Modified One-Generation Study:

F₀ exposure began on GD 6 and was continual. At weaning on postnatal day (PND) 28, F₁ offspring were assigned to either reproductive performance (2/sex/litter), prenatal (1/sex/litter), or biological sampling (1/sex/litter) cohorts. Upon sexual maturity, F₁ mating and pregnancy indices were evaluated. In the prenatal cohort, F₂ prenatal development (litter size, fetal weight, and morphology) was assessed on GD 21. In the reproductive performance cohort, littering indices, F₂ viability, and growth were assessed until PND 28. The likelihood of identifying potential 2H4MBP-induced adverse effects (similarity and magnitude thereof) at any phase of growth or development was increased by examining related endpoints in multiple pups within a litter throughout life, across cohorts, and across generations.

2H4MBP exposure at the tested concentrations did not induce any effects on mating or pregnancy indices. In the prenatal cohort, exposure to 30,000 ppm was associated with a slight but significant decrease in the mean numbers of corpora lutea and F₂ implants and a slightly lower number of live fetuses on GD 21 than in the control group. In the reproductive performance cohort, total F₂ mean litter size on PND 0 was also significantly decreased compared to the control group. 2H4MBP exposure might have affected litter size, although the effect was small in magnitude. Collectively, given the minimal apparent response that may or may not be a direct effect of 2H4MBP, this was considered equivocal evidence of an adverse effect on reproductive performance. EE exposure did not affect F₁ live litter size on PND 0, but significantly decreased mean number of corpora lutea and total F₂ implants were observed.

2H4MBP was associated with lower F₁ and F₂ preweaning and F₁ postweaning mean body weights. At 30,000 ppm 2H4MBP, preweaning F₁ mean body weights of both males and females were progressively lower over time, relative to their respective control groups. The response was lessened in F₂ males and even more so in F₂ females. The significantly decreased F₁ postweaning mean body weights were not associated with concurrent lower feed consumption. The effects on body weights associated with exposure to 2H4MBP were considered some evidence of developmental toxicity. 2H4MBP intake by F₀ females in the 3,000, 10,000, and 30,000 ppm 2H4MBP groups, based on feed consumption and dietary concentrations from GD 6 through GD 21 was approximately 205, 697, and 2,644 mg/kg/day, respectively; from LD 1 through LD 13, 2H4MBP intake was approximately 484, 1,591, and 5,120 mg/kg/day, respectively. 2H4MBP intake by the F₁ generation postweaning (PND 28 through PND 91) in the 3,000, 10,000, and 30,000 ppm groups was approximately 267, 948, and 3,003 mg/kg/day (males) and 287, 983, and 3,493 mg/kg/day (females), respectively. 2H4MBP intake by the adult F₁ females in the 3,000, 10,000, and 30,000 ppm groups was approximately 240, 825, and 2,760 mg/kg/day (GD 0 through GD 21) and 426, 1,621, and 5,944 mg/kg/day (LD 1 through LD 13), respectively.

Diaphragmatic hernias were observed at a low incidence in 2H4MBP-exposed animals in both the F₁ and F₂ generations but were not observed in any control animals. Most of the diaphragmatic hernias were associated histologically with hepatodiaphragmatic hernias. Low incidences of diaphragmatic and hepatodiaphragmatic hernias have been reported in control groups in other NTP MOG studies. Therefore, it is unclear whether the occurrences of diaphragmatic and hepatodiaphragmatic hernias in both the F₁ and F₂ generations were related to 2H4MBP exposure.

2H4MBP did not alter estrogen or androgen-mediated developmental markers, and no gross lesions were observed at adult necropsy consistent with perturbation of normal estrogen receptor- or androgen-receptor-mediated development. Expected estrogenic responses were observed in the EE group. In the 30,000 ppm group, adult weights of male androgen-dependent reproductive tissues were slightly lower than those of the control males, likely secondary to the apparent growth retardation, and occurred in the absence of histopathological findings. Sperm and spermatid counts were not affected by 2H4MBP exposure. The ability of F₁ males in either cohort to successfully mate, resulting in pregnancy, also was not affected. Unlike findings reported for in vitro cell models, 2H4MBP had no apparent effect on estrogen receptor- or androgen-receptor-dependent processes, nor did it affect mating or pregnancy indices.

2H4MBP exposure in F₁ rats was associated with significantly increased kidney weights, renal tubule epithelial regeneration, interstitial chronic active inflammation, renal tubule and pelvic concretions, renal tubule dilation, papillary necrosis, urothelial hyperplasia, and urothelial ulcers. F₁ females also displayed renal tubule epithelial degeneration, pelvic dilation, chronic progressive nephropathy, and mineralization. 2H4MBP-exposed F₁ males and females displayed significantly increased liver weights relative to their respective control groups. The absolute weight of the adrenal glands was significantly decreased in the 30,000 ppm female group relative to the control group in the reproductive performance cohort. Several other decreases in organ weights were not associated with histological correlates and were considered related to changes in body weights.

F₂ fetal findings of hydronephrosis of the kidney and enlarged liver were observed in the 30,000 ppm group. F₂ offspring in the 30,000 ppm group exhibited dilation of the renal pelvis. The observed fetal, PND 28, and adult necropsy findings were consistent with previously reported studies that identified the kidney and liver as target tissues of 2H4MBP-mediated toxicity.

Conclusions:

Under the conditions of this modified one-generation (MOG) study, there was equivocal evidence of reproductive toxicity of 2-hydroxy-4-methoxybenzophenone (2H4MBP) in Hsd:Sprague Dawley^® SD^® rats based on a decrease in F₂ litter size in both the prenatal and reproductive performance cohorts.

Under the conditions of this MOG study, there was some evidence of developmental toxicity of 2H4MBP in Hsd:Sprague Dawley^® SD^® rats based on the observed postnatal growth retardation. The relationship of the increased occurrence of diaphragmatic and hepatodiaphragmatic hernias in F₁ adults and F₂ pups to 2H4MBP exposure is unclear.

Exposure to 2H4MBP was not associated with signals consistent with alterations in estrogenic, androgenic, or antiandrogenic action. Exposure to 2H4MBP was associated with lower F₁ and F₂ mean body weights; this effect on body weight contributed to the apparent 2H4MBP-related decreases in male reproductive organ weights. Mating and littering were not significantly affected by 2H4MBP exposure. Exposure to 2H4MBP was associated with nonneoplastic kidney lesions in the F₀, F₁, and F₂ generations. Expected estrogenic responses were observed in the EE group.