Methyloxirane

Neurotoxicity

Administrative data

Endpoint:

neurotoxicity: sub-chronic inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1983-04-04 till 1985-10-23

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP near guidline study, acceptable for assessment.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1985

Report date:

1985

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 424 (Neurotoxicity Study in Rodents)

Principles of method if other than guideline:

test animals: 30 male Fisher Rats of a 2-generation study of PO were exposed to 0, 30, 100 or 300 ppm PO.
6 h/day, 5 d/week. Total exposure 24 weeks.
On all male rats from all groups an obeservational battery was conducted on 8, 16 and 24 weeks. And prior to necropsy the rats were subjected to an open field activity test and a hind limb grip strength test. 10 rats of every group were given a thorough neurohistologic examination.

GLP compliance:

yes

Remarks:

Mammalian and Environmental Toxicology Research Laboratory Health and Environmental Sciences, Dow Chemical, USA. Midland, Michigan 48640

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Methyloxirane

EC Number:

200-879-2

EC Name:

Methyloxirane

Cas Number:

75-56-9

Molecular formula:

C3H6O

IUPAC Name:

2-methyloxirane

Details on test material:

Propylene oxide: lot nr 30215 III, was supplied by ARCO
composition analysis was performed by gaschromatography and electron impact gas chromatography-mass spectometry.
purity: >99.9 %

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratory, Kingston NY
- Age at study initiation: P 7 weeks
- Weight at study initiation: no data
- Fasting period before study: no data
- Housing: individually
- Diet :ad libitum
- Water :ad libitum
- Acclimation period: 2 weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22
- Humidity (%): 40 - 60
- Air changes (per hr): 6 h/day exposure to test material
- Photoperiod (hrs dark / hrs light): 12 hour photocycle

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION

Exposures were conducted in 14.5 cubic meter chambers with stainless steel pyramidal shaped ceilings and epoxy resin coated floors and walls.
All chambers were operated under dyhamic airflow conditions at a slight negative pressure relative to the surrounding area. Control animals were
placed in an identical chamber. Air supplied to the chambers was controlled by a system designed to control temperature (approximately 22'C)
and relative humidity (approximately 50%). These data were recorded each exposure day.

Propylene oxide test atmospheres were generated by vaporizing the liquid at controlled rates using glass J-tubes (Miller et al., 1980).
The vapors were swept from the J-tubes with compressed air into the air inlet ducts of the chambers where there was further dilution to the
desired concentration. The compressed air was preheated wlth a flameless heat torch (Master, Model FHT-4) at approximately 34 degrees C, in order
to facilitate complete vaporization of the liquid test material. Total chamber airflow was maintained at approximately 2200 liters per minute.

The concentration of the test material in each chamber was determined at least once per hour by a MIRAN I infrared spectrophotometer at a
wavelength of 11.95 microns. The nominal concentration (ratio of the amount of test material to the total anount of air through the chamber)
was calculated for each chamber on a daily basis.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

once an hour by MIRAN 1 infrared spectrophotometer at a wavelength of 11.95 microns. The nominal concentration was calculated for each chamberon a daily basis.

Duration of treatment / exposure:

6 hours/ day for 24 weeks

Frequency of treatment:

first 14 weeks: 5 days a week
from week 15: 7 days a week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0, 30 , 100 and 300 ppm
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
0, 70, 240 and 710 mg/m3
Basis:
analytical conc.

No. of animals per sex per dose:

30

Control animals:

yes

Details on study design:

An observational battery was conducted on all male rats from each dose level after approximately 8, 16, and 24 weeks of exposure.
Just prior to necropsy all surviving male rats were subjected to an open-field activity test and a hind limb grip strength test. A subset of l0 male
rats/exposure level were then perfusion-fixed and given a thorough neurohistologic examination.

Examinations

Observations and clinical examinations performed and frequency:

Each animal on study was observed for signs of toxicity and changes in demeanor at least once a day.
Rats dying spontaneously or found moribund were submitted for pathologic examination.

All male rats were weighed weekly throughout the study.

Specific biochemical examinations:

NEUROPATHY TARGET ESTERASE (NTE) ACTIVITY: Yes / No / No data
- Time schedule for examinations:
- How many animals:
- Method of sample collection and processing:
- Tissues used:
- Animals fasted: Yes / No / No data
- Description of methodology for NTE determination:
- Other:


CHOLINESTERASE ACTIVITY: Yes / No / No data
- Time schedule for examinations:
- How many animals:
- Method of sample collection and processing:
- Tissues used:
- Animals fasted: Yes / No / No data
- Description of methodology for NTE determination:
- Other:


OTHER:

Neurobehavioural examinations performed and frequency:

Observational Battery:
The observational battery was performed 3 times during the exposure phase of the study at approximately 8-week intervals. The third repetition
was within 1 week of sacrifice. The test was performed on all surviving male rats in the control and each of the 3 exposure groups.
Exposure to the test material was discontinued for at least 12 hours prior to testing.

Parameters examnined:
Evasive Behavior
Muscle Tone
Tremor
Haircoat Condition
Salivation
Lacrimation
Urine Staining
Fecal Staining
Locomotor Behavior (gait, pattern, intensity)
Responsiveness to touch
Responsi veness to sharp noise
Responsiveness to tail pinch
Visual Placing

Open Field Test.
The open field test was performed once on each surviving rat in the control and 3 exposure groups at the end of the exposure phase of the
study. Exposure to the test material was discontinued for at least 24 hours prior to testing.

Hind Limb Grip Strength.
Hind limb grip strength was detremined for each surviving rat in the control and 3 exposure groups at the end of the exposure phase of the study.

Sacrifice and (histo)pathology:

A subset of 10 randomly selected male rats from the control and each of the exposure groups was selected for the neuropathologic examination.
The day following evaluation in the open field test and grip strength test, these rats were submitted for whole body perfusion and necropsy
examination. All rats were injected intraperitoneally with 0.2 ml/100 gm body weight {of a heparin solution (10,000 USP units/mt) approximately
10-15 minutes before anesthesia with methoxyflurane. The heart was then surgically exposed and a 19-gauge butterfly cannula was inserted into
the left ventricle. Following a brief perfusion with a 1% sodium nitrite (vasodilator) solution, the carcass was perfused with a glutaraldehyde (1.5%)
formalin (4%) solution until optimum fixationwas achieved.

After perfusion the rats were examined for gross lesions and the following tissues were retained in 10% neutral buffered formalin: brain, spinal cord, sciatic nerves, tibial nerves, digital nerves (retained both hind feet), eyes, and nasal cavity/turbinates.
Histopathotogic examination of the retained tissues was limited to the control and highest exposure concentration rats (300 ppm).

Results and discussion

Effect levels

Dose descriptor:

NOAEC

Effect level:

300 ppm

Sex:

male

Basis for effect level:

other: only decreased weight gain in rats exposed to 100 and 300 ppm propylene oxide. No evidence of neurotoxicity

Remarks on result:

other:

Any other information on results incl. tables

none