Transcript The Effects of Nitroglycerin on the Heart Rate of the 120

The Effects of Nitroglycerin on the
Heart Rate of the 120-hour in vivo and
in vitro Chicken Embryo
Adrienne Dorward, Susan Mette,
Jacqueline McLaughlin, Ph.D.
The Pennsylvania State University,
Berks-Lehigh Valley College
Introduction
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The development of the embryonic chicken
heart begins with a series of cellular
migrations, fusions, and specific
differentiations.
The heart develops from the fusion of a pair
of precardiac mesodermal tubes that give rise
to four regions located anterior to posterior:
bulbus cordis, ventricle, atrium, and sinus
venosus (McLaughlin and McCain, 1999).
The 120-hour chicken embryo heart develops
into 4 chambers: left and right atria, and left
and right ventricles; at this time the sinus
venosus has become the mature pacemaker
or the SA node, which regulates the electrical
signals that cause muscle contractions in the
embryonic heart.
http://www.lv.psu.edu/jxm57/chicklab/outline.html#introduction
Background
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Nitroglycerin (NG) is a common cardiac drug used
to treat angina pectoris, and is also administered
to prevent a myocardial infarction; this drug lowers
blood pressure.
It is well known that NG relaxes vascular smooth
muscle, venous more than arterial.
Figure 1A: Chemical
Structure of NG
C 3H 5N 3O9
Diagram from www.chemfinder.cambridgesoft.com
Background
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The dilation of venous smooth muscle promotes
peripheral pooling of blood, which results in a lower
venous return, and the amount of blood that the
heart has to pump results in a decreased left
ventricular end-diastolic pressure. This decreases
the workload on the heart and the amount of
oxygen as well (Physicians’ Desk Reference,
2001).
Background
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When NG is administered in the body, enzymes
within the cell convert it to the gas, nitrous oxide
(NO).
NO then functions as a hormone by stimulating an
enzyme in the plasma membrane, which creates a
second messenger.
The second messenger relaxes nearby smooth
muscle, which allows the blood vessels to dilate.
In the heart, the dilation of the coronary vessels
occurs.
(Campbell, 2002).
Purpose
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We investigated the effects of Nitroglycerin (NG) on
the in vivo and in vitro 120-hour embryonic chicken
heart rate before and after exposure to 0.008%,
0.08%, and 0.8% NG concentrations.
In a side study, we explored the effects of adding a
0.02% alcohol (Etoh) solution, a known vasodilator
and depressant, after administering the 0.8%
concentration of NG in both the in vivo and in vitro
embryos.
Purpose
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We hypothesized that exposure to NG would cause
bradycardia on both the in vivo and in vitro heart
rates, directly proportional to the NG concentration,
due to vasodilation of the coronary vessels and
increase in cardiac output.
The addition of Etoh would enhance the effects of
NG by further inducing bradycardia, leading to
fibrillation and cardiac arrest because both are
known vasodilators.
Methods
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Prepared NG concentrations of 0.8%,
0.08%, and 0.008% from an 80% NG
liquid stock and chick saline.
An Etoh concentration of 0.02% was
available for use.
Obtained four, 120-hour chicken
embryos/eggs.
Employed Cruz’s (1993) “window”
method.
Determined in vivo heart rate for 15
seconds (5 times) for each.
Added 2 drops of a separate
concentration of NG to each embryo.
Determined subsequent heart rates.
Added Etoh to embryo #4.
Determined its heart rate.
Methods
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Obtained three, 120-hour chicken
embryos/eggs.
Windowed the eggs using Cruz’s (1993)
“window” method.
Explanted the embryos using Cruz’s (1993)
“explantation” method.
Determined in vitro heart rate for each.
Added 2 drops of a separate concentration
of NG to each embryo.
Determined subsequent heart rates for
each.
Added Etoh to embryo # 3.
Determined heart rate.
Data Interpretation
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In all trials, a decrease in heart rate was noted after the specific NG
concentrations were added for both in vivo and in vitro.
A decrease in heart rate was noted after adding the Etoh in the in
vivo embryo, but the heart rate increased in the in vitro embryo.
Periods of bradycardia, fibrillation, tachycardia, and other
arrhythmias were noted with all trials, except the 0.008% NG
concentrations.
Results
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The average heart rate
for chick embryo #1 in
vivo was 138 bpm.
The average heart rate
after adding 0.008%
NG was 96 bpm.
The heart rate
decreased by 42 bpm
after NG was added.
Figure #1
Average In Vivo Heart Rates
160
140
120
Beats per minute
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100
80
60
40
20
0
Control
0.008%NG
Concentration
Results
Figure #2
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The average heart rate
for chick embryo #2 in
vivo was 134 bpm.
The average heart rate
after adding 0.08% NG
was 117 bpm.
The heart rate
decreased by 17 bpm
after NG was added.
Average In Vivo Heart Rates
140
135
beats per minute
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130
125
120
115
110
105
Control
0.08%NG
Concentration
Results
Figure #3
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The average heart
rate for chick embryo
#3 in vivo was 146
bpm.
The average heart
rate after adding 0.8%
NG was 120 bpm.
The heart rate
decreased by 26 bpm
after NG was added.
Average In Vivo Heart Rates
160
140
beats per minute

120
100
80
60
40
20
0
Control
0.8%NG
Concentration
Results
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The average heart rate
for chick embryo #4 in
vivo was 105 bpm.
The average heart rate
after adding 0.8% NG
and 0.02% Etoh was
53 bpm.
The heart rate
decreased by 52 bpm
after both NG and Etoh
were added.
Figure #4
Average In Vivo Heart Rates
120
100
beats per minute

80
60
40
20
0
Control
0.8%NG&0.02%Etoh
Concentration
Results
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The average heart rate
for in vitro chick embryo
#1 was 106 bpm.
The average heart rate
after adding 0.008% NG
was 90 bpm.
The heart rate decreased
by 16 bpm after adding
the NG.
Figure #5
Average In Vitro Heart Rates
110
105
beats per minute
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100
95
90
85
80
Control
0.008%NG
Concentrations
Results
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The average in vitro
heart rate for chick
embryo #2 was 64
bpm.
The average heart rate
after adding 0.08% NG
was 36 bpm.
The heart rate
decreased by 28 bpm
after adding the NG.
Figure #6
Average In Vitro Heart Rates
70
60
beats per minute
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50
40
30
20
10
0
Control
0.08%NG
Concentration
Results
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The average in vitro heart
rate for chick embryo #3 was
89 bpm.
The average heart rate after
adding 0.8% NG was 58
bpm.
The average heart rate after
adding 0.8% NG and 0.02%
Etoh was 84 bpm.
The heart rate decreased by
31 bpm after adding the NG,
but increased 26 bpm after
adding the Etoh.
Figure #7
Average In Vitro Heart Rates
100
90
80
beats per minute
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70
60
50
40
30
20
10
0
Control
0.8%NG
Concentration
0.08%NG & 0.02%Etoh
Conclusion
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Bradycardia did occur for all concentrations of NG in
both the in vivo and in vitro embryos, which supports
our hypothesis.
The heart rate of the in vitro embryo decreased in
direct proportion to the increase in NG concentration,
but did not in the in vivo embryo.
The discrepancy may be due to the irregularities in
heart rate, such as fibrillation and other arrhythmias
that were noted with the greater concentrations.
Conclusion
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The side study of adding 0.002% Etoh after the
administration of the 0.8% NG solution produced
mixed results.
The heart rate of the in vivo embryo decreased
significantly, however, the in vitro heart rate
increased, but was still lower than the control.
This increase may be due to the observed constant
fibrillation that occurred after the administration of
Etoh, which also supports our hypothesis.
Conclusion
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Overall, NG proved to be a vasodilator and
decreased HR.
The findings in this experiment correlate with the
known effects that this drug has on the human heart.
NG indirectly creates a secondary messenger that
causes the dilation of coronary vessels. This
vasodilation decreases the workload on the heart,
lowers blood pressure, and ultimately results in a
lower heart rate.
In all trials, the heart muscles were relaxed at some
point.
Future Experiments
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Use lower concentrations of NG to see if bradycardia
will still occur.
Use higher concentrations of NG to test if too much
will induce cardiac arrest.
Administer the Etoh before the NG to see if NG will
increase the effects of Etoh for a side study.
Use caffeine, a known stimulant, instead of Etoh to
see if the caffeine would reverse the effects of the
NG for a side study.
References
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McLaughlin, J.S. and McCain, E.R. “Development and
physiological aspects of the chicken embryonic heart”.
1999. http://www.lv.psu.edu/jxm57/chicklab/(12 Feb.
2003).
Physicians’ Desk Reference (55th ed.). 2001. Public Medical
Economics Co., Montvale, New Jersey,1604 pages.
[ISBN 1-56363- 375-2] [book].
Campbell, N.A. and Reece, J.B. Biology (6th ed.). 2002.
Benjamin Cummings, New York, 1038 pages. [ISBN 08053-6624-5] [book].