Reproductive impacts of excreted and environmental estrogens, and natural steroid transfer between individuals

点击翻译按钮获取中文摘要

Steroid hormones such as estrogens are normally understood to act only within the body that produces them. This lab has been collecting evidence that steroids can also pass between individuals, being excreted by one individual and then absorbed by others. We are studying this in lab mice; however this research should be relevant to many species because steroid dynamics are very similar across mammals. The urine of male mice contains high levels of estradiol, the most powerful estrogen. Males emit more estradiol when they are near females. This is associated with two well-known pheromonal effects: 1) advancement of the age of puberty in juvenile females, and 2) disruption of early pregnancy in females inseminated by another male. Both of these phenomena can be mimicked by giving females very small amounts of estrogens, which produce these effects by acting on receptors in the uterus and possibly also in the brain. We think that the estradiol in males' urine may simply be getting into females' bodies. In order to prove this, we are tracing radiolabelled (3H) estradiol from males' circulation through their urine into nearby females' circulation and to receptors in the uterus. We will also look at 3H-estradiol uptake in the hypothalamus of the brain, where estrogens control female sexual behaviour. Our work on the pheromonal effects of excreted estrogens needs to be reconciled with some older theories about the chemistry of mammalian pheromones. We will compare the impacts of estrogens with chemicals that have been suggested by other researchers. We will also investigate other sources of estrogens from outside the body, including phytoestrogens found in plant-based foods and manmade environmental contaminants such as bisphenol-A (BPA) from some plastics, as these can act on the same mechanisms as do excreted estrogens. We will study how these different sources of estrogens might interact to influence the age of female puberty and the outcome of early pregnancy. This research could transform understanding of the chemical nature of mammalian pheromones, while providing insights into the chemical factors that influence the age of female puberty and determine the success or failure of early pregnancy.