmental Protection Agency (EPA).

Applicant's summary and conclusion

There were no significant adverse findings in male fertility in F344 rats (sperm parameters and testis weights) after 14 weeks of exposure in drinking water to 3-methylpyridine, a category member with pyridine and 2- and 4-methylpyridine. There were no structural effects of this treatment in females, although there was a suggestion of altered estrus cycling at doses of 325 mg/L and higher. This finding may be the result of other complications of the study, and is not highly relevant for human risk assessment. The NOAEL is 156 mg/L, equivalent to 22-23 mg/kg bw/d.