SOFT - TIAFT 1998 Scientific Session 5 Thursday October 8, 1998
not available
Peter R. Stout and James A. Ruth

University of Colorado Health Sciences Center, Department of Molecular Toxicology and Environmental Health Sciences, 4200 East Ninth Avenue, Box C238, Denver, CO, 80262, USA

To investigate the mechanisms involved in the accumulation of drugs or other compounds into hair, we examined the deposition of two fluorescent dyes, rhodamine and fluoroscein in the hair of Balb/C (albino) mice and C57 (pigmented) mice. The deposition patterns of the two dyes were examined by fluorescence microscopy after systemic administration or external loading of each dye into untreated hair under varying conditions. This allowed for the direct comparison of the morphology of internal and external deposition of the same compound as well as a comparison of the deposition of a zwitterionic compound, rhodamine, and an anionic compound fluoroscein.

Twenty-three day old mice were administered rhodamine or fluoroscein i.p. on Wednesdays, Thursdays and Fridays for three weeks. One week after the final dose mice were sacrificed and hair harvested. An additional group was given one 10 mg/kg dose rhodamine or one 100 mg/kg dose of fluoroscein, sacrificed at 1, 2, 24 and 48 hours and skin and hair samples taken. One group of animals was co-administered rhodamine and fluoroscein. Untreated hair was soaked for 1, 5, or 12 hours in solutions of rhodamine or fluoroscein at 100 ug/ml or 1 ug/ml made up in pH 6, pH 9 and pH 3 buffers or methanol. Hairs were then washed briefly with water, dried and fixed on glass slides. After loading, aliquots of hair were washed by soaking in pH 6 phosphate buffer or methanol for 24 hours.

Bands corresponding to the dosage periods along the length of the hair were clearly evident for rhodamine deposited from the systemic circulation. Additionally the pattern of deposition appears to be within the internal protein matrix with little evident deposition in the surface of the hair. The intensity of the fluorescence was not affected by either phosphate buffer or methanol washes. Rhodamine appeared in the hair bulb within 1 hour of the dosing with significantly brighter fluorescence than the surrounding skin.

External loading of rhodamine into the hair resulted in staining of the junctions of cortical scales with nominal internal staining. This pattern persisted even after 12 hours of exposure to the loading solution. This fluorescence was not removed by pH 6 buffer or methanol wash. Fluoroscein followed a similar pattern with maximum fluorescence when loaded at pH 6 and nominal staining when loaded in pH 9 buffer or methanol. Marked diminution of fluorescence occurred after soaking in pH 6 buffer but not after soaking in methanol.

This work supported by NIH grant DA09545.

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