Hugh E. Vroman

Effect of allatectomy on lipid biosynthesis and turnover in the female American cockroach, Periplaneta americana (L.)

Abstract The control of the corpora allata over lipid biosynthesis and turnover was studied in the American cockroach, Periplaneta americana (L.), by using 1- 14 C-acetate as a precursor. The labelled acetate was injected into allatectomized and control roaches and the time-curve of the appearance of label in lipid fractions was determined. It was found that the greatest effect was in the triglyceride fraction, which was more than twice as much per roach in the operated insects, whereas no obvious effect was noted on the hydrocarbon fraction. Allatectomy noticeably slowed the turnover of both triglyceride and phospholipids.

The absence of cholesterol biosynthesis in a primitive insect—the firebrat, thermobia domestica (packard)

Abstract It has been postulated that certain of the more primitive insects may be capable of residual cholesterogenesis in contrast to the higher forms in which this capacity was lost through evolution. The recent report of high incorporation of dietary 1−14C acetate into cholesterol by a silverfish merited examination in another primitive insect. Hence, several groups of firebrats, Thermobia domestica (Packard) were either fed on a diet containing 1−14C acetate or injected with an aqueous solution of the labeled compound. Radioanalysis of the total lipids indicated efficient incorporation of the 1−14C acetate for lipid synthesis by both routes of administration. Gas-liquid chromatographic analysis of the nonsaponifiable lipids revealed cholesterol to be the major sterol present. After the addition of purified carrier cholesterol, the sterols were isolated from the nonsaponifiable lipids by chroma-tography on alumina and digitonin precipitation. When the sterols from all the experiments were combined and purified through the dibromide, the cholesterol had a specific activity of 3.5 cpm/mg, yielding a total incorporation of about 39 cpm. This radioactivity represents about 0.001% of that incorporated into the total lipids. It is concluded that, because of the very low levels of radioactivity remaining in the cholesterol and the inability to obtain a constant specific activity throughout the purification process, there was no significant incorporation of 1−14C acetate into cholesterol by the firebrat.

The conversion of cholestanone to cholestanol by the housefly, Musca domestica L.

Abstract Larvae of the housefly, Musca domestica L., reared aseptically on a semi-defined diet failed to develop when either cholestenone, cholestanone, or cholestanol was used as the sole source of dietary steroid. However, when these three steroids were tested for ‘sparing’ activity (in combination with a subminimal quantity of cholesterol) cholestanone and cholestanol were 66 and 79 per cent, respectively, as effective as an optimum concentration of cholesterol. Under the same conditions cholestenone showed only low biological activity (11 per cent). Biochemical studies with 4-14C-cholestanone indicate that the utilization of this steroid in the housefly larvae proceeds through its partial conversion to cholestanol. The identity of cholestanol as a metabolite of cholestanone was established by radiotracer techniques, gas-liquid chromatographic analysis, and by isolation of crystalline cholestanol from housefly pupae reared aseptically on a semi-defined diet containing cholestanone plus a subminimal amount of cholesterol. Using reverse isotope dilution techniques, no significant conversion of 14C-cholestanone to cholesterol was detected. In studies with adult insects, both males and females converted injected 14C-cholestanone to cholestanol.