The Utilization and Metabolism of 4-C14-Cholesterol by the Adult House Fly

The metabolism and excretion of ingested 4-C14-cholesterol was studied in the house fly (Musca domestica L.). Only low levels of excretion (2.0%-2.5%) were found 3 days after treatment, and about 10% of this behaved as acidic material. When female flies were treated and the eggs collected, 78% of the radioactivity was recovered 3 weeks after treatment. The high recoverv and low excretion rate indicate, a strict sterol economy in the house fly. The administered cholesterol was efficiently utilized in egg production. Some of the radioactive sterols were found to be esterified in both the egg and adult. Analysis by column chromatography and reverse isotope dilution demonstrated the presence of two major compounds—unchanged cholesterol and 7-dehydrocholesterol—and a lesser fraction consisting of unidentified polar steroids.