Porter-Silber reaction

The Porter-Silber reaction, diagnostic for the dihydroxyacetone side-chain, depends upon prior Mattox rearrangement. " ... 

Ingestion of citrus fruits, coffee, carrots, and spinach have been reported to interfere with urinary assay of steroids by the Porter-Silber reaction (Bll). Citrus fruits also interfere with aldosterone assays, and corn and other vegetables are rich sources of nonsteroidal estrogen bio-assayable substances (Bll). 

The determination of 17-ketosteroids is most often determined in the clinical laboratory by the Zimmerman reaction, in which the ether-extracted material is allowed to react with m-nitroaniline to yield a colored product. Thus, any compound with the 17-keto basic structure such as reserpine, morphine, ascorbic acid, or their metabolites will interfere. The Porter-Silber reaction used in the determination of 17,21-dihydroxysteroids is also not specific, and the reaction requires a di-hydroxyacetone side chain. Paraldehyde, chloral hydrate, meprobromate, and potassium iodide have been found to interfere, and patients should be maintained free of these drugs for 24-48 hours before the urine collection (Bll). 

It has been found that triamcinolone [101] and the 21-phosphate esters [102] do not under go the Porter-Silber reaction. It was also shown that an increased sensitivity for this procedure can be obtained using the p-hydrazino-benzenesulfonic acid-phosphoric acid reagent [103],... 

Flydroxyzine may cause falsely elevated urinary concentrations of 17-hydroxycorticosteroids in certain lab tests (e.g., Porter-Silber reaction, Glenn-Nelson method)... 

Porter-Silber reaction. Porter and Silber found that steroids having the dihydroxy-acetone side chain at C, (I) read with phenylhydrazine in water-alcohol-sulfuric add to give a yellow product with an iibMorption maximum at 410 mit. The reaction is specific to the strticture (I) and Is usefUl for colorimetric detorminKlion of cortisone... 

Color reactions Boric acid (hydroxyquinones). Dimethylaminobenzaldehyde (pyrroles). Ferric chloride (enols, phenols). Haloform test. Phenylhydrazine (Porter-Silber reaction). Sulfoacetic acid (Liebermann-Burchard test). Tetranitromethane (unsaturation). Condensation catalysts /3-Alanine. Ammonium acetate (formate). Ammonium nitrate. Benzyltrimethylammonium chloride. Boric acid. Boron trilluoride. Calcium hydride. Cesium fluoride. Glycine. Ion-exchange resins. Lead oxide. Lithium amide. Mercuric cyanide. 3-Methyl-l-ethyl-2-phosphoiene-l-oxlde. 3-Methyl-1-phenyi-3-phoipholene-1-oxide. Oxalic acid. Perchloric acid. Piperidine. Potaiaium r-butoxIde. Potassium fluoride. Potassium... 

Other more or less specific but less important reagents are for unsaturated compoimds molybdoarsenate [111], tetranitromethane [111, 113], osmium tetroxide [111, 113), p-anfinodimethylaniline-SOg [111, 113] for phenols, the nitroso reaction (Boute reagent) and Feigl reagent [113] for o-diphenols, phloroglucinol and vanadic acid [113] for reactions of the side chain, the Porter-Silber reaction [111], methyl ketones and formaldehydogens [111] and further modified reactions usual in PC [129]. 

By the Porter-Silber reaction. This is the reaction o] certain corticosteroids with phenylhydrazine in th< presence of alcohol and sulphuric acid. 

This is a collective term for a group of corticosteroids which includes cortisol, cortisone, 11-deoxycortisol and their tetrahydro derivatives which are measured in plasma and urine by the Porter-Silber reaction. The term 17-hydroxysteroids is often used synonymously with 17-oxogenic steroids and to most intents and purposes they mean the same. However there is a subtle difference between the two in that 17-oxogenic steroids (determined by the Zimmermann reaction after reduction and oxidation) measures, in addition to the compounds mentioned above, cortol and cortolone. 

Altliough methods involving organic solvent extraction or protein precipitation wfil estimate both free and protein-bound cortisol in tlie circulation, immunoassay-based methods that determine cortisol directly from serum have essentially replaced all extraction-based methods for routine cortisol measurements save for urine free cortisol methods. Flistorically four general methods have been used for the quantitative estimation of total blood cortisol concentrations in the clinical laboratory. These are the Porter-Silber color reaction method modified for plasma,the use of sulfuric acid-induced fluorescence, HPLC methods, or immunoassay. In general, HPLC and immunoassay are now used in both clinical laboratories and reference laboratories for the quantitative determination of cortisol in serum or urine. 

Oxogenic steroids. These are urinary corticosteroids and their metabolites, measured by the Zimmermann reaction after borohydride reduction and bismuthate (or periodate) oxidation. Substances measured by this technique are similar to those measured by the Porter-Silber method with the addition of cortol and cortolone. 

The reaction of certain corticosteroids with phenylhydrazine in the presence of alcohol and sulphuric acid to give a yellow colour. Steroids which give this reaction have a dihydroxy-acetone side chain and they include such compounds as cortisol, 11-deoxycortisol, cortisone and their tetrahydro derivatives. Collectively they are known as 17-hydroxycorticosteroids (qv) or Porter-Silber chromogens. 

This method is specific for the 17,21-dihydroxy-20-keto corticosteroids (such as cortisone and hydrocortisone). The method depends upon the action of sulfuric acid with the 17,21-dihydroxy-20-keto groups to give rise to a glyoxal side chain. Subsequent condensation with phenylhydrazine yields a stable yellow color. This reaction was developed by Porter and Silber [98], and its mechanism was elucidated by Lewbart and Mattox [99] as follows ... 

Porter CC, Silber RH. A quantitative color reaction for cortisone and related 17,21-dihydroxy-20-ketosteroids. J Biol Chem 1950 185 201-7. 

Other methods for determining this group of steroids have been examined from time to time. These include colorimetric determination as dinitro-phenylhydrazones (Porter and Silber ) this has found application in biochemical work but is not suitable for determination of corticosteroids in pharmaceuticals, ( lark has described the reaction of corticosteroids... 

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