In Utero 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) Alters Reproductive Morphology and Function in Female Rat Offspring

Exposure to pesticides or toxic substances that disrupt the endocrine system during sex differentiation can permanently alter reproductive function and produce morphological pseudohermaphrodism. While some developmental toxicants affect either the male or the female, in utero exposure to 0.5 μg TCDD/kg/day from Gestational Day (GD) 6 to GD 15 induces infertility in both sexes (K. S. Khera and J. A. Ruddick, Chlorodioxins-Origin and Fate, pp. 70-84, Am. Chem. Soc., Washington, DC, 1973). Although a number studies have focused on the effects of a single dose of TCDD on sex differentiation of the male rat and hamster, the reproductive alterations that account for female-mediated infertility after in utero exposure to TCDD have not been described. Hence, it was our objective to describe the anatomical and functional reproductive alterations in female progeny after gestational administration of TCDD. In the first experiment, LE Hooded rats were given a single dose of 1 μg TCDD/kg by gavage on GD 8 (i.e., a period that includes major organogenesis) or GD 15 (i.e., a period prior to sex differentiation and a dosing regime that alters sex differentiation of the male LE rat). In a second experiment, Holtzman rats were dosed with TCDD at 1 μg/kg on GD 15, to determine if the progeny of this strain displayed malformations of the external genitalia and vaginal orifice as did LE rats. TCDD-treated female LE offspring displayed a number of unusual reproductive alterations. In the GD 15 group, puberty was delayed, more than 65% of the female offspring displayed complete to partial clefting of the phallus, and 80% displayed a permanent "thread" of tissue across the opening of the vagina. In the GD 8 treatment group, 25% displayed partially cleft phallus and 14% had a vaginal thread. GD 15 TCDD administration also induced a high incidence of malformations in Holtzman female progeny (100% clefting and 83% with a vaginal thread). At necropsy ( >550 days old), ovarian weight was significantly reduced by 23% in both rat strains. In the LE rat, vaginal and behavioral estrous cyclicity, estrous cycle-mediated running wheel activity, and female sexual behaviors at proestrus (darting and lordosis to mount ratios) were not affected by gestational GD 15 TCDD treatment. However, untreated stud males had difficulty attaining intromission and took longer to ejaculate and vaginal bleeding was displayed during mating by GD 15 TCDD-exposed female offspring. GD 8 TCDD-treated female offspring displayed enhanced incidences of constant estrus (CE) (47% CE in GD 8 versus 16% CE in the control and GD 15 groups at middle age) and cystic endometrial hyperplasia. In addition, in the GD 8 group the fertility rate declined significantly faster than in controls (p < 0.02) and fecundity was reduced by 38% (p < 0.07). In conclusion, administration of a single dose of 1 μg TCDD/kg on GD 15 results in malformations of the external genitalia in female LE and Holtzman rats. While GD 15 treatment is generally more toxic than GD 8 to the offspring with respect to growth, viability, male reproductive effects (L. E. Gray, W. R. Kelce, E. Monosson, J. S. Ostby, and L. S. Birnbaum, Toxicol. Appl. Pharmacol.131, 108-118, 1995) and malformations of the external genitalia in the female progeny, treatment on GD 8 is more effective in inducing functional reproductive alterations in female progeny.