Dibutyl phthalate

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: well documented and scientifically acceptable, but lacking guidelines

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2000

Report date:

1999

Materials and methods

Principles of method if other than guideline:

No guideline specified, cf. "Any other information on material and methods" for details.

GLP compliance:

not specified

Test material

Test material information

Constituent 1

Reference substance name:

Dibutyl phthalate

EC Number:

201-557-4

EC Name:

Dibutyl phthalate

Cas Number:

84-74-2

Molecular formula:

C16H22O4

IUPAC Name:

dibutyl phthalate

Details on test material:

DBP: 99% pure, Tokyo Kasei Kogyo Co., Ltd., Tokyo, Japan

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

Wistar rats (Jcl: Wistar, CLEA Japan Inc., Tokyo, Japan) were used throughout this study. Animals were reared on a basal diet (F-1; Funabashi Farm Co., Funabashi, Japan) and tap water ad libitum and maintained in an air-conditioned room at 24 1°C, with a relative humidity of 55 5%, under a controlled 12-h light/dark cycle. Vaginal smears of each rat were recorded daily, and only rats showing at least 2 consecutive 4-day cycles were used in the experiments.

Administration / exposure

Route of administration:

other: gastric intubation

Vehicle:

olive oil

Duration of treatment / exposure:

GD 0-8

Frequency of treatment:

once daily

Duration of test:

until GD 20

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 250, 500, 750, 1000, 1250, 1500 mg/kg
Basis:

No. of animals per sex per dose:

13
10-13 in the pseudopregnant rats experiment

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

body weight, food consumption

Ovaries and uterine content:

weight measure

Fetal examinations:

litters resorbed, corpora lutea, preimplantation loss, postimplantation loss

Statistics:

Analysis of variance and Dunnett’s multiple comparison test, Kruskal–Wallis test and Mann–Whitney test or Fisher’s exact test were used as appropriate.

Historical control data:

yes, cf. remarks

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Effect levels (maternal animals)

Dose descriptor:

LOAEL

Effect level:

750 mg/kg bw/day (nominal)

Basis for effect level:

pre and post implantation loss

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:yes

Effect levels (fetuses)

Dose descriptor:

LOAEL

Effect level:

500 mg/kg bw/day (nominal)

Basis for effect level:

fetal/pup body weight changes

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Administration of DBP to pregnant rats

No deaths were seen in any groups (Table 1). The female rats in the DBP-treated groups at higher doses showed reddish staining of the facial fur and/or piloerection. The body weight gain and food consumption on Days 0 to 9 in the groups given DBP at 500 mg/kg and above were significantly lower than those in the control group. A significantly lower body weight gain on Days 9 to 20 was found at 1500 mg/kg. There was no significant difference between the DBP-treated groups and the control group in the adjusted weight gain, which indicates the net weight gain of female rats.

After successful mating, all females in the control group and 250, 500, 750, and 1000 mg/kg groups become pregnant (Table 2). Total absence of any implantation site, i.e., nonpregnancy, was found in 5 of the 13 females at 1250 mg/kg and 7 of the 13 females at 1500 mg/kg, and the pregnancy rate in these groups was significantly lower than that in the control group. A significantly decrease in the number of implantations per female at 1250 and 1500 mg/kg and a significantly increase in the incidence of preimplantation loss per female at 1250 and 1500 mg/kg were observed. In females having implantations, there was no significant difference between the DBP-treated groups and the control group in the numbers of corpora lutea and implantations per litter. A significantly higher number of resorptions and dead fetuses per litter at 1000 mg/kg and above and a significantly lower number of live fetuses per litter at 750 mg/kg and above were observed. The incidences of preimplantation loss per litter in the 1500 mg/kg group and of postimplantation loss per litter in the 750, 1000, 1250, and 1500 mg/kg groups were significantly higher than those in the control group. A significantly lighter body weight of live fetuses was observed at 500 mg/kg and above.

Administration of DBP to pseudopregnant rats

No deaths were seen in any groups (Table 3). The pseudopregnant rats in the DBP-treated groups at higher doses showed reddish staining of the facial fur and/or piloerection. The body weight gain on Days 0–9 in the groups given DBP at 750 mg/kg and above was significantly lower than that in the control group. The food consumption on Days 0–9 in the groups given DBP at 500 mg/kg and above was significantly lower than that in the control group.

The ovarian weights of rats sacrificed on Day 9 of pseudopregnancy are shown in Fig. 1. A significantly lower weight was found in the 1250 and 1500 mg/kg groups when compared to the control group.

Fig. 2 represents the number of corpora lutea per female sacrificed on Day 9 of pseudopregnancy. There was no significant difference in the number of corpora lutea per female between the DBP-treated groups and the control group.

The uterine weights of rats sacrificed on Day 9 of pseudopregnancy are presented in Fig. 3. Decrease in the uterine weight was found in pseudopregnant rats given DBP. The uterine weight in the groups given DBP at 750 mg/kg and above was significantly lower than that in the control group, and a remarkably lower weight of the uterus was found at 1250 and 1500 mg/kg.

The serum progesterone levels in pseudopregnant rats sacrificed on Day 9 are shown in Fig. 4. The serum progesterone level in the 1500 mg/kg group was significantly lower than that in the control and sham-operation groups.

The serum estradiol levels in pseudopregnant rats sacrificed on Day 9 are presented in Fig. 5. The serum estradiol level in the DBP-treated groups was not significantly different from that in the control and sham-operation groups.

Applicant's summary and conclusion

Conclusions:

DBP caused significant increases in the incidences of preimplantation loss in females successfully mated at 1250 and 1500 mg/kg and of postimplantation loss in females having implantations at 750 mg/kg and above. The uterine decidualization in pseudopregnant rats was significantly decreased at 750 mg/kg and above. These findings suggest that early embryonic loss due to DBP may be mediated, at least in part, via the suppression of uterine decidualization, an impairment of uterine function.

Executive summary:

In this study, the effects of DBP on reproductive function were investigated on pregnant and pseudopregnant rats. Rats were given DBP by gastric intubation at 0, 250, 500, 750, 1000, 1250 or 1500 mg/kg on Days 0 to 8 of pregnancy and the pregnancy outcome was determined on Day 20 of pregnancy. The same doses of DBP were given to pseudopregnant rats, with an induced decidual cell response, on Days 0 to 8 of pseudopregnancy, and the uterine weight on Day 9 served as an index of the uterine decidualization.