ethinylestradiol & levonorgestrel
This combination of medicines is an oral contraceptive. You probably know of this medicine as 'the pill' and it is important for family planning allowing you to decide when you have children.
But it also has many other uses!
It can be used to clear up acne, reduce pain and control bleeding associated with menstruation and regulate menstrual cycles.
How does it work?
Hormones are chemicals found naturally in our body that are used to send messages from one part of the body to another. They travel in the blood stream and are known as signalling molecules.
Hormones that have the core 4-ring system (shown to the right) within their chemical structure are called steroid hormones. They regulate our metabolism, immune system, inflammation, sexual characteristics and even the salt and water balance in our cells. Recall that steroid hormones are able to cross cell membranes passively (through diffusion).
Steroid hormones are fat soluble, so they are able to diffuse across a cell membrane. They bind with receptors inside the cell membrane.
There are a range of steroid hormones found in the human body, for example oestradiol and progesterone. These hormones are part of the natural regulation of the menstrual cycle. If you look at the diagram on the left, you can see that there is a range of hormones involved in the menstrual cycle. A peak in oestradiol levels is involved in the maturation and release of an ovum (it causes increased levels of lutenising hormone and follicle stimulating hormone, which stimulate ovulation). Progesterone is released later in the cycle, and is involved in the thickening of the endometrial lining. A drop in progesterone levels causes menstruation.
Both of these hormones are made in the ovaries.
The medicines used in the contraceptive pill are very similar to oestradiol and progesterone. Ethinylestradiol is an analogue of oestradiol, and levonorgestrel is an analogue of progesterone. This means that they have very similar chemical structures.
Analogues mimic the natural compounds they are analogues of by behaving in similar ways within the body. Thus ethinylestradiol and levonorgestrel influence the function of the female reproductive system in the same way that estradiol and progesterone do. Consistent levels of ethinylestradiol prevents the mid-cycle increase in lutenising hormone and follicle stimulating hormone, thus preventing ovulation. If the body has high levels of progesterone, the production of lutenising hormone and follicle stimulating hormone is suppressed, thus also preventing ovulation.
Other effects of the combined pill include thickening of vaginal fluids and prevention of implantation of fertilised ova.
Can you identify the similarities and differences between the chemical structures of ethinylestradiol, estradiol, levonorgestrel and progesterone shown below?
ethinylest-radiol
Estradiol
levonorge-strel
progesterone
These hormones are involved in a wide range of systems in the body as well as reproduction, for example mood, appetite and water retention. There is a lot more to be learned about these medicines.
Did you know: Oral contraceptives are not effective protection against sexually transmitted infections.