The Entry of Foreign Compounds into the Thoracic Duct Lymph of the Rat

1. Several series of structurally related radioactively labelled compounds were administered intraduodenally to rats with cannulated thoracic ducts and the radioactivity appearing in 24-hour thoracic duct lymph measured and identified.2. Radioactivity appeared in lymph following treatment with simple aromatic compounds, a series of short- and long-chain aliphatic compounds, steroids, a group of drugs, and DDT. In most cases this radioactivity was only a small percentage of the total amount absorbed from the intestinal tract. It is suggested that this appearance of radioactivity in the lymph is due to the distribution of the compounds in the total body water, of which lymph is a part.3. For compounds which enter lymph more readily (cholesterol, octadecanoic acid, octadecanol and p, p'-DDT), lipid solubility appears to be an important factor, and metabolic alterations affecting lipid solubility can affect the distribution of these compounds within the lipid and aqueous fractions of lymph. The lymphatic absorption of p, p'-DDT is dependent upon the concomitant absorption of lipids from the intestinal tract, and most of the DDT absorbed into lymph is carried in the lipid core of the chyiomicrons.