PHYSIOLOGIC IMPORTANCE OF LYMPH 



I°49 



only an insignificant amount appearing in thoracic 

 duct lymph. Similar conclusions were reached by 

 Reizenstein et al. (183). Koler & Mann (115) found 

 that the iron content of intestinal lymph of cats 

 maintained on a normal diet was relatively constant 

 over periods as long as 7 days. At lymph outputs of 

 1 ml per hour, there was an hourly output of 0.5 ^ig 

 of iron. Peterson & Mann (174), using radioiron, 

 found that only an insignificant portion of an orally 

 administered amount of radioiron appeared in the 

 lymph of rats with total intestinal-lymph fistulas — 

 less than o. 1 per cent of the total amount of radioiron 

 administered and only 2.0 to 5.0 per cent of the total 

 amount of iron absorbed from the gastrointestinal 

 tract after 8 hours. Everett et al. (69) confirmed 

 these results in the rat. The absorption of subcutane- 

 ous FeCl 3 occurred primarily via the blood vessels, 

 but subcutaneous plasma-bound iron passed almost 

 exclusively into the lymphatics. Intravenously ad- 

 ministered iron appeared rapidly in the lymph. 

 These observations and those of previous workers are 

 unquestionably related to the fact that iron is nor- 

 mally bound to protein in plasma. Since proteins 

 leak slowly from blood capillaries, we would expect 

 to find small quantities of iron-protein compounds 

 in lvmph from all areas. Since the capillaries of the 

 intestine are more permeable to protein than those 

 of other areas, and since protein leakage is greatest 

 in the liver, larger amounts would be present in 

 intestinal, hepatic, and thoracic duct lymph. It is 

 also of interest that Everett and co-workers found no 

 evidence that leukocytes played more than a negligible 

 role in iron absorption regardless of the method of 

 iron administration. 



Miscellaneous 



Scattered reports deal with a variety of substances 

 transported in lymph. Thus Salter (193) reported 

 that the protein-bound iodine per gram of protein in 

 cervical lymph was concentrated relative to the 

 homologous serum value. Klitgaard et al. (113, 114) 

 found that about 3 per cent of a subcutaneously 

 administered dose of thyroxin-C 14 appeared in 

 thoracic-duct lymph in rats during an 8-hour experi- 

 mental period. The level of radioactivity in lymph 

 was lower than in plasma on a volume basis but 

 significantly higher when calculated on the basis of 

 protein content. Chromatographic analysis of lymph 

 samples showed the radioactivity present to be from 

 unaltered thyroxin. It would be interesting to know 



the extent to which other protein-bound hormones are 

 transported in lymph. We can assume that small 

 quantities escape from the capillaries as do other 

 macromolecules and are returned via the lymphatic 

 system. 



Dietrich & Siegel (53) recently reported an in- 

 teresting study designed to determine whether 

 nucleotides or nucleotide precursors synthesized in 

 an organ or tissue, e.g. liver, were available to nourish 

 other tissues and organs. The stimulus for their 

 studies arose from observations that certain cell 

 types cannot utilize free bases and must secure the 

 nucleoside containing the base from an external 

 source, apparently other cell types. They argued that 

 if bases and other nucleotide precursors are secreted 

 by a distant organ or cell type, these compounds 

 may be present in both the blood and lymph which 

 bathes the cell or organ. Blood, however, contains 

 such a mass of living cells that it is difficult to deter- 

 mine whether intermediates found in the plasma 

 are derived from the cells within the blood or from 

 other somatic cells nourished by and yielding their 

 products to the blood. Since the cell population in 

 lymph is insignificant when compared with that of 

 blood, it might be assumed that metabolites found 

 in the lymph would reflect more closely the metabo- 

 lism of the tissue through which it has passed than 

 that of the lymphocytes. Working on rats anesthetized 

 with Nembutal, they injected glycine-2-C 14 and nico- 

 tinamide-7-C 14 and found adenine, guanine, cytosine, 

 uracil, and uric acid in measurable amounts in 

 thoracic duct lymph. Xo detectable quantities of 

 nucleosides were observed. The quantity of acid- 

 soluble nucleotides found was equivalent to that 

 which would be expected from the lymphocytes 

 present in the lymph samples analyzed. Lymph 

 collected for a 45-hour period following the injection 

 of carbon-labeled glycine contained no significant 

 amount of labeled purine derivatives. At the end of 

 this period, however, liver tissue still contained 

 appreciable quantities of labeled acid-soluble nu- 

 cleotides. Lymph collected for a similar period of 

 time after the injection of carbon-labeled nicotinamide 

 contained very small amounts of radioactivity. While 

 the results raised many unexplainable questions and 

 suggested the need of further work, they did confirm 

 previous investigations of plasma in indicating that 

 if these compounds are essential for the proper nutri- 

 tion of certain cell types, these purine derivatives are 

 not transported from sites of synthesis, such as the 

 liver, via the lymphatic ducts. 



