вход по аккаунту


Induction of reversal of the heart beat in chick embryos by injection of novocain into the vein.

код для вставкиСкачать
Induction of Reversal of the Heart Beat in Chick
Embryos by Injection of Novocain
into the Vein
Department of Anatomy, Faculty of Medicine and Siriraj Hospital,
University o f Medical Sciences, Bangkok, Thailand
By increasing carbon dioxide in the
chamber occupied by the chick embryo the
metabolic activity of the embryo was modified and reversal of the heart beat could
be produced experimentally (Sangvichien,
'52). From that experiment I came to the
conclusion that for inducing the reversed
heart beat experimentally two factors are
required. One is an increase in percentage
of carbon dioxide in the medium in which
the embryo is suspended, and another is
an intact circulation. The blood in the
vitelline veins which contained a large
percentage of carbon dioxide will flow in
and come in contact with the sino-atrial
part of the heart, suppressing the dominating function of the sino-atrial portion.
This will allow the more cephalically located region in which the metabolic activity had not yet been suppressed to resume
the dominancy as a pace maker. From
that area the wave of contraction would
then spread to other parts of the cardiac
tube. In order to demonstrate that the
sino-atrial portion could be suppressed directly the following experiment has been
performed by using novocain as the depressing agent.
Chick embryos of 42 to 48 hours of incubation were used the same as in the
previous experiment. Fresh eggs were incubated at 100°F. and at the end of the
desired period the shell was opened and
the embryo, together with the vascular
area, cut off from the yolk mass and floated
in warm normal salt solution. The embryo
was then transferred to a cover glass and
fixed there by small slips of filter paper
after the method of Patten and Kramer
( ' 3 3 ) . A few minutes were allowed for the
embryo to recover until the heart beat was
regular and normal. The cover glass with
the embryo was then placed under the dissecting microscope. One per cent novocain
(tinted with very diluted methylene blue
so that the solution could be clearly seen
while passing through the vascular channel) was drawn into a fine glass canula
by sucking with the mouth through a
plastic tube inserted at the other end of
the canula. Air was prevented from entering the canula as it might interfere with
the free flow of the solution. With scissors
the tip of the canula was sharpened by
cutting obliquely, punctured and inserted
into a vein of the vascular area of the
embryo. Usually any branch of the omphalomesenteric veins can serve the purpose, but the one easiest to insert is the
posterior vitelline vein. With gentle blowing the solution could be forced easily into
the circulation of the embryo until it
reached the heart. The amount of the
solution injected was not measured. Before injection with novocain, very dilute
solution of methylene blue in distilled
water was injected to see whether it has
any action on the heart, no effect was detected. Any change then in the chick embryo's heart could be attributed to the
action of novocain.
Twenty-seven embryos nearly identical
in age were used, 18 showed the following
changes. The heart stopped suddenly when
solution of novocain entered the chamber,
and then for about one minute the heart
resumed beating, but contraction started
in regions of the heart other than the
Fig. 1 Photographs showing the configuration of the heart and its relation within the
body at the stage of development utilized i n the experiments. A. At the end of the experiment
to show
where the beats started in embryo after they were stopped by injecting novocain
into the circulation. B. Same embryo after injection with India ink.
sino-atrial region. The place where the
new beat usually started was at the conus,
some at the ventricular region. In one
specimen (no. 1 ) the beat at the conus
continued for nearly 5 minutes without
sign of contraction at the sinus end. The
beat was clearly seen by the appearance
of the approximation of the endothelial
lining for every beat. Contraction in some
embryos lasted less than one minute, and
while contraction still appeared at the
conus, the sinus end resumed beat. This
last type of beat may last as long as 6
minutes before merging into a continuous
wave and the sinus end then resuming
dominancy. Separation of the beats of
contraction were clearly seen by the intervening of the ventricular part which
showed no wave of contraction. The beats
at the two ends were different, in specimen no. 6 the rate at the conus was 20
beats during 25.7 seconds, while at the
sinus end it required only 21 seconds for
20 beats. This difference in rate was not
constant, sometimes the beat at the conus
was more rapid (specimen no. 13).
This experiment confirmed the result
of the previous experiment and that of
Patten and Kramer ( ' 3 3 ) , that the sinus
venosus is not the first part of the heart
to pulsate. As each new part of the heart
is formed, it exhibits a higher intrinsic
rate of contraction than the parts of the
cardiac tube which lie more cephalically
and were previously formed. The sinus
venosus assumes the role of pace-making
in the fully formed heart. If the latter
part of the heart is suppressed either by
the use of carbon dioxide to interfere its
metabolic activity or directly by the injection of novocain into the circulation,
the parts of the heart which are previously
formed will resume the dominancy causing beats to appear in the more cephalic
part of the heart.
Carbon dioxide introduced into the
chamber occupied by the chick embryo
can cause reversal of the heart beat (Sangvichien, '52). In order to demonstrate
that the sino-atrial portion could be suppressed directly 1% novocain tinted with
verv dilute methvlene blue was injected
into the vein of the embryo, The drug
suppressed the sinus end Of the heart
allowing the parts of the heart which are
previously formed to resume dominancy
thus causing reversal of the beat.
Patten, B , M., and T. c.
1933 The initiation of contraction in the embryonic chick
heart. Am. J. Anat., 53: 349-375.
Sangvichien, S. 1952 Experimental reversal of
the heart beat in chick embryos. Anat. Rec.,
112: 529-538.
Без категории
Размер файла
201 Кб
vein, induction, novocain, reversal, injections, beata, embryo, heart, chick
Пожаловаться на содержимое документа