When we think of hormones, we tend to think of hormones as having specific effects. Ovarian hormones are involved in breast development; androgens increase muscle mass; oxytocin is somehow involved in social behaviors; insulin does something to blood sugar. There are a number of points to be made.If it’s not obvious, hormones influence behaviors in large part by acting on our brains. Perhaps because of interest in oxytocin, more and more, people are realizing this.
It is very important to understand two other concepts. When we talk about “estrogen,” different people can mean different things. To an endocrinologist like me, it refers to a class of hormones (estrogens), which includes very specific hormones, like estradiol (that is, estradiol is an estrogen, but it is not correct to refer to estradiol as “estrogen”). To others, it refers to the “cocktail” of many estrogens present in some estrogen replacements, like Premarin, a compound drug that contains many estrogens. And yet to others, estrogen may refer to the compounds present in some plants that have some of the properties of estradiol.There are many estrogens, and estradiol, the hormone secreted by the ovaries in women and other animals is not the same thing as Premarin.
Something else to keep in mind is that the effects of hormones are never simple. To take the effects of estradiol on reproductive behavior in rodents, a useful model that can tell us a lot about how hormones act in the brains of humans – estradiol and progesterone can have very different effects depending on the manner that the animal is treated. We have learned a great deal from work in rodents. For example, two very small doses of estradiol can have different effects than one large dose. Furthermore, hormones interact with each other in very complex ways; for example, progesterone can either inhibit, facilitate, or have no effect on the expression of behavior, depending on dose and time that it is administered relative to estradiol. Although there are species differences in precisely what hormones do to an animal, there is much that we have learned from working with rodents that can inform us of issues to consider when thinking about women.