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How Do Anabolic Steroids Work?

Instructor: Amanda Robb
In this lesson we'll explain the mechanism of action of anabolic steroids. We'll go over how they alter your cells to cause changes like increased muscle growth, and some of the main reasons people turn to steroids.

What Are Anabolic Steroids?

As you enter the gym to get your morning workout in, there is the typical gang of guys, lifting weights you'd need a small forklift for, with muscles exploding out of their tank tops. Although many men and women achieve this athletic prowess with simply hard work and dedication, some are tempted to take the easy way out with anabolic steroids.

Anabolic steroids are man made chemicals that act like the sex hormone testosterone. Although both men and women make testosterone, men make it in much larger quantities, so it is considered a male hormone and usually has masculinizing effects in women who use steroids.

So how anabolic steroids work to produce the muscle building effects they are so famous for, as well as the side effects?

General Mechanism of Action

Anabolic steroids are tiny molecules made of carbon atoms arranged in a ring. Their size and atomic composition allows them to easily enter cells and get into the brain of the cell, called the nucleus. There, they tell the cell to make different proteins through attaching to small molecules called receptors. When the anabolic steroid attaches, or binds to, the receptor, the cell knows its time to change what proteins it's making.

It's like a megaphone for the anabolic steroid, shouting the message to the cell to change proteins. DNA is the instructions for protein in the cell, so the receptors testosterone attaches to are near the DNA in the nucleus.

Mechanism of action of testosterone
testosterone signaling

Proteins aren't just important in your diet to build muscle! All of your cells make protein, and they are essential for all structure and function. Anabolic steroids change the amount of a type of protein made. It would be like working in a sewing factory and then hiring 10 new seamstresses and two tailors just to make shirts. Your output of shirts would increase drastically. Steroids do the same thing to cells.

Muscular System

Anabolic steroids need to bind to receptors in skeletal muscle, the muscle in our arms and legs we use for lifting, to cause the changes in protein production. In muscle cells, anabolic steroids enter the nucleus and change how much of certain proteins are made. Proteins that are involved in building muscle are upregulated, meaning the steroids 'up' the number of them being made. Proteins that are involved in breaking down muscle are downregulated, meaning less of them are made.

Anabolic steroids increase growth of the muscular system
muscular system

Cortisol is a hormone that causes muscle breakdown, which also binds to receptors. If anabolic steroids outcompete the cortisol, muscle breakdown is prevented, and the body makes more and more cortisol. It thinks, 'Why is this not working? I'll make some more to try to fix the problem.' The elevated levels of cortisol cause problems in the body, like a decreased immune response.

Testosterone displaces cortisol causing the body to make more and more cortisol
cortisol and testosterone

The reverse process happens with testosterone. Since anabolic steroids act like testosterone, the body thinks, 'Hey, I have enough testosterone, let's stop making it all together.' When the person stops taking anabolic steroids, there are extremely low levels of natural testosterone in the body. This causes intense rebound effects, like drastic loss of muscle and feminization. This brings us to the effects on the reproductive system of testosterone. Let's look at that mechanism of action next.

Reproductive System

Testosterone is a sex hormone and regulates the male and female reproductive system, such as sperm and egg production, and the development of breasts and testicles. Testosterone prevents the production of luteinizing hormone (LH) and follicle-stimulating hormone (FSH). These hormones are needed for sperm maturation.

So, when men use anabolic steroids, LH an FSH go down, so there are less sperm made, which can lead to infertility. Decreased levels of LH and FSH also lead to testicular atrophy, or a shrinking of the testicles. The muscles get bigger, but unfortunately the opposite is true for the male genitalia.

Excess testosterone is converted to estrogen, a female hormone in the body. So, when men take large quantities of testosterone, they raise their estrogen levels. This causes a feminizing effect, where males develop breast tissue, decreased sex drive, decreased testicle size, and decreased sperm production.

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