title: Radioimmunoassay for etorphine in horses with a 125I analog of etorphine.
abstract: To improve the sensitivity and specificity of screening for etorphine in horses, an 125I-labeled etorphine analog was synthesized and an antibody to etorphine was raised in rabbits. A radioimmunoassay (RIA) for etorphine was developed, using these reagents. Bound and free 125I-labeled etorphine was separated by a double-antibody method that reduced interference from materials associated with equine urine. The 125I-labeled etorphine binding was rarely greater than 250 pg of background etorphine equivalents/ml in raw urine and was 100 pg/ml in hydrolyzed urine. The 125I-RIA was capable of detecting etorphine equivalents in urine above these background values. Etorphine equivalents were detected in equine urine samples for about 7 days after 4 mares were dosed with 0.22 microgram of etorphine/kg of body weight, IV. The stability of etorphine in urine from these mares was evaluated. Urine from these dosed mares was held in constant -20 C storage, and aliquots were repeatedly frozen and thawed. When analyzed for etorphine equivalents using an 125I-RIA, etorphine and its metabolites in urine samples were stable for less than or equal to 38 days if continuously frozen and also were resistant to repeated freezing and thawing.
authors.affiliation: Kentucky Equine Drug Testing and Research Program, Department of Veterinary Science, College of Pharmacy, University of Kentucky, Lexington 40546.
authors.forename: C L
authors.initials: CL
authors.lastname: Tai
authors.forename: C
authors.initials: C
authors.lastname: Wang
authors.forename: T J
authors.initials: TJ
authors.lastname: Weckman
authors.forename: M A
authors.initials: MA
authors.lastname: Popot
authors.forename: W E
authors.initials: WE
authors.lastname: Woods
authors.forename: J M
authors.initials: JM
authors.lastname: Yang
authors.forename: J
authors.initials: J
authors.lastname: Blake
authors.forename: H H
authors.initials: HH
authors.lastname: Tai
authors.forename: T
authors.initials: T
authors.lastname: Tobin
mesh_terms: D000818:Animals; D005048:Etorphine / Q000032:analysis* / Q000652:urine; D005260:Female; D006736:Horses / Q000652:urine*; D007457:Iodine Radioisotopes; D009019:Morphinans / Q000032:analysis*; D011863:Radioimmunoassay
chemical_list: D007457:Iodine Radioisotopes; D009019:Morphinans; D005048:Etorphine