1. In the rabbit adrenalin injected in moderate doses into the jugular vein at first either causes a rise of pulmonary blood‐pressure, owing to its constricting effect on the pulmonary arterioles, or may show no effect upon the pulmonary system. But with the great constriction of the systemic arterioles which it produces when it reaches them, any rise in the pulmonary system is rapidly converted into a fall, gradual recovery following as the constriction of the systemic arterioles passes off. When injected into the aorta through the carotid the effects are similar, but the preliminary rise in pulmonary pressure due to the constriction of the pulmonary arterioles is absent. But sometimes the effects seen in the rabbit are similar to those ordinarily seen in the cat and dog (see below).2. Although in the cat the effects which have just been mentioned as most common in the rabbit are sometimes seen, the usual result is the production—whether the autacoid be injected into the jugular vein or into the aorta through the carotid—of a sharp, well‐marked rise in both pulmonary and aortic pressures, the rise being sometimes preceded in the case of the intravenous injection by a slower elevation of the pulmonary curve, and in the case of the arterial injection by a similar commencing rise in the aortic curve. These preliminary elevations, when seen, are no doubt due to commencing constriction of the respective arterioles; but the very marked and sharp rise which almost always occurs in both pulmonary and aortic curves, and which usually shows parallelism in both systems— not only in the main rise and fall but also. in the fluctuations which are often seen—must be of cardiac origin.With unusually small doses a fall of pressure may be obtained in both pulmonary and aortic systems.3. In the dog there occurs, as the result of the intravenous injection of a fairly large dose of adrenalin, a great rise of pressure in both systems, sometimes running almost parallel, sometimes better marked in the pulmonary than in the aortic system. Occasionally, in the dog as in the cat and rabbit, when an injection is made into a vein, the commencement of the rise is very distinctly in advance in the pulmonary, and when into an artery, the commencement of the rise is seen first in the aortic system; but in many instances the rise is simultaneous in both. We have not observed in the dog either a fall in the pulmonary pressure with the rise in the aortic—which is the common effect in the rabbit and is occasionally seen in the cat—nor the simultaneous fall in both pulmonary and aortic pressures which we have occasionally seen in the cat. But the number of experiments we have made on dogs has been much more limited in number than those on cats.4. The rise in the pulmonary system is not due to “back action” propagated from the aortic system. For there may be no rise at all in the pulmonary, with great rise in the aortic system. This is true not only for adrenalin, but also when the pressure in the aortic system is raised by mechanical compression of the aorta and in other ways.5. In rabbits the chief effects of adrenalin upon both pulmonary and aortic pressures are produced upon the blood‐vessels, but in most cats and in dogs the chief effects are produced by the action of the autacoid on the cardiac musculature. There are, however, distinct effects upon the vessels both of the pulmonary and aortic systems, but these are generally obscured by the cardiac effects, although in some individuals they become more prominent. Whether these differences in individuals have anything to do with the anæsthetic or not we are not at present in a position to determine.6. Many of our tracings afford evidence that the musculature of the two sides of the heart may be differently affected by adrenalin. It is possible that this difference of effect may be due to the action of the autacoid upon the Purkinje network of the ventricles.
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Oct 1, 1972
Thomas B Watt + 1
Open Access
