Sex hormones: How do they work?

03 August 2015

Interview with

Dr Helen Simpson, Addenbrooke's University

Hormones are the chemical messengers that control eating, sleeping, mood, and also Male and femalehold the key to our sex lives. How do hormones work, and what happens when you start taking sex hormone replacements? Dr Helen Simpson is a consultant hormone specialist from Addenbrooke's hospital, and she covered the basics for Chris Smith...

Helen - So hormones are chemical messengers which are produced by endocrine glands into the bloodstreams. From there, they go to distant sites in the body acting on their target cells. They control pretty much everything that we do. So, they help provide energy for our cells to work. They're controlled in regulating growth and reproduction.

Chris - How do they actually work? So although we're secreting these chemicals from one place in the body to another, how do the target cells know they're being targeted?

Helen - So if you like, it's a little bit like a lock and a key in a door. So, the hormone is the key and they act on receptors which are on all cells of the body and they're the locks and there's a specific configuration for different hormones in their particular receptor. So, if you think about oestrogen - the female reproductive hormone - that's produced from the ovaries and this acts on certain particular cells in the body, so the breast tissues, when we go through to puberty, bones and the uterus.

Chris - You can therefore constrain which tissues respond to your hormone by having the receptor, the docking station, the hormone wants to see expressed on those particular tissues which will give them the ability to see that hormone going around in the bloodstream.

Helen - That's right and then some hormones such as thyroxine - the thyroid hormone and growth hormone, they act on actually all the cells in the body so they have a much more widespread effect. So, it enables the endocrine system to target appropriately.

Chris - What about the reproductive system? What are the key players in the reproductive game?

Helen - So, if we're thinking about reproductive hormones, ovaries produce oestrogen and progesterones and they're the female hormone and testes produce testosterone which is predominantly a male hormone. These act on and are picked up by a negative feedback mechanism from parts of the brain called the hypothalamus and the pituitary. The pituitary gland is a really important gland for endocrinologists because it controls many hormones in the body. It's about the size of a pea and if you get two knitting needles and you put one on top of your nose and one by the ear and they're pressing together where they cross in the middle, that's where the pituitary lives.

Chris - Sounds rather uncomfortable.

Helen - What that can do is regulate and it's a little bit like the accelerator in a car. It tells the ovaries or the testes how much or how little testosterone and oestrogen to make to keep everything in a regular balance.

Chris - People will be associated or familiar with the idea that if you have a drop off in a level of a hormone, any kind of hormone whether that's insulin for diabetes or for thyroid function like thyroxine, we can make these chemicals and put them into the body to replace the missing function?

Helen - That's right, so one of our jobs as endocrinologists is to do blood tests to diagnose if someone has too much or too little of a hormone. So if we're thinking again about the ovaries and if they stop working either at an early age so premature ovarian failure. Or at the average age or menopause at the average age in the fifties, we can do tests to diagnose that and then we can replace the hormones with hormone replacement therapy, predominantly to reduce the symptoms of the oestrogen deficiency. 

Chris - Is it safe?

Helen - It's pretty safe. So 10 years ago, there was a women's health initiative was reported which is a large study from America which had some quite scary data suggesting there was quite a large increase in breast cancer and heart disease. But when this data was reanalysed, it looks like those women were 10 years older than when we use it usually in the UK so over the age of 60. And they were often more overweight than British counterparts. So, when we've looked at the data now, it looks like the increased risk in breast cancer is probably approximately 4 in 1000 women for about five years of use. If you're before the age of the menopause there's no data there saying that these hormones are unsafe.

Chris - And is there an equivalent for men? Could men have a testosterone boost via a patch or whatever to overcome some of their declining testosterone levels with age?

Helen - So testosterone replacement is available in the same way HRT is for women. The controversy is whether this treatment is beneficial for men, of middle-aged men where there's no definite evidence of testosterone deficiency. Again, there does seem to be some risks. The FDA sent out a warning earlier in this year and that there may be increased risks of heart attacks and vascular disease and blood clots in middle-aged men without testosterone deficiency who were using testosterone replacement.

Chris - All of these athletes who are naughty and they abuse anabolic steroids which are male hormones that promote the maleness, they encourage muscle growth and all that kind of thing, do they end up with their bits shrinking because they're basically suppressing strongly the need to make their own testosterone through taking it in a pill?

Helen - That's exactly right. So what happens there is as you're taking a hormone from an exogenous source, the pituitary in the hypothalamus which I mentioned earlier, that essentially goes to sleep. So, it stops sending the signals to the testes and that's partly why they shrink because they're not having to make testosterone anymore. If you take these for enough years then the hypothalamus and pituitary will go to sleep permanently and they won't wake up again.

Chris - So, even if the person stops taking the anabolic steroid then their testes are destined to remain like peanuts forever.

Helen - Essentially, that's right. We're getting more patients referred in this context who then may need to go on medical testosterone replacement.

Chris - It's a sobering message in that, isn't it?

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