Hormone replacement therapy refers to any form of hormone therapy wherein the patient, in the course of medical treatment, receives hormones, either to supplement a lack of naturally occurring hormones, or to substitute other hormones for naturally occurring hormones. Common forms of hormone replacement therapy include:
Rodent Studies for HRT
Many studies on the effects of Hormone Replacement Therapy (HRT) have been conducted on rats. Predominantly, these studies have looked at the effects of estradiol, a type of estrogen, on rats’ performances on various tasks. Often, the rodents will be ovariectomized, meaning they have their ovaries removed. This prevents the production and release of estrogen and progesterone, and mimics the occurrence of menopause in human females. Once the ovaries have been removed, researchers will administer estrogen, progesterone, or both to see what the effects are on the rats’ behaviors. Rats are good animal models because they have similar cognitive deficits to humans as they age, and administering hormone therapy to them is easy.[2]
Overall, the results of these studies are non-conclusive. Some studies find impairments due to the HRT, where others find improvements. A common theme that runs through many studies is that rats that are given HRT perform better on tasks activating thehippocampus, and worse on tasks involving the prefrontal cortex. For example, Wang et al (2009) found that ovariectomized rats that were exposed to estradiol did considerably worse than rats who were not exposed to estradiol, on a delayed spatial reasoning task – a task that activates the prefrontal cortex.[3] Another study that looked at the effects of estradiol in ovariectomized rats, found that when HRT was administered immediately following the removal of the ovaries, there was a decrease in anxious and depressive behaviors, while also improvement on cognitive performance on an object-placement task (though this was a hippocampal-based task).[4] Hence, the timing of the hormone replacement therapy and the activated brain regions are significant factors in assessing effectiveness of HRT. Another important aspect is whether or not the treatment is chronic or cyclic. Chronic treatment is daily doses of the hormone, while cyclic treatment is based on the normal cycling patterns of that hormone. One study found that the group of rodents, who received estradiol and a type of progesterone chronically, performed the worst on the maze task; whereas, the group who received only estradiol cyclically showed some improvements.[5]
More research in this area is needed. Some important results can be gathered from these rodent studies though. First, that differing brain regions may respond in a variety of ways to HRT. Second, that the timing of the therapy is integral to the chances of success. Third, that how the hormones are administered, either chronically or cyclically, may make an important difference in their effectiveness.
Effects on Women
As recently as 2005 women have had a positive attitude towards hormone replacement therapy but based on the empirical data these attitudes may be overly optimistic.[6] Currently, however, most women do not find HRT to be an effective solution. There is still much to learn about how HRT affects people. Below we talk about a few of the positive and negative effects of HRT. Generally, HRT is initially helpful but if used for a long period of time it loses its effectiveness. On the other hand, there are times when HRT is not only ineffective but actually detrimental to people.
Hormone replacement therapy is not always good. An example of this is in a study where women going through menopause using HRT with Progestin as a major component of the therapy show a few negative effects on hearing. Not only does the Progestin decrease the functionality of many regions of the ear it also reduces the effectiveness in parts of the central nervous system used for hearing.[7] Also in some situations it has been shown that menopausal women who are caregivers and receive HRT can have an increased chance for cardiovascular issues. As caregivers it is implied that they have more acute stress in their lives and that acute stress along with the HRT is priming negative cardiovascular effects.[8]
Hormone replacement therapy can have beneficial effects. In a study women taking estrogen through HRT showed that the estrogen positively affects the prefrontal cortex by boosting the working memory. This suggests that estrogen may play a key role in certain frontal lobe functions in women.[9] Women using HRT after menopause have no additional weight gain compared to women who do not use HRT.[10] Also women who use HRT with an estrogen component show positive effects in their sex life (mainly increasing their sex drive and sexual sensitivity) but the effects are inconsistent across women. Sadly, these sexual improvements can dissipate after receiving HRT for extended periods of time.[11]