Dietary cholesterol utilization by the housefly,Musca domestica

The amount of cholesterol and the distribution of its metabolites were studied in various larval tissues of the housefly (Musca domestica), reared on a high cholesterol diet containing the radioactive cholesterol. The sterol content was also examined in adults derived from larvae reared on increasing dietary cholesterol concentration in separate batches. The results suggest that when the dietary sterol concentration was raised from 0.002 to 0.02% wet weight (an optimal concentration required for a maximal growth and development of insect), the sterol content of six-day old larvae was increased approx. 4-fold. However, a further 10-fold increase of dietary cholesterol (to 0.22% of wet weight) was associated with only a 1.5-fold increase in larval sterol content, and no increase in the sterol content of adult insects derived from such larvae was observed. This increase of sterol content of whole larvae was found to be confined to the larval cuticle and composite gut fractions and may be attributed to unabsorbed cholesterol in the gut, and to a solubilizing effect of the cuticle. These findings suggest that when the cholesterol requirement for the maximal growth of the insect has been reached, larvae are able to regulate the intake of ingested cholesterol, and no more is taken up through the gut even when a high gut concentration of cholesterol is present.The adults contained a higher percentage of esterified sterols than the larvae, approx. 25% of the sterol in females and 14% of sterol in males were esterified.