Amitraz and its metabolite differentially activate α- and β-adrenergic-like octopamine receptors

Amitraz is a formamidine acaricide and insecticide used to control ticks, mites and fleas. N² -(2,4-Dimethylphenyl)-N¹ -methyformamidine (DPMF), a metabolite of amitraz, is thought to be an active agent that exerts acaricidal and insecticidal effects by acting as an agonist on octopamine receptors. The emergence of cattle ticks resistant to amitraz is a serious problem that requires urgent attention. The objective of this research was to determine which type of octopamine receptor is the primary target of amitraz and thereby understand the molecular mechanisms of action and resistance to amitraz.

Amitraz and DPMF potently activated Bombyx mori α- and β-adrenergic-like octopamine receptors (α- and β-AL OARs) that were stably expressed in HEK-293 cells. Notably, DPMF elevated intracellular cAMP levels, with an EC₅₀ of 79.6 pm in β-AL OARs, the transcripts of which were prevalently and widely localised in B. mori body parts. Furthermore, DPMF elevated the intracellular Ca²⁺ levels, with an EC₅₀ of 1.17 nm in α-AL OARs.

Although both amitraz and DPMF acted as OAR agonists, the metabolite DPMF was more potent than amitraz and differentially activated α- and β-AL OARs. The present findings provide a basis for studies to examine the mechanism of amitraz resistance and to develop novel acaricides and insecticides. © 2016 Society of Chemical Industry.