Metabolism of ecdysone and 20-hydroxyecdysone in the camel tick, Hyalomma dromedarii (Acari: Ixodidae).

Abstract

Camel ticks, Hyalomma dromedarii , utilized inoculated 14C cholesterol to synthesize apolar ecdysteroids, unknown polar ecdysteroids, and fractions coeluting with ecdysone and 20-hydroxyecdysone (20-OH ecdysone). Following inoculation into feeding virgin females, most 3H ecdysone was metabolized to nonimmunoreactive apolar compounds; lesser amounts were metabolized to 20-OH ecdysone, 20,26-dihydroxyecdysone, and possibly other unidentified ecdysteroids. Identification of these compounds was supported by coelution with authentic reference standards, coelution of radioactivity, radioimmunoassay, nuclear magnetic resonance, and infrared spectrometry of the purified fractions. Assay of the apolar ecdysteroids in extracts from ticks inoculated with 14C acetate demonstrated conjugation with carbon-containing compounds. Hydrolysis of the highly apolar ecdysteroids released 20-OH ecdysone, ecdysone, and 20,26-dihydroxyecdysone. Methylation of the hydrolysis products revealed long-chain fatty acids, especially palmitic, stearic, oleic, and linoleic acids, all confirmed by gas chromatography/mass spectrometry. The possible sites of metabolism of ecdysteroids in these ticks was investigated. Most of the ecdysteroid metabolites produced were found in the midgut (60.4%) and in the combined epidermis and fat-body tissues (31.1%). Small amounts of ecdysteroids were found in the previtellogenic ovaries of these virgin female ticks (1.5%). Ecdysone and 20-OH ecdysone were found in the hemolymph, but no apolar ecdysteroids were found in the circulatory fluids.