Scientists developed the medicine salbutamol to treat asthma. They created a molecule that is similar to adrenaline - a natural bronchodilator produced by the body. Let's see how it works.
Picture 13. Adrenaline is like a key that fits into the lock of the receptor making the muscles relax.
Asthma and bronchodilation
During an asthma attack, the bronchioles that feed air deep into the lungs become inflamed and narrowed. This is due to muscles in their walls contracting. The reduction in air flow can be life-threatening if it is not treated with a bronchodilator.
The body has a natural hormone that will help to alleviate the symptoms of an asthma attack. It is adrenaline. Adrenaline has a specific shape and fits into active sites on the cells in the muscle walls. When it attaches itself to these active sites, it makes the muscles relax. This relaxation causes the airways to open up - or dilate. This process is called bronchodilation.
The effect of adrenaline was the starting point for the research that eventually led to the development of modern bronchodilators like salbutamol (also known as Ventolin™) that are found in inhalers.
Picture 14. The hormone adrenaline acts as a natural bronchodilator. Unfortunately it has unwanted side effects.
The development of salbutamol
Adrenaline is a complex hormone. It can act as a natural bronchodilator but it also causes some unwanted side effects. These include an increase in the heart rate and blood pressure. Research chemists added an extra chemical group to try and stop some of its unwanted side effects.
Picture 14 shows the structure of adrenaline. To see how it triggers bronchodilation, we need to think of the shape of the molecule. Researchers chemically modified adrenaline to find molecules that would have the same effect in dilating the bronchioles but without the stimulation of the heart.
The first molecule that they synthesised was called isoprenaline. It did cause bronchodilation but was very quickly broken down by enzymes in the body. This meant that it was not active enough in the body to be a useful treatment for asthma.
The research chemists looked for another modification to the molecule that would stop it from being inactivated but still retain its ability to cause bronchodilation.
Finally, they produced the molecule that they wanted. It had a similar shape to adrenaline which made it a good bronchodilator and it worked well when inhaled. However, its extra structure limited its side effects. They called it salbutamol. It is also known by its trade name of Ventolin™ and has been a successful treatment for asthma since 1968.
How bronchodilators work?
Salbutamol (Ventolin™) was the first really successful bronchodilator and is still used widely today. Taken using an inhaler, the medicine causes the muscles in the wall of the bronchioles to relax. In turn, this leads to the airways opening up, or dilating. These medicines are called bronchodilators.
Research chemists at developed a molecule that would fit into adrenaline receptors on the muscles in the bronchiole walls.
Adrenaline could not be used as it causes many unwanted side effects. Salbutamol is a similar shape to adrenaline but causes bronchodilation without unacceptable side effects.
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