Phenol Red Excretion in Rats

Phenol red (= phenolsulfonphthalein) excretion is an indirect test for uricosuric activity. After intravenous injection phenol red is mainly eliminated by active secretion in the proximal tubulus of the kidney. Treatment with uricosuric agents decreases the secretory activity of tubulus cells resulting in a delayed excretion of phenol red. Plasma values of phenol red are increased in treated animals as compared to controls. 

Male Wistar rats weighing 120-150 g are treated orally with the test compound or the standard 30 min prior to intravenous injection via the tail vein with 2.5 ml/kg of a 3 % aqueous solution of phenolsul-fonphthalein. For intravenous application, 5.0 ml/kg of the test drug solution are injected immediately after the phenolsulfonphthalein injection followed by flushing with 2.5 ml/kg saline. By retro-orbital puncture blood samples are withdrawn after 30, 60 and 180 min. Blood (0.2 ml) is diluted with 2 ml 

9 % NaCl-solution and centrifuged. To 1 ml of the supernatant 1 ml of 1 % sodium carbonate solution and 8 ml of saline are added. Using a spectrophotometer (Eppendorf, Hamburg) extinction at 546 nm is determined. 

Extinction values are calculated for total blood. At each time interval the values in treated rats are compared statistically with those of controls. 

Kreppel E (1959) Der EinfluB einiger Phenylbutazonderivate auf den Phenolrotblutspiegel der Ratte. Med Exp 1 285-289 Scarborough HC, McKinney GR (1962) Potential uricosuric agents derived from 1,3-diphenyl-barbituric acid. J Med Pharm Chem 5 175-183 

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