Toxicology Letters 93 (1997) 205 – 213 Hydroquinone increases the frequency of micronuclei in a dose-dependent manner in mouse bone marrow G.C. Jagetia *, R. Aruna Department of Radiobiology, Kasturba Medical College, Manipal 576 119, India Received 24 June 1997; received in revised form 6 October 1997; accepted 6 October 1997 Abstract The frequency of micronuclei (micronucleated polychromatic erythrocytes, MPCE and micronucleated normochro- matic erythrocytes, MNCE) was studied at 12, 24 and 36 h post-treatment in the bone marrow of mice treated with 0, 0.78, 1.56, 3.125, 6.25, 12.5, 25, 50, 75 and 100 mg/kg body wt of hydroquinone (HQ). Treatment of mice with various doses of HQ resulted in a dose dependent increase in the frequency of both MPCE and MNCE at all the post-treatment time periods. The frequency of MPCE was significantly higher after administration of 3.125 mg/kg HQ at 24 h post-treatment, except 12 and 36 h, where a significant increase in the frequency of MPCE was observed only after administration of 6.25 mg/kg drug dose. Similarly, a significant increase in the frequency of MNCE was observed after 12.5 mg/kg HQ treatment at all the post-treatment time periods. The dose effect relationship between various HQ doses and MPCE and MNCE induction was linear and linear quadratic, respectively at all the post-treatment time periods. The PCE/NCE ratio declined in a dose dependent manner at all the post-treatment time periods and this decline was significant when compared to non-drug treated controls. The dose effect relationship was linear quadratic at all the post-treatment time periods studied. © 1997 Elsevier Science Ireland Ltd. Keywords: Hydroquinone; Mouse; Bone marrow; Micronuclei; PCE/NCE ratio 1. Introduction In man many cancers result from environmen- tal carcinogens (Boyland et al., 1967; Higginson et al., 1969) in addition to occupational hazard re- lated neoplasia. Hydroquinone (HQ) is found in both free and conjugated forms in plants and animals (Ho ¨ gl et al., 1958; Eisner et al., 1958; Howard et al., 1979; Iguchi et al., 1990). Indus- trial production also adds to the environmental burden of HQ. HQ is widely used as an antioxi- dant or stabilizer for certain materials that poly- merize in the presence of free radicals, and as a chemical intermediate for the production of anti- * Corresponding author. Tel.: +91 8252 712007/71219, ext.: 2122; fax: +91 8252 70062. 0378-4274/97/$17.00 © 1997 Elsevier Science Ireland Ltd. All rights reserved. PII S0378-4274(97)00093-3