PHYSIOLOGIC IMPORTANCE OF LYMPH 



IO47 



that filter constantly across the walls of blood vessels, 

 or from local structural changes inherent in the vessel 

 wall, or the result of age or disease, that serve to 

 hamper the normal passage of these fatty substances." 



Enzymes 



Many enzymes are found in lymph in small con- 

 centrations (234). Their concentrations are usually 

 higher in intestinal and liver lymph than in cervical 

 or leg lymph, but are usually lower than in plasma 

 and run parallel with the concentration of proteins 

 (18, 28). It is probable that, in most instances, these 

 substances have leaked from the blood stream and 

 take part in the extravascular circulation via the 

 lymphatics. 



On the other hand, certain enzymes seem to be 

 transported to the blood stream from their cells of 

 origin via the lymph. Flock & Bollman (74) made 

 an interesting comparison between the activity of 

 rat intestinal lymph with respect to amylase and 

 tributyrinase. The activities of the two enzymes in 

 intestinal lymph are generally less than in plasma. 

 The 24-hour secretion of amylase in lymph is greater 

 in fed than in fasting rats, but much of the increase 

 is due to the increase in lymph volume. External 

 drainage of lymph for 2 days does not significantly 

 alter the plasma amylase level. On the other hand, 

 although the 24-hour secretion in lymph of tributy- 

 rinase is also much greater in fed than in fasting rats, 

 it appears to represent a specific effect of ingested 

 fat on the chemical composition of intestinal lymph. 

 External drainage of the lymph markedly decreases 

 the tributyrinase content of plasma. These results are 

 similar to those previously obtained by the same 

 authors with respect to alkaline phosphatase (72). 

 The increase of alkaline phosphatase of intestinal 

 lymph following the feeding of fat is abolished or 

 greatly diminished when the bile duct is ligated or 

 the bile drained away in a biliary fistula (73). The 

 presence of bile thus seems to be essential for the 

 release of alkaline phosphatase from the intestinal 

 mucosa. 



The histaminase activity of lymph has received 

 considerable attention from Carlsten and his col- 

 leagues. They were led to these studies by their failure 

 to demonstrate the presence of histamine in venous 

 blood during reactive hyperemia and muscular 

 tetanus, where histamine was alleged by some in- 

 vestigators to be liberated. They then turned to 

 lymph on the grounds that lymph is closer to the tissue 

 cells which are thought to liberate histamine, and 



therefore histamine should accumulate in greater 

 concentration in lymph than in plasma. They used 

 dogs, anesthetized with Nembutal, and collected 

 lymph from the thoracic duct (37). Lymph had no 

 histamine in detectable amounts. In contrast to 

 guinea pigs, rats, and rabbits, dogs show low plasma 

 histamine activity. The plasma histamine concentra- 

 tion could be raised to very high levels by histamine 

 infusion or by intravenous injection of histamine 

 liberators (curare and trypsin) without the appear- 

 ance of detectable amounts of histamine. Study of 

 the histaminolytic activity of the lymph showed it 

 to be more than 30 times as powerful as in plasma 

 when tested in vitro. In vivo, intralymphatically 

 administered histamine was inactivated at a very 

 high rate. This same group has also used cats and 

 have described a simple micromethod for estimation 

 of the small amounts found in lymph and plasma 

 (38, 231), and showed that the histaminolytic activity 

 of lymph is not changed by routine procedures such 

 as anesthesia, laparotomy, gentle handling of the 

 viscera, or by reactive hyperemia or pregnancy (35, 

 232). Adrenalectomy is followed by a marked increase 

 in histaminase content of thoracic duct lymph (but 

 not in plasma) which reaches a maximum within 2 

 hours and persists approximately 24 hours (36). In- 

 fusion of an adrenocortical extract will reverse this 

 increased activity (39). The histaminolytic activity 

 of cervical and leg lymph is less than that of the 

 thoracic duct and seems to originate from the kidneys 

 and gut (34). 



It has been suggested that the lymphatic transport 

 of lipase may be concerned with the changes seen 

 in disseminated pancreatic fat necrosis (171). So- 

 called pancreatic and peripancreatic fat necrosis is 

 supposedly due to the splitting of neutral fat into 

 glycerol and free fatty acid by pancreatic lipase 

 which has escaped from the injured pancreas. The 

 free fatty acids are thought to combine subsequently 

 with calcium in the tissue and tissue fluids to form 

 insoluble calcium soaps which give rise to the opaque 

 white areas seen in the fat depots of the abdominal 

 cavity and elsewhere. Perry made intraperitoneal 

 injections of a mixture of pancreatin and graphite 

 suspension in rats and at necropsy found multiple 

 areas of fat necrosis in the abdominal and thoracic 

 cavities, closely associated with graphite-delineated 

 lymph channels. The evidence of the participation 

 of the lymphatics in this disease is quite suggestive 

 and indicates the desirability of further investigation 

 of the role of lymphatics in this and other diseases. 



Reizenstein el al. (183) recentlv reported experi- 



