Re: How does Paracetamol affect heart rate in daphnia?

Hello Farheen! Thank you for your question.

You asked: "I am doing a project on the effects on drugs on the heart rate of Daphnia. I have searched high and low but nobody seems to have done any research on the effects of paracetamol on their heart rate. I need to know if it would increase or decrease it as my results show a decrease, but I have no idea if this is the correct response! ANY information would be gratefully received."

First off, congratulations on your research project! Very often, researchers perform their experiments with a hypothesis in mind, only to find out that their results are completely the opposite. This is OK!!! That's why what we do is called "research." We are investigating something that needs to be investigated because we don't know the answer yet! Conflicting results occur all the time in science, and this is good! It causes people to rethink their methods, their data analyses techniques, their hypotheses... and attempt to dig further to answer these new questions. Why spend time, money, and brain cells on tackling a scientific hypothesis if you already know that there is a "correct" answer?? :)

OK. On to your question.

Paracetamol, also known as acetaminophen (or most commonly, Tylenol), is a drug used to relive pain associated with headaches and muscle aches. You get results comparable to those of aspirin, although their mechanisms of action are different. While both paracetamol and aspirin block the production of prostaglandins (chemicals involved in pain transmission), aspirin blocks the production at the site of the pain, while paracetamol appears to block these chemicals in the brain.

Off the top of my head, I cannot think of any interactions that paracetamol could directly have on heart rate. The great thing about these types of over-the-counter pain-relief medications is that they really are very safe if taken at the doses recommended by their doctor. There are little side effects, and these are most often associated with overdosing --- people will usually develop liver and kidney failure as a result.

I did some literature searches for you, and found some information which linked paracetamol use to asthma (in the journal Thorax, 2000;55:266-70). Paracetamol is metabolized in the liver. The liver relies on a molecule called glutathione to help process paracetamol as it biotransforms. Glutathione, though, is an important biological antioxidant which helps to destroy reactive oxygen intermediates associated with inflammation. People with asthma are basically having an inflammatory reaction in their lungs, and if they've been taking paracetamol for a while, they might not have enough glutathione to help keep the inflammation down.

I could not find any direct associations between paracetamol and heart rate. I say "direct", though, because the cardiovascular system is finely balanced with the other organ systems in the body. Therefore, alterations in, say, liver function, can ultimately affect the heart. These would be considered secondary, or indirect, effects. Let's theorize on how the heart rate could change "as a result" of other things going on.

We know that overdosing on paracetamol can lead to liver and kidney failure. A dysfunction liver and kidney would not process the molecules they're supposed to do properly. This could lead to accumulations of toxic intermediate molecules that should really be biotransformed by the liver or excreted in the urine by the kidneys. Terrific, now these toxins are building up in the dysfunctional kidneys and liver and circulating in the blood. Chemical imbalances in the blood due to the addition of these intermediates (including changes in potassium, sodium, magnesium, calcium, chloride levels...), changes in the ion gradients, changes in blood pH... all could theoretically lead to cardiac arrhythmias (irregular heart beats). In addition, the stress the body would most likely undergo during liver and kidney failure (including pain, nausea, abdominal tenderness…) could trigger a sympathetic response by the body --- this leads to the release of epinephrine (adrenaline), which increases heart rate.

I'm afraid I don't know why your Daphnia experienced a decrease in heart rate with paracetamol. Even if you are overdosing your Daphnia, I would think that the stress and secondary effects (like I mentioned above) would lead to an increase in heart rate. Hmmm... OH WAIT ---- is the paracetamol you're using pure, or is it in combination with CODEINE? If your paracetamol contains codeine, this would explain the decrease in heart rate that you are seeing! Codeine depresses the sympathetic response of the body, decreasing the heart rate through vagal mediation (branches of the vagus nerves innervate the heart). In addition, codeine has a direct effect on the conduction nodes (both the SA and AV nodes) in the heart that are responsible for heart rate, slowing the conduction of cardiac impulses and ultimately leading to a decreased heart rate. Codeine is often added to pain-relief medications such as paracetamol to calm the person during their pain --- sort of an anesthetic effect.

Hope my answer was of some help. Please feel free to submit another question to MadSci if you have further questions.

Sincerely,

G. Monreal Check here, here, and here for more information.