Impact on Salivary Gland Degeneration by Putative Ecdysteroid Antagonists and Agonists in the Ixodid Tick Amblyomma hebraeum

Pesticide Biochemistry and Physiology
G J R CharroisW Kaufman

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 μg/ml, 8.4 μM) did not attenuate degeneration caused by 20-hydroxyecdysone; on the contrary, it enhanced the degree of salivary gland degeneration. SSBR (up to 4.5 μg/ml, 9 μM) likewise did not reduce 20-hydroxyecdysone mediated degeneration. RH 5849 up to 15 μg/ml (51 μM) and RH 5992 up to 10 μg/ml (28 μM) had no ecdysone-mimicking effect. In vivo, both RH compounds had an ecdysone-mimicking effect. RH 5849 (but not RH 5992) at 10 μg/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 μg/ml (12-14 μM) or below. RH 5849 (14 μg/ml, 47 μM) displaced 8% of (PoA) binding; at 68 μg/ml (23...Continue Reading

Citations

Mar 12, 2004·Annual Review of Plant Physiology and Plant Molecular Biology·Steven D. Clouse, Jenneth M. Sasse
Apr 10, 2012·Experimental Parasitology·Gislaine Cristina RomaMaria Izabel Camargo-Mathias

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