THE PITUITABY BODY 



of this lobe is production of an autocoid. The extracts have more or Leas an 

 epinephrine-like action. Such extracts, rendered proteii teril- 



i/«.,|, are obtainable on the markel under the various names of pituitrin, 

 hypophysin, etc. From them a crystallizable material has been obtained, 

 I. ut this is probably a mixture of various Bubstances. In disci] the 



functions of these various extracts, it must be remembered that the inter- 

 mediary part (pars intermedia) is included with the posterior lobe in 

 their preparation. 



Although the effed of pituitary extracl on plain musch fiber and on 

 glandular tissue) appears, on first sight, to be very like that produc 

 by epinephrine, it lias been found on closer examination thai the two 

 substances really act in different ways. The rise in blood pressure p 

 duced by pituitary autacoid is likely to be more prolonged than thai 

 produced by epinephrine. It stimulates increased cardiac activity, but 

 after the vagi have been cut or sufficient atropine administered to para- 

 lyze tlirin, the pituitary autacoid continues to stimulate th< gth of 

 the heartbeat without producing the acceleration noted with epinephrine. 

 Whereas epinephrine has little or no action on the coronary - or 

 on those of the lungs, pituitary autacoid usually produces constriction 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 

 \ealed by repeating the injection after the effect of a previous one has 

 completely passed oft". With epinephrine the original effect is rep 



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

 tion is very often the reverse of that of the first: that is to say, the bl 

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



marked. Whether this effed of the Second dose is caused by the action 



of an autacoid having a chalonic rather than a hormonic influe 



whether it is due t<> a reversed effect ^\' the same hormone, it is impos- 

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

 evanescent than the liorinoiiic, and it is not cause,] by cholin. as som< 



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

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

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

 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 mus 

 whereas pituitrin nets directly mi th< involuntary muscle fibers I 



Other types of involuntary liber are also acted on by pituitrin. The 

 uterine contractions for example are stimulated Fig I 



