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		The Effect of Caffeine on the Heart Rates of Chick Embryos Ruth Simeon and Nick Scarpill, Millersville University Catherine Crawford, Swarthmore College, Class of 2007 Joyce Park, Franklin and Marshall College, Class of 2002
		Objective       The purpose of this experiment is to observe the effect of caffeine on the heart rate of three day old chick embryos. Isolated embryonic chick hearts will be incubated in solutions containing caffeine at concentrations between 0.1 mg/ml and 1 mg/ml, and their heart rates measured over 1 minute time intervals. Introduction       The first functional organ of chick embryos is the heart. At three days, chick embryos already have a tubular heart structure with one atrium and one ventricle, (Gilbert, 2003). As the circulatory system is the first to develop, the heart does not rely on external innervations to initiate contractions. Heart muscle cells are intrinsically rhythmic and pulsate in unison by releasing electrical signals.  These signals depend on a sodium-calcium gradient (created by a Na+-Ca++ exchange pump) and calcium channels (Bellairs and Osmond, 1998). In addition, other signaling molecules, such as acetylcholine and norinephrine can affect embryonic hearts (Gilbert, 2003). Due to the importance of the circulatory system, morphological changes caused by signals and external chemicals, such as caffeine, have the potential to cause irreversible harm on a developing embryo. Caffeine is a trimethylxanthine (Gwinn, 1992) and a teratogen, which is an agent responsible for developmental abnormalities (Braun, 1996). Caffeine also increases the teratogenic effects of ephedrine on embryonic chick hearts (Nishikawa, 1985). Although it is not known exactly how caffeine affects an embryo on a molecular level, they have not yet developed the succession of liver enzymes present in adults that are needed to degrade caffeine (Braun, 1996).   Figure 1. A three-day-old chick embryo, with visible circulatory system and somites. Figure 2. A four-day chick embryo.     Previous studies have shown that caffeine increases the force of contraction of the heart in fetal humans, causing irregular heartbeats (Spiller, 1998). Exposure to increasing levels of caffeine increases the heart rate and decreases the forcefulness of each contraction. The purpose of this study was to examine the effects of five different concentrations of caffeine (ranging from 0.1 mg/ml to 1 mg/ml) on the heart rates of embryonic chicks that were three days old. It was expected that the increase in heart rates would be proportional to the concentration of caffeine to which the heart was exposed.

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