Distribution and dynamic state of sterols and steroids in the tissues of an insect, the roach Eurycotis floridana

The total concentrations of sterols in the tissues of the roach, Eurycotis floridana, reared under aseptic conditions and on semisynthetic diets, are similar to, but somewhat lower than, those of tissues of vertebrates.Total concentrations of tissue sterols are relatively independent of dietary concentration of sterols whether the diet contains 0.1% cholesterol as the sole sterol, or a ``minimal cholesterol'' mixture (0.1% cholestanol together with 0.005% cholesterol). Under the latter conditions the cholesterol is incorporated preferentially into most tissues and remains almost exclusively unesterified, while the cholesterol-sparing sterol is esterified to varying degree, depending upon the tissue.The turnover of tissue sterols has teen studied. Cholesterol of the tissues of adult insects grown on a diet containing this sterol alone may be displaced by cholestanol fed as 5% of the total diet, initially at an appreciable rate but later much less rapidly. In growing insects that have received a diet containing cholestanol together with minimal cholesterol, the unesterified cholesterol turns over slowly in all tissues and immeasurably slowly in some. The unesterified sparing sterol, on the other hand, turns over at a much greater rate. The turnover of sterols during growth is accompanied by a shift of sterols from the unesterified to the esterified pool in all tissues.The fat body of the growing insect stores sterols (apparently as their esters) that have been displaced from other tissues. The fat body of the adult does not show evidence of sterol storage.Polar derivatives of sterols are present in minor amount in all tissues of the insect, most abundantly in the mid-intestine and gastric caeca. These compounds seem likely to be C27 steroids.The results are discussed in terms of the concept that the sterols incorporated into the tissues of this insect function primarily as components of subcellular membranous structures. It seems likely that unesterified cholesterol is a tightly bound and highly specific component of such structures, while the unesterified cholesterol-sparing sterol is less firmly bound into the same structures or into others of lesser general stability.