Chloroethane

Specific investigations: other studies

Administrative data

Endpoint:

endocrine system modulation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

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

Data source

Reference

Reference 1

Reference Type:

publication

Title:

Early changes in sex hormones are not evident in mice exposed to the uterine carcinogens chloroethane or bromoethane

Author:

Bucher, J.R. et al.

Year:

1995

Bibliographic source:

Toxicology and applied pharmacology 130:169-173

Reference 2

Reference Type:

secondary source

Title:

Chloroethane CAS: 75-00-3

Author:

OECD SIDS

Year:

2006

Bibliographic source:

SIDS Initial Assessment Report for SIAM 22

Materials and methods

Principles of method if other than guideline:

The possible relationship of changes in blood concentrations of sex hormones to uterine tumour response was evaluated by examining the oestrous cycle of B6C3F1 mice 21 days prior to and during a 21-day inhalation exposure to 15000 ppm chloroethane, which resulted in the tumorigenic response in the NTP carcinogenicity study. Serum concentrations of estradiol and progesterone were determined at the termination of the exposures and compared to exposure group and stage of the oestrous cycle. Reproductive and endocrine organ toxicity was assessed by histopathological examination.

GLP compliance:

not specified

Type of method:

in vivo

Endpoint addressed:

carcinogenicity

Test material

Test material information

Constituent 1

Reference substance name:

Chloroethane

EC Number:

200-830-5

EC Name:

Chloroethane

Cas Number:

75-00-3

Molecular formula:

C2H5Cl

IUPAC Name:

chloroethane

Details on test material:

- Name of test material (as cited in study report): chloroethane
- Analytical purity: 99.7%

Test animals

Species:

mouse

Strain:

B6C3F1

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratory, Raleigh, NC
- Age at study initiation: 91-97 days
- Housing: 5 per cage (wire caging)
- Diet (e.g. ad libitum): NIH-07 diet
- Acclimation period: 14 days

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: The desired chloroethane exposure concentration was obtained by vapourizing chloroethane in the chamber air supply. The vapours were diluted with conditioned air and delivered to the exposure chambers.
- Method of conditioning air: HEPA filtered, charcoal scrubbed, temperature and humidity controlled.

TEST ATMOSPHERE
- Brief description of analytical method used: actual chamber concentrations were measured every minute by Fourier transform infrared spectrophotometer

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

6h/day

Frequency of treatment:

daily for 21 days

Post exposure period:

Animals were necropsied at the end of the exposure on study day 43.

Doses / concentrations

Dose / conc.:

15 000 ppm (nominal)

Remarks:

corrsponding to 39577 mg/m³

No. of animals per sex per dose:

30 females per group

Control animals:

yes, sham-exposed

Details on study design:

For 21 days prior to the exposures, mice were placed in exposure chambers and sham-exposed for 6 hours/day.
Additional mice were designated as sentinels and housed in the same cage racks and chambers as test animals. Five sentinels were euthanized on arrival and three per chamber at the end of the study. These animals were examined for pathogenic bacteria, murine viruses, mycoplasma and parasites, all with negative results.

Examinations

Examinations:

Body weight:
Time schedule: weekly during the first 21 days and twice during the 3 weeks inhalation

Vaginal cytology:
Time schedule: daily after exposure
The vaginal vaults were lavaged with sterile saline, pH 7.4 and the aspirated lavage fluid and cells were stained with Wright's stain. Relative numbers of leukocytes, nucleated epithelial cells and large squamous epithelial cells were determined and used to ascertain the oestrous cycle stage (i.e. dioestrus, proestrus, oestrus or metoestrus).

Serum estradiol and progesterone concentrations:
After the last exposure on study day 43 mice were anesthetized with 70:30% CO2:O2 and blood was drawn by heart puncture. Serum was collected by centrifugation and frozen at -70 °C for hormone analysis.

Histopathology:
The following organs were examined by light microscopy after staining with haematoxylin and eosin: liver, uterus, pituitary, adrenal glands and ovaries.

Organ weights:
Liver, uterus, ovaries were weighed.

Results and discussion

Details on results:

Clinical signs an body weight:
No exposure-related effects.

Vaginal cytology/Oestrous Cycle Length:
The mean duration of the oestrous cycle was slightly longer in the chloroethane group during exposure than prior to exposure, whereas the oestrous cycle length of controls was unchanged throughout the whole study.
The proportion of time for each of the stages of the cycle differed during exposure to chloroethane when compared to the preexposure period. Mice exposed to chloroethane had a shorter metoestrus and longer dioestrus than during the 21-days prior exposure. However, changes of nearly similiar magnitude were observed in control mice, with a shift of time from metoestrus to oestrus noted during the second 21-day segment compared to the first 21-day period. In conclusion, there were no consistent changes in the oestrous cycle that were clearly related to chloroethane exposure.

Serum oestradiol and progesterone concentrations:
The variance in hormone concentrations was large in both the control group and the group exposed to chloroethane. The inherent variability in the data prevents statistically valid conclusions to be drawn.

Histopathology:
There were no histopathological changes between control and exposed animals with respect to the morphology of the ovaries, pituitary, adrenal glands and uterus.

Organ weights:
There were no significant changes in weights of the liver, uterus or ovary in exposed mice compared to control animals.

Any other information on results incl. tables

Mean oestrous cycle length and proportion of time in phrases of the cycle prior and during exposure to chloroethane

		Mean oestrous cycle length (days)	Relative frequency of oestrous stages (%)
			Proestrus	Oestrus	Metoestrus	Dioestrus
Control [0 ppm]	Prior exposure	5.02 +/- 0.20	17.9	30.8	19.7	31.6
	During exposure^a	5.00 +/- 0.20	16.2	35.4	16.7	31.7
Chloroethane [15000 ppm ]	Prior exposure	5.15 +/- 0.15	17.6	34.1	18.4	29.8
	During exposure^a	5.52 +/- 0.19*	18.3	36.2	12.9	32.5

*: significantly different (p < 0.05) from the mean cycle length prior to exposure

^a: there was significant (p < 0.05) difference in the proportion of time spent in the different oestrous stages during exposure compared to prior to exposure.