PHYSIOLOGIC IMPORTANCE OF LYMPH 



1045 



These calculations showed that protein left the circu- 

 lation at the rate of 77, 142, and 11 mg per hour in 

 the liver, intestine, and cervical tissues, respectively, 

 or a total leakage of 230 mg. In another cat, 2540 mg 

 of injected fat left the circulation within 2 hours 

 during which time the leakage of protein was 448 mg. 

 It is obvious that fat in chylomicron form can dis- 

 appear from the blood stream much faster than pro- 

 tein. The chylomicron fraction of lymph appears to 

 carry neutral fat (233). 



Reinhardt el al. (182) injected biosynthesized 

 P 32 -Iabeled phospholipid into a peripheral vein of 

 rats with thoracic duct fistula and reported that 9 to 

 20 per cent of the injected phospholipid could be 

 recovered in the thoracic duct lymph in the succeed- 

 ing 3 to 6 hours. McCandless & Zilversmit (131) 

 obtained labeled lymph by feeding dogs with re- 

 labeled triolein. The labeled lymph was administered 

 to recipient dogs, and the rate of disappearance of 

 the lymph lipids from plasma was followed. Lymph 

 t 131 triglycerides were found to disappear from the 

 circulation rapidlv, with an initial half-time of several 

 minutes. Disappearance of I 131 phospholipids was 

 slower as determined in the same animals, 10 to 40 

 per cent of the injected dose remaining in the blood 

 1 to 2 hours after injection. These results were similar 

 to those previously obtained by the same authors 

 using artificially prepared fat emulsions (130). 



The presence or absence of bile appears to influence 

 the pattern of absorption and lymph transport of 

 dietary soaps and triglycerides in the dog. Rampone 

 & Sigurdson (179) recently reported that the ab- 

 sorption of triolein and sodium oleate was signifi- 

 cantly diminished in the absence of bile. In the normal 

 dog, 90 per cent of fed triolein and 94 per cent of 

 fed sodium oleate were recovered from the thoracic 

 duct as lymph lipid. In dogs with bile fistula only 8 

 per cent of fed triolein was recovered in lymph com- 

 pared to 40 per cent of sodium oleate. 



The route of absorption of steroids from the gas- 

 trointestinal tract seems to be determined largely by 

 the chemical nature of the compounds. Methyl 

 testosterone, 1 7a-methylestradiol and cortisone-4-C 14 

 acetate are absorbed in the rat by way of the portal 

 circulation (23, 24, 102). Studies in human subjects 

 have shown that testosterone, cortisone, and cortisone 

 acetate are also absorbed in this manner and are 

 virtually absent from lymph (97). In contrast, ab- 

 sorption of cholesterol into lymph of the rat (17, 41) 

 and dog (152) accounts for essentially all the sterol 

 that enters these species from the diet. This is also 

 true for man (98). Data from the different species 



studied is consistent in showing that much of the 

 cholesterol is esterified by the intestinal mucosa (25, 

 41, 98, 213). A number of factors appear to influence 

 the lipid composition of lymph during cholesterol 

 absorption (212). In rats given intragastrically 

 emulsions containing cholesterol, oleic acid, and 

 sodium taurocholate, addition of albumin resulted 

 in a rapid increase in total lymph lipid which was 

 much more marked than in those animals not re- 

 ceiving albumin. The amount of lymph cholesterol, 

 however, was less for a 24-hour period. The presence 

 of taurocholate and oleic acid in administered emul- 

 sions resulted in elevation of ester cholesterol, indi- 

 cating increased absorption of endogenous cholesterol 

 (211). Addition of cholesterol to the emulsions also 

 resulted in further significant increase in the ester 

 cholesterol fraction in thoracic duct lymph. In 

 further studies (207), it was shown that small doses 

 of fed cholesterol-4-C 14 lead to labeling of cholesterol 

 fractions of mucosa and lymph without an increase 

 in the level or turnover in lymph. Feeding tracer 

 dose with oleic acid and sodium tauracholate in- 

 creases the turnover rate of the pool which leads to an 

 increased amount of labeled and unlabeled cholesterol 

 in lymph. In fasting rats, the major fatty acids in 

 lymph are palmitic, linoleic, and oleic acids with 

 polyunsaturated fatty acids comprising 36 per cent 

 of the total cholesterol fatty acids (206). After feeding 

 oleic acid only 42.3 per cent of the total was present 

 as oleic acid. The total cholesterol fatty acid composi- 

 tion of lymph is evidently determined not only bv 

 dietary fatty acid, but by the composition of the fatty 

 acid pool in the mucosa from which fatty acids are 

 drawn for esterification of cholesterol, a suggestion 

 which had been made earlier bv previous workers 



(30). 



Bloom el al. (22) fed unanesthetized rats C 14 - 

 labeled stearic and myristic acids and found that 

 nearly all the absorbed C 14 was recovered in intestinal 

 lymph. This finding, taken in conjunction with earlier 

 work with labeled palmitic and pentadecanoic acids, 

 showed that lymph is the major if not the exclusive 

 agent for the transport of absorbed long-chain fatty 

 acids. On the other hand, when similar experiments 

 were carried out with labeled lauric acid and decanoic 

 acid, recoveries of the absorbed C 14 amounted to 15 

 to 55 and 5 to 19 per cent, respectively. Since it was 

 shown that the findings were not the result of bacterial 

 action, it would appear that the major portion of a 

 short-chain fatty acid is transported via the blood 

 stream from its site of absorption. Blomstrand et al. 

 (21) have extended this type of study to man. They 



