Norethisterone

Genetic toxicity: in vivo

Administrative data

Endpoint:

genetic toxicity in vivo, other

Remarks:

chromosomal aberration assay and micronucleus test

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 Type:

publication

Title:

Progestin (norethisterone)-induced genetic damage in mouse bone marrow

Author:

Shyama SK, Rahiman MA

Year:

1993

Bibliographic source:

Mutation Research, 300 (1993) 215-221

Materials and methods

Principles of method if other than guideline:

8-10-week-old healthy female Swiss mice (average body weight 25 g) were administered doses of 0.3, 1.5, 3.0, 6.0, 12.0, 18.0, 24.0 and 30.0 mg/kg body weight test item for 15 consecutive days by gavage.

Chromosome analysis
Mice were injected intraperitoneally with 0.2 ml of 0.025% colchicine, 1.5 h before they were killed by cervical dislocation. Bone marrow chromosomal preparations were made according to the method of Tjio and Whang (1962), using 0.56% potassium chloride as hypotonic solution. 100 metaphase spreads per animal were analysed. Breaks were identified as unstained regions present along the chromatids wider than the thickness of the chromatids that bear them. Transfer of the terminal portion of one chromosome to another leading to unequal length of arms was scored as a translocation. Improper spreading with stickiness and clumping of chromosomes was identified as stickiness. The extreme of stickiness represented by sticky degeneration of the chromosome was noted as pulverisation. Stickiness and pulverisations were scored together. The mitotic index (MI) was calculated by analysing 2000 cells per animal.

Micronucleus test
Experimental animals were killed at different time intervals. Bone marrow preparations were made according to the method of Schmid (1973), with a slight modification, i.e., the fetal calf serum was replaced by 5% bovine albumin solution in phosphate-buffered saline (PBS) (Seetharama Rao et al., 1983). Smears were stained with May-Grünwald Giemsa and analysed for the presence of MN in both polychromatic erythrocytes (PCEs) and normochromatic erythrocytes (NCEs). 2000 PCEs and the corresponding number of NCEs per animal were analysed for the presence of MN. The ratio of PCEs to NCEs (P/N) was calculated for all treated and control groups.

GLP compliance:

not specified

Type of assay:

other: chromosomal aberration assay and micronucleus test

Test material

Test material information

Constituent 1

Reference substance name:

Norethisterone

EC Number:

200-681-6

EC Name:

Norethisterone

Cas Number:

68-22-4

Molecular formula:

C20H26O2

IUPAC Name:

17α-Ethynyl-17ß-hydroxy-4-estren-3-one

Test animals

Species:

mouse

Strain:

Swiss

Sex:

female

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

water

Duration of treatment / exposure:

15 d

Frequency of treatment:

daily

Doses / concentrations

Remarks:

0.3, 1.5, 3.0, 6.0, 12.0, 18.0, 24.0 and 30.0 mg/kg body weight

No. of animals per sex per dose:

3

Control animals:

yes, concurrent vehicle

Positive control(s):

cyclophosphamide

Examinations

Tissues and cell types examined:

bone marrow

Results and discussion

Test results

Test results 1

Sex:

female

Genotoxicity:

negative

Remarks:

micronucleus assay

Vehicle controls validity:

valid

Positive controls validity:

valid

Test results 2

Sex:

female

Genotoxicity:

positive

Remarks:

chromosome aberration assay

Vehicle controls validity:

valid

Positive controls validity:

valid

Applicant's summary and conclusion

Conclusions:

equivocal

Executive summary:

Norethisterone was assessed for their in vivo genotoxic effect on the bone marrow cells of Swiss albino mice. The chromosomal aberration assay and the micronucleus test were employed for the study.

Dose-response analysis was carried out for the above doses 24 h after the final feeding (15 d; 0.3, 1.5, 3.0, 6.0, 12.0, 18.0, 24.0 and 30.0 mg/kg body weight). Time-response studies were done using mice fed 3.0 mg/kg/day, 6, 12, 24, 48, 96 h and 1, 2 and 3 weeks after the final feeding.

No treatment-related effect on the rate of micronuclei was observed after any of the doses. In addition, no increase of the incidence of chromosome breaks or chromosomal translocations which were designated as "classical" chromosomal aberrations were noted.

However, the incidence of so-called "non-classical" chromosomal aberrations such as "stickiness" and "pulverisations" was increased from 3.0 mg/kg/day onwards. Similar findings were said to occur in studies on the natural steroid progesterone. These "non-classical" findings weretransientwith a maximum at 12 and 24 hours after the final treatment and a sharp decline thereafter. A possible drug interaction with the nucleoproteins was discussed as one possible underlying mechanism which should account for the absence of a concomitant effect on the rate of micronuclei.