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Toxicological information

Basic toxicokinetics

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Administrative data

Endpoint:
basic toxicokinetics in vivo
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study well documented, meets generally accepted scientific principles, acceptable for assessment.

Data source

Reference
Reference Type:
publication
Title:
Metabolic fate of ethylenethiourea in pregnant rats.
Author:
Kato Y, Odanaka Y, Teramoto S and Matano O.
Year:
1976
Bibliographic source:
Bull. Environ. Contam. Toxicol. 16: 546-555

Materials and methods

Objective of study:
toxicokinetics
Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Metabolic fate of ETU was investigated in the rats administered orally 100 mg/kg of C14-ETU on the 12th day of gestation.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Other name = Ethylenethiourea (ETU)
2-C14-ETU and 4.5-C14-ETU were synthesized from C14-carbon disulfide and 1.2-C14-ethylenediamine dihydrochloride respectively.
Their radiochemical purities were found to be more than 98% by thin layer chromatography in either case.
Radiolabelling:
yes

Test animals

Species:
rat
Strain:
other: Wistar Imamichi
Sex:
female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: no data
- Age at study initiation: no data
- Weight at study initiation: 12-13 weeks
- Fasting period before study: no data
- Housing: individually
- Individual metabolism cages: yes
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum):ad libitum
- Acclimation period:no data

ENVIRONMENTAL CONDITIONS : no data

MATING : Females were mated overnight with adult males. The day when the vaginal plug was found was designed as day 0 of pregnancy.

Administration / exposure

Route of administration:
oral: gavage
Vehicle:
not specified
Details on exposure:
no
Duration and frequency of treatment / exposure:
One administration, on the twelth day of gestation.
Doses / concentrations
Remarks:
Doses / Concentrations:
100 mg/kg of C14-ETU ( 45.87 uCi of 2-C14-ETU or 30.45 uCi of 4.5-C14-ETU).
No. of animals per sex per dose:
no data
Control animals:
not specified
Positive control:
No
Details on study design:
Expired air drawn from the metabolic cage was dehydrated with phosphorous pentoxide and then trapped in monoethanol amine solution.
Animals were anesthetized with ether and the blood sample was taken from vena cana candalis. Then the whole body was perfused with the physiological saline and the following tissues were collected : brain, pypophysis, thyroid gland, thymus gland, lung, liver, adrenal body, kidney, spleen, muscle, bone marrow, placenta, amniotic fluid, and fetus.
Details on dosing and sampling:
Test substance concentrations were measured in maternal blood, in urine and in embryos.
Statistics:
No

Results and discussion

Preliminary studies:
no

Toxicokinetic / pharmacokinetic studies

Details on absorption:
Hydrophilic ETU was so readily absorbed from rat gastrointestinal tract that as early as in 5 min after the dosage significant radioactivity appeared in the blood maternal. The blood level increased rapidly and reached maxiam in 2 hr and then decreased to 0.04 µmole as 2-C14-ETU / g blood by 24 hr.
Details on distribution in tissues:
DISTRIBUTION OF RADIOACTIVITY IN MATERNAL BLOOD.
Radioactivity due to either type of the labeled ETU was found both in the serum and clot. When 4.5-C14-ETU was administered considerable portion of the activity in the serum was related to th serum crude protein fraction, and the percentage grew with the elapse of time. Further washing of the protein fraction with water,ethanol, acetone,and ether could not release any activity indicating the incorporation of 4 and/or 5 carbon atoms of ETU in proteins or other cell constituents. On the other hand in the case of 2-C14-ETU any radioactivity could not be detected in the protein fraction.

RADIOACTIVE SUBSTANCES IN FETUS.
Within 2 hr the radioactivity in the fetus reached maximal and thereafter it was decreased rapidly. The concentrations of radioactive substances estimated as 2-C14-ETU reached 0.220 ± 0.003 µmole/ g in 2 hr and fell clown to 0.012 +/- 0.003 uµole/ g by 24 hr. The fractionation analyses indicated that radioactive carbon of 2-C14-ETU was not incorporated in the fetus protein fractions. About 71 to 73% of the radioactivity in intact fetuses were recovered in ethanol-water fraction(63-69%) and chloroform fraction(3.4-8%). Remaining 27 to 29% of the activity were lost during the fractionation processes. On the other hand,when 4,5-C14-ETU was administered,about three fold of the radioactivities was found in the fetus of 24 hr after the dosage. In this case one third of the activity was due to that incorporated in the protein fraction. And the radioactivities found in the fetuses of 2 and 4 days after the dosage were substantially due to those incorporated in the protein fractions.

RADIOACTIVE SUBSTANCES IN OTHER TISSUES.
Radioactivities due to 2-C14-ETU were distributed comparatively homogeneously in almost all the tissues except the thyroid gland at approximately the saine level as in the serum,and the radioactive concentrations were reduced to about less than 10% of their maximal levels (2 hr). However,in the thyroid gland the radioactive concentration was much higher than the other tissues and increased constantly at least during the first 24 hr indicating the accumulative property of ETU itself or its metabolite(s) in the gland. See table 1.
Transfer into organs
Transfer type:
blood/placenta barrier
Observation:
slight transfer
Details on excretion:
The major elimination route of ETU was the urinary one and 12% of the administered activity (4.5-C14-ETU) were eliminated by 3 hr, and the cumulative percent increased to 80.2 +/- 3.2% by 24 hr and 82.5 +/- 3.1% by two days. In contrast to the ready elimination to the urine, fecal elimination was very low, which was estimated as only 0.53% in two days.
When 4.5-C14-ETU was administered the expiration of radioactive air was detected 15 min after the dosage, then the elimination rate (expired activity per 2 min) increased rapidly followed by the decline through three phases till the end of this experimental term, 192h. No expiration of radioactive gas was observed either from 4.5-C14-ETU itself, radioactive urine, or feces. In contrast to 4.5-C14-ETU, in the case of 2-C14-ETU only a trace level of the expiration was found. These results indicated that the fragmentation of imidazolidine ring ETU and the decarboxylation of 4 and/or 5 carbon atoms of ETU occurred.

Metabolite characterisation studies

Metabolites identified:
yes
Details on metabolites:
As early as in 2 hr considerable quantities of radioactive metabolites were transferred to the foetus, and in addition to ETU, 8 radioactive metabolites were detected.

Any other information on results incl. tables

Table 1 :Distribution of 14C tissues after the single oral dosage of 2-14C-ETU (100 mg/kg, 935 µmole/kg).

14C(µmole as 2-14C-ETU / g tissue)

Tissue

2 hr*

6 hr*

24 hr*

Brain

0.245 ± 0.009

0.195 ± 0.027

0.011±0.002

Lung

0.194 ± 0.019

0.136 ± 0.017

0.009 ± 0.002

Muscle

0.254 ± 0.012

0.207 ± 0.012

0.011±0.004

Liver

0.204 ± 0.026

0.139 ± 0.043

0.021±0.003

Spleen

0.183 ± 0.015

0.142 ± 0.019

0.010±0.002

Kidney

0.243 ± 0.035

0.178 ± 0.019

0.014±0.006

Thyroid gland

0.346 ± 0.100

0.483 ± 0.189

0.651 ± 0.034

Thymus gland

0.165 ± 0.021

0.153±0.013

0.013 ± 0.002

Bone marrow

0.208 ± 0.022

0.155 ± 0.020

0.014±0.001

Adrenal body

0.221 ± 0.054

0.116 ± 0.014

0.016±0.002

Amniotic fluid

0.312 ± 0.086

0.166 ± 0.010

0.012±0.003

Placenta

0.101 ± 0.017

0.054 ± 0.015

0.009±0.002

Serum

0.352 ± 0.017

0.255 ± 0.017

0.022 ± 0.007

Fetus

0.220±0.031

0.163±0.028

0.014 ± 0.002

* Time after the dosage. Values are the means ± S.D. of 4 rats.

Values concerning the fetus are the means± S.D. of 16 fetuses of 4 litters.

Applicant's summary and conclusion

Conclusions:
Interpretation of results (migrated information): low bioaccumulation potential based on study results
The compound was readily absorbed. The concentration reached a maximum in maternal blood within 2 h.  Ethylenethiourea was distributed throughout the maternal system and the embryo. Accumulation was noted in the thyroid. The major elimination route was the urine.
Executive summary:

Metabolic fate of ETU was investigated in the rats administered orally 100 mg/kg of C14-ETU on the twelfth day of gestation. ETU was absorbed readily from the gastrointestinal tract and passed away from the whole body tissues including the fetus rapidly. Only the exception was the thyroid gland and the radioactivity was accumulated in the gland. Most of the administered activity (80.2% 4,5-C14-ETU) was eliminated into the urine in 24 hr and the tissues (including the fetus)levels of radioactivity from 2-C14-ETU reached maximal within 2 hr and fell down to negligible levels by 24 hr. Radiocarbon(s)of 4,5-C14-ETU was expired as radioactivecarbon dioxide and was incorporated into the serum and fetal cellconstituents (crude protein fraction), but that of 2-C14-ETU was neither expired or incorporated into the cell constituents.

From the fetus extract ETU and several radioactive metabolites were detected.