Re: How does nicotine affect the heart rate of Daphnia?

Hello Christine,

Thank you for your interesting question.  I apologise for taking so long to 
answer your question.  I have not investigated the effect of nicotine on 
daphnia heart rate myself and I despite a thorough search of the literature 
database I have been unable to find anywhere describing what this effect 
is.  I can tell you how nicotine affects human heart rate and the 
mechanisms by which this occurs, and if you get the same result in daphnia 
then nicotine may be working on a similar system, although you should be 
very cautious about making comparisons between the two due to considerable 
differences between humans and daphnia there may not be the same systems 
regulating the rate of contraction of human and daphnia hearts.

Many drugs and chemicals work in the body by either mimicking or blocking 
the effects of the natural chemicals in the body.  Additionally they may 
stimulate or block the release of a chemical from the body.  Nicotine has 
many different effects in the body, but usually one effect dominates giving 
the overall observed response.

In humans, and in all mammals as far as I know, nicotine increases the 
heart rate.  This is because nicotine stimulates the release of adrenalin 
and noradrenalin, a chemical very similar to adrenalin.  Collectively these 
chemicals are termed catecholamines.   The fact that nicotine is working 
via this pathway can be demonstrated by drugs that block catecholamine 
receptors, for example b-blockers, which you may have heard about.  These 
drugs block the effect of nicotine increasing heart rate.  Nicotine causes 
a slight increase in the concentrations of adrenalin in the blood.  However 
an injection of adrenalin that gives the same increase in blood 
concentrations as seen with nicotine does not increase the heart rate as 
much as is observed with nicotine.  Therefore the nicotine must be having 
more localised effects and it is assumed that it stimulates the local 
release of catecholamines in the heart from local nerve terminals.

I hope that his information is of some use to you.

Good luck with your experiment

David Burton