Developmental, behavioral and endocrine alterations in male rats at early and late postnatal life following in utero exposure to low dose di- n-butylphthalate

Abstract

Environmental chemical pollutants that interfere with hormonal homeostasis or hormone signaling are the relevant agents inducing congenital or postnatally developed reproductive abnormalities in human beings, wild and domestic animals. In this study, we are examining reproductive effects of prenatal exposure of male rats to a low dose di-n-butylphthalate (DBP). Wistar female rats were given intragastrically DBP at a daily dose of 100 mg/kg b.w. during 15th-21st days of pregnancy. Anogenital distance (AGD) in male offspring decreased on postnatal day (PND) 2 followed by its normalization on PND 7 and 10. There were no other visible teratogenic lesions in the newborns. The testicle descent into scrotum of control males occurred on PND 38.5 ± 0.1, while in DBP group it accelerated by 5.3 days on the average. At the age of 6 months, DBP-exposed animals exhibited double increase of blood plasma testosterone level as compared to controls, and hyperactive male sexual behavior in the presence of receptive female. The duration of latent periods of the first mount and the first intromission, as well as post-ejaculatory refractory period, have been shortened; the number of mounts with intromission and the number of ejaculations increased significantly. Histological examination of the testes indicated activation of Leydig cells. The female-type sexual behavior as evaluated by appearance of lordosis of orchidectomized and primed with estradiol and progesterone 10-month-old males in response to mount or approach of sexually active normal male was enhanced in DBP-group. Both 10-month-old and aging males (18 months), castrated and hormone-primed, displayed homosexual type of behavior. Prenatal low dose DBP caused in 18-month-old males premature atrophy of the testes and accessory sexual glands, increased number of Leydig cell adenomas, a twice decrease of plasma testosterone level and exhausting of sexual potency. We concluded that prenatal exposition of male rats to low dose DBP determines epigenetic alterations of programming of sex brain differentiation and regulation of testicular steroidogenesis that leads to reproductive disorders and accelerated aging of reproductive system.

Keywords: Aging; Dibutylphthalate; Male rats; Prenatal effect; Sexual behavior; Testosterone.

Fig. 1

Average indices of sexual behavior for homosexual and female types in male rats aged 10 months after prenatal administration of DBP. Notes: five rats in each group. Before testing, males were orchidectomized and primed with estradiol and progesterone (see text for details). The test lasted 10 min or up to 10 mounts of the active male. Left bars—controls, right bars—DBP. a The number of mounts of the experimental males on the active normal male, b the number of males with homosexual behavior, c the number of males with lordosis responses. Statistical analysis by Wilcoxon–Mann–Whitney non-parametric U-criterion for group A and by the sign test for groups B and C. *p < 0.05 compared with control

Fig. 2

Average indices of homosexual behavior in male rats aged 18 months after prenatal administration of DBP. Notes: five rats in each group. Before testing, males were orchidectomized and primed with estradiol and progesterone (see text for details). The test lasted 10 min. Left bars—controls, right bars—DBP. a The number of mounts of the experimental males on the active normal male, b the number of males with homosexual behavior. Statistical analysis by Wilcoxon–Mann–Whitney non-parametric U-criterion for a and by the sign test for b. *p < 0.05 compared with the control