Octamethylcyclotetrasiloxane

Toxicity to reproduction: other studies

Administrative data

Endpoint:

toxicity to reproduction: other studies

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

27.10.1997 to 14.06.1999

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

1999

Report date:

1999

Reference 2

Reference Type:

publication

Title:

An inhalation reproductive toxicity study of octamethylcyclotetrasiloxane (D4) in female rats using multiple and single day exposure regimens.

Author:

Meeks, RG, DG Stump, WH Siddiqui, JF Holson, KP Plotzke, and VL Reynolds

Year:

2007

Bibliographic source:

Reproductive Toxicology 23: 192-201.

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

This study was conducted to evaluate the temporal responsiveness of female rats to the reproductive effects of D4.

GLP compliance:

yes

Type of method:

in vivo

Test material

Test material information

Constituent 1

Reference substance name:

Octamethylcyclotetrasiloxane

EC Number:

209-136-7

EC Name:

Octamethylcyclotetrasiloxane

Cas Number:

556-67-2

Molecular formula:

C8H24O4Si4

IUPAC Name:

2,2,4,4,6,6,8,8-octamethyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Administration / exposure

Route of administration:

inhalation

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Analytical verification of doses or concentrations:

yes

Duration of treatment / exposure:

Pre-mating phase: 1) a single 6-h exposure, one day prior to, two days prior to, three days prior to, or four days prior to mating (Groups 2-5; a total of 125 females). 2) daily 6-h exposures from three days prior to mating through one day prior to mating (Group 6; 125 females). 3) daily 6-h exposures starting three days prior to mating and continuing through a two-day mating interval and gestation through gestation day 3 (Group 7; 70 females).
Post-mating phase: 1) single 6-h exposure on gestation day 0, 1 or 2 (Groups 2-4, 25 females/group). 2) daily 6-h exposures from gestation day 0 through gestation day 2 (Group 5, 25 females).

Frequency of treatment:

Multiple and Single Day Exposure Regimens

Duration of test:

Five weeks

Doses / concentrations

Dose / conc.:

700 ppm (analytical)

No. of animals per sex per dose:

Various depending on group.

Control animals:

other: concurrent treatment with filtered air

Details on study design:

This experiment focused on the fertilization and implantation phases to  further define the temporal responsiveness of the effects seen following  exposure to D4 during these phases. All exposures were 6 h/day at a D4  concentration of 0 or 700 ppm.  In the pre-mating phase, rats were  exposed to D4 as a single 6 h exposure 1, 2, 3, or 4 days prior to mating  (days-1-4 groups, respectively); or daily for 3 days prior to mating  through 1 day prior to mating (days-3-1); 
or daily beginning 3 days prior  to mating and continuing through gestation day 3 (day-3 through GD 3). In  the Post-mating phase, groups were exposed to test article as a single 6  h exposure on gestation days 0, 1, or 2 (GD 0, GD1, or GD2 groups,  respectively). The last group was exposed from GD 0-2 (GD 0-2).   Following exposure, females in the pre-mating phase were paired on a 1:1  basis with unexposed male rats. Positive evidence of mating was 
confirmed  by the presence of sperm in a vaginal smear or a copulatory plug and that  day was termed GD0. The experimental design of the post-mating phase  consisted of four exposure groups and 1 control group, with 25 females in  each group. The bred females were consecutively assigned in a block  design to groups containing 25 rats each by the following procedure. The  first mated female and the appropriate GD 0 designation were recorded 
and  the female was assigned to group 1, the second mated female was assigned  to group 2, and the third to group 3, etc. This process was continued  daily until 25 females were placed into each group. Individual body  weights were measured on GD0, 4, and 8 for all females. All females were  euthanized by 
intravenous injection of sodium pentobarbital via a tail  vein on GD 8 and the thoracic, abdominal, and pelvic cavities examined.  The uterus of each dam was excised, and the number of CL on each ovary  and the total number of implantation sites were recorded. The individual  uterine distribution of implantation sites was documented. During the  uterine examination, some of the implantation sites appeared to be  atypically small and it was hypothesized that the smaller implantation  sites may have been an indication of a delay in uterine implantation.  Based on this observation, the implantation site that appeared to be  small in size by visual inspection was measured using calipers. To  provide an estimate of the diameter of a normal gestation day 8 implant,  all implantation sites were measured for five control females with  implantation site counts of 17-19 sites/dam. Based on the mean diameter  of the implantation sites from these five control group females (4.5 mm),  it was decided that measured implantation sites that were less than 3.6mm  in diameter would be considered to be small.  Uteri with no macroscopic  evidence of implantation were placed in 10% ammonium sulfide for  detection of early implantation loss. The uterus and ovaries from all  females were weighed and preserved in 10% neutral buffered formalin for  possible histopathological evaluation. Other maternal tissues were  preserved in 10% neutral buffered formalin for possible histopathological  examination only as indicated by the gross findings. Microscopic  examinations were performed on all small implantation sites detected in  this study and on representative implantation sites present in uteri from  control group females. The ovaries from dams treated on day-1 (i.e.,  proestrus) along with ovaries from their concurrent control group were  also evaluated.

Statistics:

All analyses of reproduction group female data were conducted for a  minimum significance level of 5% comparing each treated group to the  control group; all means are presented with standard deviations (S.D.). All tests for significance at the 5% probability level were two-tailed  for the group comparisons. The litter was used as the experimental unit.  An analysis of variance (two-tailed) with  Dunnett's test was used to compare pre-coital intervals, maternal body  weight data, gravid uterine weights, viable fetuses, implantation sites,  corpora lutea, and organ weights (absolute and relative to final body  weights). The Kruskal-Wallis test with the Mann-Whitney U-test was used  for litter proportions of intrauterine data (considering the litter, rather than the fetus, as the experimental unit).

Results and discussion

Effect levels

Dose descriptor:

NOAEL

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Reduced food consumption and body weight gain, and reduced number of corpora lutea and implantation sites.

Remarks on result:

not determinable

Remarks:

no NOAEL identified

Observed effects

All females in the pre-mating and post-mating phases survived to scheduled necropsy on GD 8. No exposure-related clinical observations or internal findings (exclusive of the reproductive tract) were noted in females from either phase. In the pre-mating phase, the fertility index (number gravid/number 
with evidence of mating) in the females exposed 1 day prior to mating was significantly reduced relative to the control group value (64.7% in the day-1 group, as compared to 95.5% in the  control group). The fertility indices were unaffected by exposure in the  other pre-mating phase groups. In the post-mating phase, fertility indices were unaffected by test article exposure. In the pre-mating phase, the mean numbers of corpora lutea were significantly reduced only in the day-3 through GD3 group. The mean number of implantation sites in this group was decreased, when compared with the controls, although statistical significance was not achieved. In the days-1 to -4, and -3 to -1 groups, the mean numbers of corpora lutea and implantation sites were unaffected by exposure.
Pre-implantation loss  was unaffected by exposure under all pre-mating phase treatment regimens. An increased number of small implantation sites was observed in the day-3  throughGD3 group. The numbers of small implantation sites in the other exposed groups were similar to the control group value. In the  post-mating phase, mean numbers of corpora lutea and implantation sites, pre-implantation loss, and numbers of small implantation sites were unaffected by test article exposure under all treatment regimens. In the pre-mating phase, absolute mean uterine weights were significantly  reduced (19.8%) in the day-3 through GD 3 group.  The reductions in the  mean uterine weights were consistent with the reduced number of total  implantation sites and the increased number of small implantation sites in this group. The mean absolute and relative ovarian weights in this group were unaffected by exposure. Mean uterine and ovarian weights were unaffected by exposure in all other pre-mating phase groups and in all post-mating phase groups. In the pre-mating phase, the ovaries from all females in the day-1 group had a normal complement of corpora lutea. All were consistent with the corpora lutea of pregnancy (11 rats) or pseudo pregnancy (six non-pregnant rats).

Any other information on results incl. tables

The analysed mean exposure concentration for the 700 ppm target concentration for both the pre-mating phase and the post-mating phase was 700 ppm.

Applicant's summary and conclusion

Conclusions:

In a reproductive toxicity study conducted to GLP (reliability score 1) in which female rats were exposed to D4 on multiple and single day exposure regimens, toxicity was expressed in the pre-mating phase by a reduced pregnancy rate in Group 2 (the Day-1 group), by effects on mean body weight gains in Group 6 (the days -3 through -1 group), and by effects on mean body weight gains, reduced food consumption, reduced numbers of corpora lutea and implantation sites, increased numbers of small implantation sites, and reduced mean uterine weight in Group 7 (the day -3 through GD3 group). Toxicity was expressed in the post-mating phase by reduced mean body weight gain and food consumption in Group 5 (the GD0-2 group).