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The Effect of
Caffeine on the Heart Rates of Three-Day Old Chick
Embryos
Catherine Crawford,
Swarthmore College, Class of 2007
Joyce Park, Franklin and Marshall College, Class of 2002
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Objective
The
purpose of this experiment is to observe the effect of
caffeine on the heart rate of three day old chick embryos by
directly treating them with five different concentrations of
caffeine.
Introduction
The
first functional organ of chick embryos is the heart
(Gilbert, 2003). 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.
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These
signals depend on a sodium-calcium gradient
(created by a Na+-Ca++ exchange pump) and calcium
channels (Bellairs, R. and Osmond, M. 1998).
Nevertheless, 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
increases the teratogenic effects of ephedrine on
embryonic chick hearts (Nishikawa, 1985). Although
it is not known exactly how caffeine effects an
embryo on a molecular level, embryos have not yet
developed the succession of liver enzymes present
in adults that are needed to degrade caffeine
(Braun, 1996).
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Figure 1. A three-day-old chick
embryo, with visible circulatory system and
somites.
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However, previous studies have
shown that, in addition to inducing cardiovascular mutations
in embryonic chicks, caffeine also has immediate effects on
the embryo. Exposure to increasing levels of caffeine
increase heart rates, decrease the forcefulness of each
contraction, and at higher levels of caffeine, so much that
the hearts stop beating. The purpose of this study was to
examine the effects of five different concentrations of
caffeine 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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