Studies with Radioactive Iodized Fat. I. Preparation of Radioactive Fat with Observations on the Absorption of Fat following Subcutaneous and Intraperitoneal Injection in Dogs.

The intravenous administration of emulsified fat in concentrations suitable for nutritional purposes is not applicable for clinical use because an emulsion stabilizer free of undesirable effects has not yet been developed. Pending the availability of a satisfactory stabilizer, the possibility of parenteral administration of fat by other routes deserves further exploration. Data reported on the absorption and distribution of fat given subcutaneously, intramuscularly and intraperitoneally to animals (1-6) are equivocal or conflicting largely because of the inadequacy of the quantitative analytical methods used. Fat labelled with a radioactive element can be traced and measured with considerable accuracy. While fat labelled with radioactive carbon (C14) (7) or deuterium (8) is ideal, the measurement in tissue is more difficult than that of fat labelled with radioactive iodine. Although iodized fat is unnatural, its digestion, absorption and metabolic fate after oral and parenteral administration is said to simulate closely that of natural fat (9-15). Since iodine is liberated relatively slowly from iodized fat (16), it should, if radioactive, be useful to follow the absorption and immediate distribution of fat, once it enters the circulation. Accordingly, an emulsion of fat labelled with radioactive iodine was prepared with Demal 14 2 in order to determine with reasonable accuracy, (1) the absorption and distribution of fat introduced subcutaneously or intraperitoneally, and (2) the distribution of radioactive fat emulsions introduced intravenously. This communication presents a method for the preparation of radioactive fat, to-