THE PITUITARY BODY 767 



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

 epinephrine-like action. Such extracts, rendered protein-free and steril- 

 ized, are obtainable on the market under the various names of pituitrin, 

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

 but this is probably a mixture of various substances. In discussing 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 effect of pituitary extract on plain muscle fiber (aiid on 

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

 by epinephrine, it has been ifound on closer examination that the two 

 substances really act in different ways. The rise in blood pressure pro- 

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

 produced by epinephrine. It stimulates increased cardiac activity, but 

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

 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 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 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 on by pituitrin. The 

 uterine contractions for example are stimulated (Fig. 197) ; so are those of 



