FUNCTIONAL CHANGES IN STRICTURE 83 



that of proteolytic enzyme? 2) Is the discharge of the /ymogen granules aUercd accord- 

 ing to the nature of the meal given after starvation, that is, by liigh protein, fat or 

 carbohydrate? 



Dr. Pai.adk: /) No, but evidence answering in part your question has liecn obtained 

 by Hokin (13) and by Laird and Iiarlon (i^). According to their Inulings, amylase and 

 lipase are present in the zymogen granules although in smaller relative amounts than 

 the proteolytic zymogens. 2) As far as I know, the influence of the nature of the meal 

 upon the zymogen discharge has not been studied by electron microscopy. Earlier work, 

 carried out with the light microscope, has established that there is extensive discharge 

 of zymogen granules when peptones, soaps or carbohydrates are introduced in the duo- 

 denum but not when acid is instilled therein (i). 



Dr. Swift: How do you postulate the mechanism of zymogen material ejection? Is 

 this a mechanical event similar to muscular contraction? If fluids are brought back in to 

 replace zymogen material how are they sucked in? 



Dr. Palade: At present there is no evidence of contractile structures in the apical 

 region of the acinar cell. It is, however, reasonable to assume that the cell membrane 

 itself (and the membrane limiting the zymogen granules) may be contractile and may 

 thereby help in the ejection of the zymogen. The mechanism by which vesicles move 

 from the centrosphere region to the cell surface and back is entirely unknown. The 

 fusion of the membrane of the zymogen granules with the cell membrane and the 

 subsequent discharge of their content seem to be, however, under chemical control: 

 zymogen discharge is greatly accelerated by acetylcholine and carbamylcholine (i, 34). 



