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Repeated dose toxicity: oral

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Administrative data

Endpoint:
short-term repeated dose toxicity: oral
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
Cross-reference
Reason / purpose:
read-across: supporting information

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1981

Materials and methods

Test guideline
Qualifier:
no guideline available
Principles of method if other than guideline:
30 male Wistar rats were feeded with the test substance in olive oil for 8 weeks. The conduction velocity of the peripheral nerve was obtained in the rats tail.
Therefore the rat kept immobilized by wrapping into a towel, turned on his back and got electrodes inserted in his tail. Then the tail was immersed in a warm parrafin bath and the tail nerve was stimulated by a square pulse of 0.2 ms and supramaximal strenght. Biopotentials were observed with an adscope between two different distances.Then the conduction velocity was calculated.
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Test material form:
liquid
Specific details on test material used for the study:
The four chemicals (2-methylpentane, 3-methylpentane, methylcyclopentane and n-hexane) used were more than 99 % pure.

Test animals

Species:
rat
Strain:
Wistar
Sex:
male
Details on test animals and environmental conditions:
thirty Wistar male rats: mean body weight 343 g, SD 27 g

Administration / exposure

Route of administration:
oral: unspecified
Vehicle:
olive oil
Details on oral exposure:
The solvents were diluted with olive oil and orally administered for 8 weeks. Weeks 1-4: 0.4 ml test substance + 0.6 ml olive oil, weeks 5-6: 0.6 ml test substance + 0.4 ml olive oil, weeks 7-8: 1.2 ml test substance + 0.8 ml olive oil
Duration of treatment / exposure:
8 weeks
Frequency of treatment:
once daily
Doses / concentrationsopen allclose all
Dose / conc.:
0.4 other: ml
Remarks:
wks. 1-4
Dose / conc.:
0.6 other: ml
Remarks:
wks. 5+6
Dose / conc.:
0.8 other: ml
Remarks:
wks. 7+8
No. of animals per sex per dose:
5-7 (males only)
Control animals:
yes, concurrent vehicle
Positive control:
5 different test substances tested

Examinations

Observations and examinations performed and frequency:
before administration and after 2, 4, 6 and 8 weeks; Body weight, conduction velocity, motor distal latency, mixed nerve conduction velocity
3 points at the rat´s tail were inserted with electrodes: A (3 cm down from the anus), B (7-10 cm down from A) and C (3-4 cm up from the tail`s end). Stimulating at A or B by a single stimulation and measuring the resulting EMGs at C were used to obtain the motor nerve conduction velocity (MCV) and the distal latency (DL). Stimulating the nerve at C by 100 times by 2 c/s and measuring the nerve impulses at A and B obtained the mixed nerve conduction velocity (MNCV).

Results and discussion

Results of examinations

Clinical signs:
not examined
Mortality:
not examined
Body weight and weight changes:
no effects observed
Description (incidence and severity):
The changes in body weight are shown in Fig. 2. There were no statistically significant differences between the solvent-administered groups and the control.
Food consumption and compound intake (if feeding study):
not examined
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
no effects observed
Description (incidence and severity):
No abnormal changes in the behavior of rats were found in every group throughout the experiment.
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
not examined
Gross pathological findings:
not examined
Neuropathological findings:
effects observed, treatment-related
Description (incidence and severity):
The changes in MCV are shown in Fig. 3 MCV in the n-hexane group was significantly less than the control after four and eight weeks of administration. MCV in methylcyclopentane group was significantly less than the control after eight weeks' administration. But there was no significant difference between MCVs in 2-methylpentane or 3-methylpentane group and the control.
DLs in every groups had a tendency to decrease as the rats grew. There were no statistically significant differences between the solvent-administered groups and the control.
Histopathological findings: non-neoplastic:
not examined
Histopathological findings: neoplastic:
not examined

Any other information on results incl. tables

The changes in MNCV (distal) are shown in Fig. 4. MNCV (distal) in n-hexane group was significantly less than the control after four weeks' administration. But there was no significant difference between MNCVs (distal) in 2-methylpentane, 3-methylpentane or methylcyclopentane group and the control.

The changes in MNCV (proximal) are shown in Fig. 5. MNCV (proximal) in n-hexane group was significantly less than the control after six weeks' administration. MNCVs (proximal) in the 2-methylpentane and methylcyclopentane groups

were significantly less than the control after eight weeks' administration.

The summary of the results is shown in Fig. 6. The results demonstrated that the n-hexane group showed a distinct impairment of the functional states of the peripheral nerve, the methylcyclopentane and 2-methylpentane groups showed

only slight impairment of them, and 3-methylpentane group barely showed any impairment.

The ratios of the conduction velocities and distal latencies to the predosing ones were calculated and compared between each solvent-administered group and the control group (Fig. 7). MNCV (distal) significantly differed from that of the

control even in 3-methylpentane group after eight weeks' administration. There were no significant differences in distal latency.

Applicant's summary and conclusion

Conclusions:
The n-hexane group showed a distinct impairment of the functional states of the peripheral nerve Methylcyclopentane, 2-methylpentane and 3-methylpentane group had some significant differences in comparison with the control in the experiment, although these differences were not so distinct as those in n-hexane group. The results revealed that the neurotoxicity of the three chemicals was not so severe as that of n-hexane and were in the order of
n-hexane > methylcyclopentane > 2-methylpentane = 3-methylpentane.
Executive summary:

Commercial hexane which caused polyneuropathy in many workers contained 10-40 % of 2-methylpentane, 3-methylpentane and methylcyclopentane in addition to n-hexane. The hexacarbon compounds methyl n-butyl ketone, 2,5-hexanedione and etc were shown to be neurotoxic like n-hexane. Therefore, 2-methylpentane, 3-methylpentane and methylcyclopentane which are also hexacarbon compounds were suspected to be neurotoxic, but their neurotoxicity had not been sufficiently investigated.

The present experiment was performed to clarify their neurotoxicity by measuring the nerve conduction velocity in the rat's tail Thirty rats were divided into five groups of 5-7 rats. n-Hexane, 2 -methylpentane, 3-methylpentane and methylcyclopentane were diluted with olive oil and orally administered daily for eight weeks. The body weight, motor nerve conduction velocity, motor distal latency and mixed nerve conduction velocity were measured before administration, after two, four, six and eight weeks' administration.