Tetrahydro-1,3-dimethyl-1H-pyrimidin-2-one

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

10 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP and guideline study with Klimisch score 1.

Additional information

There are no multigeneration studies available which would assess this property, but substance-induced findings on the male reproductive organs were recorded in a 28 -day subacute oral study at dose levels of 50 and 250 mg/kg bw/d (OECD 407, RCC 1998). Absolute and relative weights of testes and epididymides were distinctly reduced at 250 mg/kg bw/d after the 4-week administration period (e.g. relative testes weights about 52%, relative epididymides weights about 18% below the respective control values) and still statistically significantly below controls after the 2-week recovery period. As a consequence, the testes were reduced in size in all high males (250 mg/kg bw/d) at 4 weeks and after 2 weeks recovery. Histopathologically, there was a moderate degree of seminiferous tubular atrophy in one group 3 (50 mg/kg bw/d) and all group 4 rats. Following the recovery period, severe or massive tubular atrophy was still present in all high dose males, but with some evidence for a possible recovery due to a lower degree of this finding in some testes and some extent of re-epithelialization. Moreover, seminal vesicle atrophy consisting of reduced colloid and atrophic epithelium occurred in one mid dose male (50 mg/kg bw/d) and 3 high dose males (250 mg/kg bw/d) from the main groups. A clear NOAEL for male reproductive organ toxicity was obtained at 10 mg/kg bw/day.

Short description of key information:
NOAEL = 10 mg/kgbw/day (OECD 407; BASF SE/RCC, 1998)
Substance-induced findings on the male reproduction organs were recorded in a 28-day subacute oral study at dose levels of 50 and 250 mg/kg bw/day.

Justification for selection of Effect on fertility via oral route:
No study available. Substance-induced findings on the male reproduction organs were recorded in a 28-day subacute oral study at dose levels of 50 and 250 mg/kg bw/day.

Effects on developmental toxicity

Description of key information

NOAEL (prenatal developmental/maternal toxicity) = 15 mg/kg bw/day (BASF SE, 2000)
NOAEL (teratogenicity) > 60 mg/kg bw/day (BASF SE, 2000)

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP and guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes (incl. QA statement)

Remarks:

testing lab.

Limit test:

no

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

Acclimatization: 10 days minimum prior to pairing with evaluation of health
Age at pairing: 11 weeks minimum
Body weights: 183 - 243 g
Identification: individual animal number tattooed on the pinnae
The animals were housed under standard laboratory conditions: air-conditioning with 10-15 air changes per hour; the environment monitored continuously with hourly recordings of temperature (22 ± 3°C) and relative humidity (40-70%), 12 hours artificial fluorescent light / 12 hours dark with background music played at a centrally defined bw volume for at least 8 hours during the light period.
The animals were housed individually in Makrolon cages with wire mesh tops and standardized granulated softwood bedding.
Pelleted standard Kliba 3433 rat/mouse maintenance diet and tap water in bottles were available ad libitum.

Route of administration:

oral: gavage

Vehicle:

water

Details on exposure:

The mixtures of the test article and vehicle were prepared daily before administration.
The test substance was weighed into a glass beaker on a tared precision balance and die vehicle added (w/v). The mixtures were prepared using a magnetic stirrer. During die daily administration period, homogeneity was maintained using a magnetic stirrer.

Details on mating procedure:

After acclimatization, the females were housed with the males (one male one female) in special automatic mating cages, i.e. with synchronized timing to initiate the nightly mating period, until evidence of copulation was observed. This system reduced the variation in the copulation times of the different females. The females were removed and housed individually if: a) the daily vaginal smear was sperm-positive or b) a copulation plug was observed. This day was designated day 0 post coitum. The male rats used for mating were in the possession of RCC. The fertility of these males was proved and was continuously controlled.

Duration of treatment / exposure:

day 6 - day 20 post coitum

Frequency of treatment:

once daily

Duration of test:

until day 21 post coitum

Remarks:

Doses / Concentrations:
0, 5, 15, and 60 mg/kg bw
Basis:

No. of animals per sex per dose:

25

Control animals:

yes, concurrent vehicle

Details on study design:

The rat is a suitable rodent species for development toxicity studies. The oral route is one possible route of test article exposure. Dose levels were selected, in conjunction with the Sponsor, based on the results of a previous dose range-finding study performed with the test substance.

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
DETAILED CLINICAL OBSERVATIONS: Yes
BODY WEIGHT: Yes
POST-MORTEM EXAMINATIONS: Yes

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes

Fetal examinations:

- External examinations: Yes
- Soft tissue examinations: Yes
- Skeletal examinations: Yes
- Head examinations: Yes

Statistics:

The following statistical methods were used to analyze body weights, food consumption, reproduction and skeletal examination data:
- Means and standard deviation of various data were calculated and included in the report.
- The Dunnett many-one t-test, based on a pooled variance estimate, was used for intergroup comparisons (i.e. single treatment groups against the Control group).
- The Steel test (many-one rank test) was applied when the data could not be assumed to follow a normal distribution.
- Fisher's Exact test for 2x2 tables was applied if the variables could be dichotomized without loss of information.

Details on maternal toxic effects:

Details on maternal toxic effects:
All females survived until scheduled necropsy. No test article-related clinical signs were observed during the course of the study.
Mean food consumption was slightly reduced in the females of the 60 mg/kg body weight group (between 6.5 and 9.4%) when compared with the control group. This reduction is considered to be due to the test article administration.
The body weight, the body weight gain, and the body weight gain corrected for the uterus weight were slightly reduced in the females of the 60 mg/kg body weight group. When compared with the control group mean body weight on day 21 p.c. was 4.3% lower, and body weight gain between days 6 to 21 p.c. was 12.2% lower (86 g gain versus 98 g for control).
The mean gravid uterus weights of the females treated with 60 mg/kg body weight of the test article was slightly reduced. This reduction was considered to be the consequence of the marginally reduced fetal body and placental weights in this group.
No macroscopical changes were observed in any female during necropsy.
There were no differences noted between control and test article treated groups which indicated an embryotoxic effect.

Dose descriptor:

NOAEL

Effect level:

15 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
The sex ratios of fetuses in the vehicle control group and in the dose groups were within the normal range of variation for fetuses of this rat strain.
Mean placental weights, calculated on a litter basis, were slightly lower than for the control in the 15 and 60 mg/kg groups (4.7 and 7.0%, respectively), but statistical significance occurred only at 60 mg/kg. lt is possible that this difference in the 60 mg/kg group was associated with the slight reduction in fetal body weight seen at this dosage.
Mean female fetal body weight, assessed on a litter basis, was slightly reduced (4.3%) in the 60 mg/kg group compared with the control group, and the difference was statistically significant. Mean fetal body weight values (litter basis) for males (4.1%) and overall (4.2%), were also slightly lower than for the control group. There were no statistically significant effect on fetal body weights in the 5 and 15 mg/kg groups.
There were no fetuses with changes considered to warrant classification as a malformation.
No visceral variations were observed for fetuses in any group.
Less common skeletal variations occurred in the fetal skeletons of single fetuses in the 5 and 15 mg/kg groups. One fetus of the 5 mg/kg group and one fetus of the 15 mg/kg had bilateral wavy ribs. No association with the test-article was considered to be indicated. Analysis of other skeletal variations on an individual basis showed isolated statistically significant differences in all groups receiving the test article, caused by lower or higher stages
of development. These findings in the 5, 15 or 60 mg/kg groups were considered incidental as a dose dependency was not evident for the statistical significances when calculation was performed on a litter basis. The examination of the cartilage did not reveal differences between control or test article treated groups.

Dose descriptor:

NOAEL

Effect level:

> 60 mg/kg bw/day

Basis for effect level:

other: teratogenicity

Abnormalities:

not specified

Developmental effects observed:

not specified

Conclusions:

Under die conditions of this study, the oral administration (by gavage) of the test substance to mated female Wistar rats caused only slight adverse effects on the maternal food cansumption and body weight as well as an the placental weights and the fetal body weights at the highest dose level (60 mg/kg). There were no test substance-related influences on other gestational parameters or any signs af teratagenicity up to and including the highest dose level (60 mg/kg).

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

60 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The key study is an GLP Guideline study with Klimisch score 1.

Additional information

Dose range-finding study:

The purpose of this study was to assess the effects of the test article on embryonic and fetal development in mated female rats in order to establish suitable dose levels for the main study on embryo-fetal development in the rat. Each group consisted of 5 mated female Wistar rats. NN'-DIMETHYLPROPYLENE UREA was administered orally by gavage once daily from day 6 through to day 20 post coitum at dose levels of 180, 120 and 60 mg/kg bw/day. The results were as follow:

All females survived up to scheduled necropsy on day 21 post coitum. No test article-related clinical signs were observed during the test period.

Group 4 (180 mg/kg bw/day)

Matemal data

- statistically significant reduction of the food consumption.

- reduction of the body weight, resulting in reduced values about 15.4 %.

- reduction of the mean body weight gain, resulting in reduced values of about 54 % between days 6 and 20 post coitum.

- reduetion of the corrected body weight gains, resulting in reduced values of about 64 %.

Reproduction data

- statistically significant increase of the post implantation loss, resulting in 38.5 % of the implantation sites.

- decreased number of fetuses, resulting in a reduction of about 40 %.

- reduced uterus weight, resulting in reduced values of about 44 %.

Fetal data

- statistically significant reduction of the fetal body weight.

Group 3 (120 mg/kg bw/day)

Matemal data

- reduction of the food consumption.

- reduction of the mean body weight gain, resulting in reduced values of about 35 % between days 6 and 20 post coitum.

- reduction of the corrected body weight gains, resulting in reduced values of about 57 %.

Reproduction data

- statistically significant inerease of the post implantation loss, resulting in 15.5 % of the implantation sites.

- decreased number of fetuses, resulting in a reduetion of about 8 %.

- reduced uterus weight, resulting in reduced values of about 22 %.

Fetal data

- statistically significant reduetion of the fetal body weight.

Group 2 (60 mg/kg bw/day)

Matemal data

- reduction of the food consumption.

- reduction of the mean body weight gain, resulting in reduced values of about 33 % between days 6 and 20 post coitum.

- reduction of the corrected body weight gains, resulting in reduced values of about 58 %.

Reproduction data

- increase of the Post implantation loss, resulting in 11.1 % of the implantation sites.

- decreased number of fetuses, resulting in a reduction of about 12 %.

- reduced uterus weight, resulting in reduced values of about 22 %.

Fetal data

- reduction of the fetal body weight.

Main study:

A prenatal developmental toxicity study of the test item in rats by oral gavage was conducted according to OECD 414 guideline and GLP. NN-DIMETHYLPROPYLENE UREA was administered as an aqueous solution to 25 mated Wistar rats/group by gavage at doses of 5, 15 and 60 mg/kg body weight once daily in the morning from day 6 through to day 20 post coitum (p.c.). A standard dose volume of 10 ml/kg body weight was used. The control group, consisting of 25 mated females, was dosed with the vehicle only (bi-distilled water). All 25 females of the 5 and 15 mg/kg groups were pregnant. 23 females of the 60 mg/kg group and 24 females of the control group were pregnant. All females survived until scheduled necropsy. Na test article-related clinical signs were observed during the course of the study.

In summary, the following findings were obtained and assessed to be test article-related:

Test Group 4 (60 mg/kg body weight/day):

- slight reduction of food consumption (6.5-9.4%), body weight (4.3%) and body weight gain (12.2%), and of placental weights (7.0%) and fetal body weights (4.1-4.3%), when compared with the control group

- no other test article-related effects on gestational parameters or fetuses

Test Group 3 (15 mg/kg body weight/day):

- no test article-related effects on dams, gestational parameters or fetuses

Test Group 2 (5 mg/kg body weight/day):

-no test article-related effects ondams, gestational parameters or fetuses

Overall it was considered that there was no indication of a test article related effect on the incidence of fetal malformations or variations in this study. The rate of skeletal variations, affecting the ribs was lacking in any dose response and a test article-induced origin for these findings can be certainly excluded. Thus, under the conditions of this study, NN'-DIMETHYLPROPYLENE UREA did not affect fetal morphology in the Wistar rat at any of the dose leveis tested.

Taken together,Wistar rats caused only slight adverse effects on the maternal food consumption and body weight as well as on the placental weights and the fetus weights at die highest dose level (60 mg/kg). There were no test article related influences on other gestational parameters or any signs of teratogenicity up to and including die highest dose level (60 mg/kg).

Based on the results of this study, the no observed adverse effect level (NOAEL) for maternal and prenatal developmental toxicity is at least 15 mg/kg body weight per day, while teratogenic effects could not been detected up to 60 mg/kg body weight per day.

Justification for classification or non-classification

Based on a study according to OECD guideline 407 and according to Annex I, Directive 67/548/EEC the following harmonised classification and labelling of the test item is postulated: reproduction toxicity category 3, Xn, R62 "possible risk of impaired fertility".

According to the harmonised classification laid down in Annex I, Regulation No 1272/2008 (CLP), the test item is classified as category 2, and labelled with "Warning" and H361f "suspected of damaging fertility".