Several compounds structurally related to IVh were examined for their ability to cross-react with the antiserum obtained, i ~. . their ability to displace radiolaheled IVb from antibody binding sites. Antibodies were unahle to distmguish among IVh, 1. and the structurally siniilar ergot alkaloids ergonovine and methqlergonovinc. Frgotamine also exhibited cross-reactivity. but at approximately ICfold higher concentrations. The following indoles did not exhihit any ability to displace radiolabelcd IVh from antibody binding sites at concentrations of at least 10 mcg./ml. of incubation mixture: tryptamine. iV-methyltryptaniine. j-inethoxydiiiiethyltryptamine. 5-hydroxytryptophan. and 5-hydroxqtryptamine (serotonin). No exhaustive study of cross-reactivity was completed ; howevei , these results compare in genrral with thosc reported hy Vunakis ct ul. (4). Judging from information supplied in a commercial kit1, antiserum produced by other methods may exhihit somewhat greater specificity. One outstanding example appears to be that these authors report little cross-reactivity with I at concentration levels similar to 1Vh. while thcse two compounds appear essentially indistingtdiable using our antiscrtun.
SUhlhlARY
A quick and convenient radioimmuiioassay system was developed for the quantitative determinatlon of lysergide (IVh) in drug products. human plasma. serum. or urine at levels as low as 1 ng. or for its qualitative detection at picogram levels. Liter quantities of antiserum were obtained since sheep were employed for the production of antibodies. An advantage of the method is in its utilimtion of commercially available tritiated IVh; however, the low specifc activity of this material also places a limit upon the sensitivity. The method also has the advantage of not requiring a second antibody technique for the separation of free and bound I V b but is based upon adsorption of free IVb to dcxtran-coated charcoal. Current cl'forts are directed toward the acquisitioii of IVh of higher specific activity and the devclopnient of methods utilizing immohiliied antibock< for cnicientlb concentrating 1Vh i n biological samples 50 that the quantitative assay may be extended to the picogram levels required in the study of the absorption, distribution, metabolism, andexcretion of IVD. However, even in its current state the method promises to be of considerable utility in the assay of illicit drug saniples and in animal investigations where large1 quantities of lyseryide 1Vb are employed.
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