EXTRACTS OF THE PARS NEURALIS 



oles takes place as shown most simply by a rise in the blood 

 pressure. The degree and the duration of the contraction 

 depend to a considerable extent on the dose administered. 

 Moreover, the vascular spasm produced may affect the coro- 

 nary vessels, especially the left coronary artery,^ so that 

 tachycardia, disturbances of conduction, and cardiac dilata- 

 tion appear. As a result, the blood pressure may fall initially 

 but rises later as the coronary circulation is adequately re- 

 established and an increased or normal volume of blood is 

 pumped against the increased peripheral resistance. This 

 effect on the heart may or may not be observed, if small 

 doses of vasopressor principle are used. If posterior-lobe ex- 

 tract is injected, it may be absent or less evident, perhaps 

 because the oxytocic principle antagonizes the action of 

 vasopressor principle on the coronary arteries. 



According to Watrin and Frangois (1937), repeated sub- 

 cutaneous injections of posterior-lobe extract may be followed 

 by cardiac hypertrophy in the guinea pig. The doses used 

 (4-10 units on alternate days for 49-90 days) were large 

 enough to cause convulsions occasionally. The maximum 

 change observed was represented by a cardiac weight of 2.75 

 gm. (The weight of the heart of control animals was about 

 1.6 gm.) Enlargement of the heart was found to be due 

 to hypertrophy, not hyperplasia, of the muscle fibers. The 

 toxicity of vasopressor principle is known to be increased 

 after the administration of thyroid extract, chiefly because 

 of a change in cardiac response. Gruber, Moon, and Sufrin 

 (1935) reinvestigated this problem by studying the electro- 

 cardiographic abnormalities in non-anesthetized rabbits. The 

 histology of the hearts was also described. 



Byrom (1937) injected enormous doses of vasopressor 

 principle (5-40 units once or twice daily for 2 days or longer) 

 subcutaneously into rats. Apparently marked arterial spasm 

 locally gave rise to such pathological changes as infarction 

 and necrosis in the kidneys, liver, etc. Like other authors, 



^ See the recent articles by Frommel and Zimmet (1937). 



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