THE PITUITARY BODY 811 



lyze them, the pituitary autacoid continues to stimulate the strength of 

 the heartbeat without producing the acceleration noted with epinephrine. 

 Whereas epinephrine has little or no action on the coronary vessels (page 

 268) or on those of the lungs, pituitary autacoid usually produces constric- 

 tion of both types of vessel ; and on the renal arteries the actions of the two 

 autacoids are entirely different, for epinephrine has a marked constric- 

 ing effect, while the pituitary autacoid produces dilatation. 



Another striking difference in the extracts from the two glands is re- 

 vealed by repeating the injection after the effect of a previous one has 

 completely passed off. With epinephrine the original effect is repro- 

 duced; with pituitrin, on the other hand, the effect of the second injec- 

 tion is very often the reverse of that of the first; that is to say, the blood 

 pressure, instead of rising, may fall, or the rise be very much less 

 marked. Whether this effect of the second dose is caused by the action 

 of an autacoid having a chalonic rather than a hormonic influence, or 

 whether it is due to a reversed effect of the same hormone, it is impos- 

 sible at present to say. The chalonic effect in any case is much more 

 evanescent than the hormonic, and it is not caused by cholin, as some 

 have suggested. The effect of epinephrine, it will be remembered, is 

 abolished by ergotoxin and apocodeine. These drugs, on the other hand, 

 have no influence on the action of pituitrin. The difference in action 

 between the two autacoids is usually explained by assuming that the 

 epinephrine acts on the receptor substance associated in some way with 

 terminations of the sympathetic nerve fibers in involuntary muscle, 

 whereas pituitrin acts directly on the involuntary muscle fibers themselves. 

 Other types of involuntary fiber are also acted upon by pituitrin. The 

 uterine contractions, for example, are stimulated (Fig. 199), this effect 

 being unconditioned by the state of the uterus. 



A similar effect is produced upon the musculature of the intestine 

 and bladder (in contrast to the inhibitory effect of epinephrine) and 

 upon the muscle of the ureter. Pupillary dilatation of the excised frog's 

 eye, but not of the mammal's, is produced by pituitrin. The effect of this 

 substance upon the bronchioles is shown in Fig. 200. 



The glands upon which pituitrin has the most pronounced action are the 

 mammary glands and the kidneys. It has no influence upon the salivary 

 secretion. The effect on the kidney is evidenced by the remarkable increase 

 in the urinary flow following injection of the pituitrin. This diuresis might 

 of course be due merely to the vasodilatation that we have seen such extracts 

 produce a vasodilatation which is all the more marked because the vessels 

 elsewhere in the body undergo constriction. But pituitrin continues to cause 

 increased urinary outflow in the absence of any demonstrable vascular 

 change; it also acts after the administration of atropine, so that it is con- 

 sidered by some observers to act on the excretory epithelium of the convo- 



