Measurement of HPRT mutations in splenic lymphocytes and haemoglobin adducts in erythrocytes of Lewis rats exposed to ethylene oxide

Young adult male Lewis rats were exposed to ethylene oxide (EO) via single intraperitoneal (i.p.) injections (10-80 mg kg(-1)) or drinking water (4 we eks at concentrations of 2, 5, and 10 mM) or inhalation (50, 100 or 200 ppm for 4 weeks, 5 days week(-1), 6 h day(-1)) to measure induction of HPRT mu tations in lymphocytes from spleen by means of a cloning assay. N-ethyl-N-n itrosourea (ENU) and N-(2-hydroxyethyl)-N-nitrosourea (HOENU) were used as positive controls. Levels of N-(2-hydroxyethyl)valine (HOEtVal) adducts in haemoglobin (expressed in nmol g-l globin) were measured to determine blood doses of EO (mmol kg(-1) h, mM h). Blood doses were used as a common denom inator for comparison of mutagenic effects of EO administered via the three routes. The mean HPRT mutant frequency (MF) of the historical control was 4.3 X 10(-6). Maximal mean MFs for ENU(100 mg kg(-1)) and HOENU (75 mg kg(- 1)) were 243 X 10(-6) and 93 X 10(-6), respectively. In two independent exp eriments. EO injections led to a statistically significant dose-dependent i nduction of mutations, with a maximal increase in MF by 2.3-fold over the b ackground. Administration of EO via drinking water gave statistically signi ficant increases of MFs in two independent experiments. Effects were, at mo st, 2.5-fold above the concurrent control. Finally, inhalation exposure als o caused a statistically significant maximal increase in MF by 1.4-fold ove r the background. Plotting of mutagenicity data (i.e., selected data pertai ning to expression times where maximal mutagenic effects were found) for th e three exposure routes against blood dose as common denominator indicated that, at equal blood doses, acute i.p, exposure led to higher observed MFs than drinking water treatment, which was more mutagenic than exposure via i nhalation. In the injection experiments, there was evidence for a saturatio n of detoxification processes at the highest doses. This was not seen after subchronic administration of EO. The resulting HPRT mutagenicity data sugg est that EO is a relatively weak mutagen in T-lymphocytes of rats following exposure(s) by i.p. injection, in drinking water or by inhalation. (C) 199 9 Elsevier Science B.V. All rights reserved.