Prometryn

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Initiation: 22 July 1985; end: 16 August 1985

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1985

Report date:

1985

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

1981

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Prometryn

EC Number:

230-711-3

EC Name:

Prometryn

Cas Number:

7287-19-6

Molecular formula:

C10H19N5S

IUPAC Name:

6-(methylsulfanyl)-N2,N4-di(propan-2-yl)-1,3,5-triazine-2,4-diamine

Test material form:

not specified

Test animals

Species:

rabbit

Strain:

New Zealand White

Details on test animals or test system and environmental conditions:

Source: HARE, Maryland, Hewitt, Ney Jersey, USA
Age: not reported
Weight: 2.97 to 4.01 kg
Acclimation period: 4 weeks
Housing: rabbits were caged individually in mesh bottom stainless steel cages that were changed bi-weekly
Temperature: 18 ± 3 °C
Humidity: 50 ± 20%
Lighting: 14 hours light to 10 hours darkness cycles
Food: Purina Certified Rabbit Chow ad libitum
Water: ad libitum

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

other: Test substance was suspended in 3% cornstarch containing 0.5% Tween 80

Details on exposure:

Substance was administered once daily by oral gavage as 0.04%, 0.24% or 1.44% suspension in the vehicle. A volume of 5 mL/kg bw/day was used. Exposure occurred from day 7 through day 19 of gestation.

Analytical verification of doses or concentrations:

no

Details on mating procedure:

Sexually mature virgin female rabbits were artificially inseminated using semen collected from the buck colony of the same strain maintained at the testing facility.

Duration of treatment / exposure:

Day 7 through day 19 of gestation

Frequency of treatment:

Daily treatment by oral gavage

Duration of test:

29 days

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

2 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

12 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

72 mg/kg bw/day (nominal)

No. of animals per sex per dose:

19 females

Control animals:

yes, concurrent vehicle

Details on study design:

A computer program was used to randomly distribute 76 females into four groups of 19 animals each.

Examinations

Maternal examinations:

The does were observed daily for changes in general appearance and behaviour. Mortality was checked twice daily. Females were weighed on days 0, 7, 10, 14, 20, 24 and 29 of gestation. Feed consumption measurements were taken daily for gestational day 5 through 28. At the time of necropsy, all does were examined for gross pathologic changes. Maternal gross lesions were excised, stored in formalin and eventually evaluated under the microscope.

Ovaries and uterine content:

Not described in report: number of corpora lutea, implantations, viable foetuses, resorptions was recorded for each doe

Blood sampling:

No

Fetal examinations:

At necropsy each foetus was examined viscerally and its sex determined. This examination included the brain, heart, major blood vessels, trachea, lungs, diaphragm, oral cavity, tongue, esophagus, stomach, intestines, liver, gall-bladder, pancreas, thymus, spleen, kidneys, ureters, bladder, adrenals, ovaries and uterus or testicles.
Following the visceral examination the foetuses were placed in 95% ethanol, stained with Alizarin Red S and prepared for skeletal examination. All ossification centres characteristically present at day 29 of gestation in this rabbit strain were checked for presence or absence, size, shape, location and relationship to adjacent ossification centres.

Statistics:

Statistical analysis of the data were performed. Parametric analysis was performed on body weight, weight gain and feed consumption using Bartlett's Test for homogeneity of variance. For homogeneous variances, one-way analysis of variance with Dunnett's method of multiple comparisons was used. Parametric analysis of foetal weight was done using Healy analysis. Non-parametric analysis was performed on the number of corpora lutea, implantations, viable foetuses, resorptions and percentage of post-implantation loss.

Indices:

% post-implantation loss was calculated as follows: [(number of implantation sites - number of viable foetuses)/number of implantation sites] x 100 per doe

Historical control data:

No data provided

Results and discussion

Results: maternal animals

General toxicity (maternal animals)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Few clinical signs were noted for all groups, including alopecia and decreased, soft or no stool. Blood in the pan or vaginal blood was observed in 2 females receiving 12 mg/kg bw/day and 4 females receiving 72 mg/kg bw/day. Other clinical signs were occurring sporadically.

Mortality:

mortality observed, non-treatment-related

Description (incidence):

Three females died during the course of the study, two from the high-dose and one from the mid-dose group. One female died as a result of a dosing accident. Post-mortem examination of a second female revealed the presence of a hair ball in the stomach that was most likely the cause of the death. No explanation could be found for the death of the third animal. Blood was found in the cage pan, and this female may have been aborting. Since no signs of toxicity were observed prior to death, this death was not related to the treatment. An additional three animals were sacrificed during the course of the study due to abortion or early delivery.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Statistically significant reductions in weight gain were detected in the group dosed at 72 mg/kg bw for the test intervals from day 10 to 14 and day 14 to 20 of gestation.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

A statistically significant reduction in the feed consumption was observed in females dosed with 72 mg/kg bw/day.

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Nine females in the study were observed to have abnormal findings at necropsy that were not attributed to treatment. One female in the control group had pitted kidneys. In the group dosed with 12 mg/kg bw/day, one female was observed to have cream coloured amniotic fluid surrounding a foetus, one had a trilobate spleen probably due to an event in early life not related to treatment, and one had a gallbladder that was reduced in size. Two females in the high-dose group were necropsied due to unscheduled death: a hair ball was found in the stomach of one animal, while the second died following a dosing accident. One female presented with a cavitation measuring about 4 mm in diameter in the region of the renal cortex. Another female presented with an enlarged spleen and one with a gallbladder with an irregular, bumpy surface.

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Maternal developmental toxicity

Number of abortions:

no effects observed

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

no effects observed

Early or late resorptions:

effects observed, treatment-related

Description (incidence and severity):

An increase in the mean number of resorptions (early, late and total) and resulting increased post-implantation loss was observed in the group dose at 72 mg/kg bw/day, though it was not statistically significant. This observation was due to females whose pregnancies did not produce viable foetuses.

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

no effects observed

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEL

Effect level:

12 mg/kg bw/day (nominal)

Based on:

test mat.

Basis for effect level:

body weight and weight gain

food consumption and compound intake

Maternal abnormalities

Key result

Abnormalities:

no effects observed

Results (fetuses)

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

no effects observed

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

Two live foetuses were observed to have external malformations. A control foetus had ascites and a foetus from the high-dose group was noted as having a domed cranium. A dead foetus from the high-dose group was found to have a domed cranium filled with green fluid.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

One foetus from the high-dose group was found to have an additional rib and sternebrae. A statistically significant incidence of forepaw proximal phalanges not completely ossified was observed in two low birthweight foetuses from two litters in the high-dose group. This finding was linked to the maternal toxicity observed in this group and thought to represent a slight delay in normal development rather than direct foetotoxicity.

Visceral malformations:

no effects observed

Description (incidence and severity):

Very few visceral malformations were observed (including hydrocephalus, ovarian cyst, misshapened heart, shortened renal papillae, fissures on the dorsal lung surface, elongated median liver lobe, agenesis of the gallbladder) and considered to be spontaneous in nature.

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEL

Effect level:

72 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Fetal abnormalities

Key result

Abnormalities:

no effects observed

Overall developmental toxicity

Key result

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

Despite signs of maternal toxicity, the substance was not embryotoxic, foetotoxic, or teratogenic at doses as high as 72 mg/kg bw/day.

Executive summary:

The potential developmental toxicity of the substance to rabbits was studied under GLP to OECD TG 414. Technical grade material was suspended in 3% corn starch containing 0.5% of Tween 80 and administered by gavage at daily doses of 2, 12, and 72 mg/kg to New Zealand White rabbits (19 animals/group) from days 7 through 19 of gestation. The vehicle not containing test substance was administered to a separate group of 19 pregnant female rabbits serving as the negative control group. Treatment-related effects of maternal toxicity were observed only at the high dose level, including reduction in feed consumption and in maternal body weight gain. In addition, vaginal bleeding was noticed. There were no treatment-related deaths in this study nor any adverse effects on any of the reproductive parameters examined, on foetal body weight, foetal sex ratios or on the incidence of foetal gross, visceral, or skeletal malformations. In two high-dose group foetuses a statistically significant increase in the incidence of a minor skeletal variation was noticed (incompletely ossified forepaw proximal phalanges). This variation was considered to be attributable to the observed maternal toxicity and thought to represent a slight delay in normal development rather than direct foetotoxicity.