title: Catabolism of dopamine and 5-hydroxytryptamine by monoamine oxidase in the ixodid tick, Amblyomma hebraeum.
abstract: The purpose of this study was to assess biogenic amine catabolism in Amblyomma hebraeum Koch (an African cattle tick). We assayed haemolymph and saliva for a variety of biogenic amines (usually following injection of substrate into the haemolymph) in partially fed females using HPLC coupled to electrochemical detection. Dopamine (DA) and 5-hydroxytryptamine (5-HT) were rapidly converted to dihydroxyphenylacetic acid (DOPAC) and 5-hydroxyindoleacetic acid (5-HIAA) respectively, indicating that monoamine oxidase (MAO) constitutes a major catabolic pathway for biogenic amines in this species. We could not detect N-acetylated or gamma-glutamyl conjugated metabolites of these important neurotransmitters. [In a few samples we looked for but could not detect homovanillic acid or 3-methoxytyramine (O-methylated metabolites of DOPAC and DA respectively).] Deprenyl was about 44-72 times more potent an inhibitor of MAO than clorgyline when either DA or 5-HT was offered as substrate, suggesting that this MAO is of the MAOB type. Conversion of DA to DOPAC was also detected in several tissues incubated with DA in vitro; in descending order of MAO activity (pmol mg-1 h-1 at about 18 degrees C) tissues tested were: skeletal muscle (approximately 100), Malpighian tubule (approximately 50), ovary (approximately 45), salivary gland (approximately 30), midgut (approximately 20), and haemolymph (approximately 4-5). This study suggests that ticks differ considerably from insects in utilizing MAO as an important metabolic pathway for biogenic amines.
authors.affiliation: Department of Biological Sciences, University of Alberta, Edmonton, Canada.
authors.forename: R
authors.initials: R
authors.lastname: Kaufman
authors.forename: D
authors.initials: D
authors.lastname: Sloley
mesh_terms: D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D004298:Dopamine / Q000378:metabolism*; D005260:Female; D008995:Monoamine Oxidase / Q000378:metabolism*; D011817:Rabbits; D012701:Serotonin / Q000378:metabolism*; D013987:Ticks / Q000201:enzymology*
chemical_list: D015102:3,4-Dihydroxyphenylacetic Acid; D012701:Serotonin; D008995:Monoamine Oxidase; D004298:Dopamine