title: Impact on Salivary Gland Degeneration by Putative Ecdysteroid Antagonists and Agonists in the Ixodid Tick Amblyomma hebraeum
abstract: Ecdysteroids cause salivary gland degeneration in female ixodid ticks. We tested the effects of the following compounds on salivary gland degeneration in the ixodid tick Amblyomma hebraeum Koch: HHCS (22S,23S-homocastasterone), SSBR (22S,23S-homobrassinolide), STGM (2alpha,3alpha(OH)2-Delta22-stigmasten-6-one), RH 5849, and RH 5992. The first three are brassinosteroids (putative ecdysone antagonists) and the last two are nonsteroidal mimics of ecdysone in a variety of insects. In vitro, HHCS (up to 4 &mu;g/ml, 8.4 &mu;M) did not attenuate degeneration caused by 20-hydroxyecdysone; on the contrary, it enhanced the degree of salivary gland degeneration. SSBR (up to 4.5 &mu;g/ml, 9 &mu;M) likewise did not reduce 20-hydroxyecdysone mediated degeneration. RH 5849 up to 15 &mu;g/ml (51 &mu;M) and RH 5992 up to 10 &mu;g/ml (28 &mu;M) had no ecdysone-mimicking effect. In vivo, both RH compounds had an ecdysone-mimicking effect. RH 5849 (but not RH 5992) at 10 &mu;g/tick increased ovary wet weight slightly. None of the brassinosteroids displaced a significant amount of [3H]ponasterone A (PoA) from the ecdysone receptor at 6 &mu;g/ml (12-14 &mu;M) or below. RH 5849 (14 &mu;g/ml, 47 &mu;M) displaced 8% of (PoA) binding; at 68 &mu;g/ml (230 &mu;M) displacement was 30%. For RH 5992 inhibition of PoA binding was 16, 33, and 43% at 4.5, 16, and 79 &mu;g/ml (13, 45, and 79 &mu;M), respectively. Overall, the brassinosteroids and the RH compounds do not act on the tick salivary gland ecdysteroid system in a way similar to the way they act on some insect systems.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada
authors.initials: GJR
authors.lastname: Charrois
authors.initials: H
authors.lastname: Mao
authors.initials: WR
authors.lastname: Kaufman