The following abstract presents results of a study conducted by a contract laboratory for the National Toxicology Program (NTP). The findings may or may not have been peer reviewed and were not evaluated in accordance with the Explanation of Levels of Evidence for Reproductive Toxicity criteria (see http://ntp.niehs.nih.gov/ntp/htdocs/levels/09_3566_NTP_ReproTOX_R1.pdf or with the Explanation of Levels of Evidence for Developmental Toxicity criteria (see http://ntp.niehs.nih.gov/ntp/Test_info/NTP_DevTox20090507.pdf) established by the NTP in March 2009. The findings and conclusions for this study should not be construed to represent the views of the NTP or the US Government.
Di(n-butyl) phthalate (DBP) was evaluated using the "Reproductive Assessment by Continuous Breeding" protocol and Swiss CD-1 mice. In the present study, Task 1 (dose range finding) was not performed since sufficient data were available in the literature to select dose levels for Task 2 (continuous breeding).
Dietary levels of 0.0, 0.03, 0.3 and 1.0% DBP (greater than or equal to 99% pure) were employed in Task 2. Continuous exposure of CD-l mice (11 weeks of age at outset) to the 1.0% dietary level of DBP significantly diminished (p< 0.01) the number of breeding pairs able to produce at least one litter as compared to the control pairs. In contrast, the 0.03 and 0.3% dietary levels of DBP had no effect on the fertility of breeding pairs. DBP at the highest dietary level (1.0%) also significantly decreased the number of litters delivered per pair, the average litter size, and the proportion of pups born alive as compared to the control and two lower dose groups. In addition, the proportion of live males per litter (males/total) was significantly greater in the 1.0% DBP group versus the control, and the 0.03 and 0.3% DBP groups, implying that male fetuses may be slightly more resistant to the toxic effects of DBP than female fetuses. Further, live pup weight adjusted for the total number of pups per litter tended to be lower for the pairs receiving the 1.0% DBP diet as compared to the pairs fed the control, 0.03% DBP, or 0.3% DBP diets.
Since DBP exerted significant deleterious effects on fertility and reproductive performance in the F0 breeding pairs (Task 2), it was decided to conduct a crossover mating trial with the control and high dose F0 mice in order to determine whether one or both sexes were adversely affected (Task 3). Three combinations of breeding pairs were utilized in the crossover mating trial immediately following the 18- week exposure period in Task 2. These were: Control male x Control female, 1.0% DBP male x Control female, and Control male x 1.0% DBP female. Although the proportion of detected matings did not differ significantly across the three combinations of breeding pairs, the proportion fertile was significantly reduced in the Control male x 1.0% DBP female pairing versus the Control male x Control female and 1.0% DBP male x Control female pairings. In addition, the number of live pups per litter, the proportion of pups born alive, and the absolute and relative live pup weights were significantly decreased for the Control male x 1.0% DBP female pairs as compared to the other two combinations of breeding pairs. As observed initially for the F0 pairs fed the 1.0% DBP diet, the proportion of live males per litter (males/total) in Task 3 tended to be higher for the Control male x 1.0% DBP female pairs relative to the other two pairings. Taken together, these data clearly show that the female parent and her offspring in utero were selectively affected by exposure to 1.0% DBP in the diet.
The control and 1.0% DBP-exposed F0 mice were necropsied 26 days after the completion of the 7-day crossover mating trial. Sperm assessment indicated no significant difference in the % motile sperm, sperm concentration, or % abnormal sperm in the cauda epididymis between male mice exposed to 0.0 or 1.0% DBP in the diet. On the other hand, body weight was significantly decreased and the relative liver weight was significantly increased in the male mice fed the 1.0% DBP- containing diet versus male mice given the control diet. In the F0 females, absolute and relative liver weight was significantly increased and absolute and relative uterine weight was significantly decreased in the 1.0% DBP-exposed group versus the combined control group. No treatment related gross or histopathologic lesions were noted for the testis, epididymis, prostate or seminal vesicles in male mice, or for the ovary, oviduct, uterus, or vagina in the female mice. Histological evaluation of the cell types in the vaginal mucosa indicated that there were no treatment-related effects on the estrous cycle.
Under the conditions of this study, 1.0% DBP in the diet was a reproductive toxicant in female CD-l mice as evidenced by decreased fertility, decreased number of litters, decreased number of live pups per litter, decreased proportion of pups born alive, decreased live pup weights, and an increased proportion of live males per litter (males/total). Uterine weight also was significantly lower in 1.0% DBP exposed females versus controls, perhaps reflecting the production of fewer and smaller litters in the DBP-treated group. Finally, liver weights were greater in 1.0% DBP-exposed males and females and body weight was significantly decreased in 1.0% DBP-fed males as compared to these same endpoints in control male and female mice.Thus, DBP is a reproductive toxicant in the presence of systemic toxicity.
Report Date: November 28, 1984