Mechanism of Developmental Effects in Rats Caused by an N-Phenylimide Herbicide: Transient Fetal Anemia and Sequelae during Mid-to-Late Gestation.

BACKGROUND: Rat developmental toxicity including embryolethality and teratogenicity (mainly ventricular septal defects [VSDs] and wavy ribs) was produced by an N-phenylimide herbicide that inhibits protoporphyrinogen oxidase (PPO) common to chlorophyll and heme biosynthesis. Major characteristics of the developmental toxicity included species difference between rats and rabbits, compound-specific difference among structurally similar herbicides, and sensitive period. Protoporphyrin accumulation in treated fetuses closely correlated with the major characteristics. Iron deposits in erythroblastic mitochondria and degeneration of erythroblasts were observed in treated rat fetuses. In this study we investigated fetal anemia and subsequent developmental effects in rats, and inhibition of PPO in rats, rabbits, and humans by the herbicides in vitro. METHODS: Fetuses were treated on gestational day (GD) 12 and removed on GDs 13 through 20. All litters were examined externally. One half of litters were examined for blood and skeletal development, and the other half for interventricular foramen closure. Effects on PPO were determined in mitochondria from embryos and adult livers. RESULTS: Fetal anemia in rats was evident on GDs 13 through 16. Subsequently, enlarged heart, delayed closure of the foramen, reduced serum protein, and retarded rib ossification were observed. In vitro PPO inhibition exhibited species- and compound-specific differences corresponding to the developmental toxicity. CONCLUSION: We propose that developmental toxicity results from PPO inhibition in primitive erythroblasts, causing transient fetal anemia followed by death. Compensatory enlargement of the fetal heart results in failure of interventricular foramen closure and VSD. Reduced serum protein leads to delayed ossification and wavy ribs.

Maternal exposure to procymidone has no effects on fetal external genitalia development in male rabbit fetuses in a modified developmental toxicity study.

This study was conducted to evaluate the effects of procymidone (PCM) on development of male rabbit fetal external genitalia. PCM was administered once daily by gavage at dose levels of 0 (control) and 125mg/kg/day to pregnant rabbits from gestation day 6 through 28 and fetal external genitalia was observed in detail. This treatment period covered the critical stage of sexual differentiation of fetal external genitalia in rabbits. In the maternal animals, food consumption was reduced in the PCM group. There were no effects of PCM on maternal caesarean sectioning data or fetal external observations. In fetal external genitalia observations, there were no significant differences between the control and PCM treatment group in any of the following parameters: ano-genital distance (AGD), phallus boundary-genital distance, diameter of preputial lamella, ventral gap of preputial lamella, or ventral gap to diameter ration of preputial lamella, though severe feminization such as decreasing of AGD and hypospadias in male rat offspring at the dose level of 125 mg/kg of PCM were reported. These results suggest that PCM has no effect on fetal external genitalia development in male rabbit fetuses, and species difference of developmental effects of PCM on sexual differentiation exists.

New method for detecting antiandrogenic effects through the measurement of external genitalia in rabbits.

The aim of the present study was to develop a quantitative evaluation method for detecting antiandrogenic activity of chemicals in rabbits that are regularly used for developmental toxicity studies. Kbl: New Zealand White rabbits (n = 8-9) were injected intramuscularly with an antiandrogen, cyproterone acetate (CA; 10 mg/kg body weight [BW]/day), on gestation days (GD) 13-24. On GD 29, live fetuses were obtained by cesarean section and sexed by examination of the internal genitalia. The external genitalia were evaluated in cross-section measurements of the phallus by both diameter and width of the ventral gap of the preputial lamella with a micrometer under a stereoscopic microscope. The diameters of the preputial lamella were 1015 +/- 83.5, 856 +/- 64.0, and 865 +/- 72.6 microm in control males, control females, and CA-treated males, respectively. The ventral gaps of the preputial lamella were 26 +/- 8.2, 437 +/- 72.3, and 318 +/- 59.4 microm in the control males, control females, and CA-treated males, respectively. There were statistically significant differences in both parameters between control males and control females or CA-treated males. The lower fetal BW in CA-treated males did not disturb the detection of the feminization of the ventral gap of the preputial lamella; however, the diameter of the preputial lamella might be influenced by fetal BW because no difference in the relative diameter of the preputial lamella was found between control males and CA-treated males. These results demonstrated that this approach could detect the antiandrogen activity of CA quantitatively by feminization of male external genitalia in rabbit fetuses.