The Action of Extracts of the Posterior Lobe of the Pituitary Body on the Pulmonary Circulation

Abstract

1. The effect on the circulation of the substance separable by alcohol from the posterior lobe of the bovine pituitary, and the effect of the residue after such separation, has been examined in many experiments on the cat, dog, and rabbit, and in one experiment on the monkey. 2. The alcohol‐extract, when dried and dissolved in water, reproduces in all respects the action of histamine. 3. The residue after extraction with alcohol, when dried and dissolved in water, differs somewhat in its action in the species examined. 4. In the cat, extracts of histamine‐free residue always cause a rise of aortic pressure, and generally a slight fall of pulmonary pressure as well. Occasionally there is no effect produced on the pulmonary pressure; and in one experiment on a decerebrated cat the fall was replaced by a rise, relatively as great as that produced in the aortic pressure. In all animals the rise in aortic pressure is often interrupted by a “dip” somewhat like that caused by stimulation of the splanchnic. This "dip" we have found to be abolished in the cat after tying off the suprarenal capsules; a dose of pressor substance then causes an uninterrupted and prolonged rise in both pulmonary and aortic pressures. We have, however, performed an insufficient number of experiments to prove conclusively that the “dip” is due to the secretion of adrenaline. 5. In the dog and rabbit the histamine‐free substance always produces a distinct fall in pulmonary pressure, often very well marked. In these animals the aortic pressure first rises rapidly and then falls even below the original pressure. The fall in question is not to be confused with the above‐mentioned “dip” in the curve of rising aortic pressure, which may or may not occur as well. After the fall the aortic pressure rises steadily and progressively, and may attain a great height, the pulmonary remaining low. In some cases this progressive rise is replaced by a series of slow and large fluctuations in pressure, somewhat like those which have been described in perfused surviving vessels. 6. Some of these differences are explained when the effects produced on the heart are observed and recorded. In the cat, the effect on the heart is generally slight and may be absent; in the dog and rabbit the heart is slowed and markedly weakened, and although the slowing may be abolished by atropine the weakening is not thereby abolished, or at least far less readily. 7. It is well known that the effect of a first adequate dose of histamine‐free substance in producing contraction of the blood‐vessels is not repeated as the result of subsequent doses given within a certain time after the first dose (tachyphylaxis). This, we find, is also true for the effects on the heart. In other words, the result of a first sufficient dose of this substance, both upon the blood‐vessels and heart, is to establish immunity to the effect of subsequent doses, an immunity which requires a considerable time to pass off. 8. In the single experiment which we were able to make upon a monkey (the animal had alre...