|MadSci Network: General Biology|
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
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