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 S. SANGVICHIEN 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. METHOD 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. RESULTS 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 185 186 S. SANGVICHIEN 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. (4) 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). - CONCLUSION 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. SUMMARY Carbon dioxide introduced into the chamber occupied by the chick embryo NOVOCAIN REVERSAL O F EMBRYO HEART BEAT 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 187 previously formed to resume dominancy thus causing reversal of the beat. LITERATURE CITED 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.