Source of Fat Found in the Thoracic Duct Lymph in Fasting

Abstract

Thoracic duct lymph of fasting dogs contains 0.3 to 1.3% total fatty acids. 1 Further observations showed that with the continuous collection of the lymph under anesthesia, there is usually a spontaneous decline in the lipid content, amounting to 50% or even more in 4 hours. Injection of pilocarpine or secretin is followed by an increase of the lipid content of the lymph up to or considerably above the initial level, the maximum effect appearing about 4 hours after the injection. In enterectomized animals, the initial lipid content is low and does not rise following pilocarpine; nor does pilocarpine cause a rise of lipids in the lymph of dogs with common bile duct fistula.

Method. 26 dogs were fasted 3 to 8 days. Cannulation of the thoracic duct was done under nembutal anesthesia. For the preparation of the enterectomized animals, the bowel was removed from the recto-sigmoid junction to the midportion of the duodenum, the free end of the duodenum being brought to the outside through a stab wound. The animal was allowed to recover and was fasted several days, fluid being given twice daily subcutaneously. The dose of pilocarpine was 1 mg. per kilo and that of the secretin 60 dog units total intravenously. Total fatty acids and cholesterol were determined by Bloor's oxidation method.

The finding that the thoracic duct lymph of fasting enterectomized animals is clear, and low in lipids indicates that the principal source of the milky lymph in fasting is the bowel. Furthermore, the effect of pilocarpine and secretin suggests that the lipids of the lymph come from the lumen of the bowel; in the first place when the bile is shunted to the outside, the lipid content in the lymph is low and does not rise with pilocarpine; in the second place, the delay in the appearance of the maximum lipid content after pilocarpine and secretin is consistent with the known effects of these agents on intestinal secretions.