LEVELS OF RADIOACTIVITY IN TISSUES AND IN EXPIRED CARBON DIOXIDE AFTER ADMINISTRATION OF 1-C14-LABELLED PALMITIC ACID, 2-C14-LABELLED ERUCIC ACID, OR 2-C14-LABELLED NERVONIC ACID TO RATS

Palmitic acid -1-C14, erucic acid -2-C14, and nervonic acid -2-C14were administered to young adult rats by mouth, and levels of radioactivity in various body tissues and in respiratory CO2were determined. After [Formula: see text] hours about 20% of the label from palmitic acid and erucic acid and 30% from nervonic acid was still in the intestinal tract but after 24 hours less than 5% remained. At [Formula: see text] or 24 hours, tissue lipids of rats given palmitic acid generally contained a higher percentage of radioactivity administered than lipids from corresponding tissues of rats given erucic acid or nervonic acid. Very little radioactivity was found in brain lipids of either adult or 12-day-old rats given the labelled acids. The fatty acids were also given to adult rats by tail-vein injection and highest activities were again observed in tissue lipids of rats given palmitic acid.When given by mouth, palmitic acid contributed more radioactivity to respiratory CO2during the first 6 hours than erucic acid or nervonic acid, and peak activities did not occur until 2 to 3 hours after administration. When given by tail vein, erucic acid and nervonic acid contributed more activity to respiratory CO2than palmitic acid. Highest activities were observed during the first hour but the peak was reached somewhat later in rats given erucic acid or nervonic acid.