Effects of neonatal 17-ethinyloestradiol exposure on female-paced mating behaviour in the rat

Correct perinatal oestrogen levels are critical for sexual differentiation. For example, perinatal exposure to oestrogen causes masculinization and defeminization of the brain in female rats and also induces delayed effects after maturation characterized by early onset of abnormal oestrus cycling. However, the mechanisms underlying the above effects of oestrogen remain to be fully determined. 17-ethinyloestradiol (EE), a common synthetic oestrogen widely used in oral contraceptives, binds specifically to oestrogen receptors. In this study, we demonstrated the effects of a single neonatal injection of high- or low-dose EE on reproductive behaviours. Female rats within 24h after birth were subcutaneously injected with sesame oil, EE (0.02, 2mg kg(-1)) and 17-oestradiol (E-2) (20mg kg(-1)). Between 11 and 15weeks of age, sexual behaviour was tested twice in a paced mating situation. Latency to enter, lordosis and soliciting behaviour were recorded. Both high-dose EE- and E-2-treated females showed a significantly lower lordosis quotient, decreased soliciting behaviours, increased rejection and fighting numbers. Accessibility to males was also delayed by neonatal E-2 exposure, although it was shortened by high-dose EE exposure. In contrast, low-dose EE-treated females did not exhibit impaired sexual behaviour. These results suggest that single neonatal exposure to a high dose of EE or E-2 disturbs the normal development of the female brain, resulting in impaired sexual behaviours in a female-paced mating situation. Besides, the differences noted between high-dose EE- and E-2-treated females might be caused by different affinities of the oestrogen receptors, metabolic rates or mechanisms of action. Copyright (c) 2017 John Wiley & Sons, Ltd. Perinatal exposure to xeno-oestrogens can disrupt female sexual development, leading to changes in reproductive behaviour in adulthood, but the effects remain to be fully determined. We examined the effects of a single perinatal exposure to low (0.02mg kg(-1)) and high (2.0mg kg(-1)) doses of 17-ethinyloestradiol (EE) on female rats in a paced mating test. The high EE dose, but not the low dose, disrupted females' sexual behaviours in adulthood. Such exposure could pose a risk to reproductive health.