Biosynthesis and distribution of ecdysone and 20‐OH‐ecdysone in Aedes aegypti

Abstract

AbstractThe distribution and biosynthesis of ecdysone and 20‐hydroxyecdysone (20‐OH‐ecdysone) was followed in sugar‐ and blood‐fed female Aedes aegypti. In both sugar‐ and early blood‐fed animals most of the ecdysteroid determined by radioimmunoassay was found outside the ovary. Twenty‐four to 40 h after blood feeding, however, ecdysteroid was distributed between ovary and carcass in the ratio of 1:1.5. Ecdysteroid titer reached a plateau between 18 to 40 h after the blood meal and decreased thereafter. Analysis of the ecdysteroid titer using thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) revealed that both 20‐OH‐ecdysone and ecdysone were synthesized after the blood meal. The ratio of 20‐OH‐ecdysone to ecdysone remained essentially constant and fluctuated in parallel throughout egg development. Chromatography of the early ecdysteroid peak (8 h after feeding) using TLC and HPLC indicated that although it cross‐reacted with ecdysteroid antibodies, it did not have the same elution times as ecdysone and 20‐OH‐ecdysone and is, therefore, probably a precursor of these ecdysteroids. Injections of egg development neurosecretory hormone (EDNH) preparation purified to near homogeneity, into ligated abdomens, induced ecdysteroid synthesis only if the abdomens were first treated with methoprene (12.5 pg). Methoprene at this concentration did not stimulate ecdysteroid synthesis in these abdomens. When blood‐fed females were treated with [4‐14C] cholesterol and analyzed using TLC and HPLC procedures, both [14C]labeled ecdysone and [14C]labeled 20‐OH‐ecdysone were synthesized in the ratio of 1:1.5. This report is the first to show that both ecdysone and 20‐OH‐ecdysone are synthesized in vivo in female A. aegypti.