C Pharmacology & Toxicology 2003, 92, 148–152. Copyright C Printed in Denmark . All rights reserved ISSN 0901-9928 Toluene Depresses Plasma Corticosterone in Pregnant Rats Karin S. Hougaard 1 , Åse M. Hansen 1 , Ulla Hass 2 and Søren P. Lund 1 1 National Institute of Occupational Health, DK-2100 Copenhagen Ø, and 2 Danish Veterinary and Food Administration, DK-2860 Mørkhøj, Denmark (Received April 4, 2002; Accepted December 19, 2002) Abstract: Combined exposure to stressors and chemicals may result in synergistic effects. The effects of prenatal exposure to the organic solvent toluene resemble those observed in offspring of gestationally stressed dams, a possible common mechanism being transfer of stress-/toluene-induced increments of corticosteroids from the maternal to the foetal compart- ment. Pregnant rats were subjected to either 1500 ppm toluene 6 hr/day and/or a schedule of ‘‘Chronic mild stress’’ during the last two weeks of gestation. Exposure to toluene was associated with reduced birth weight and lower maternal weight gain, the latter being enhanced by maternal stress. A depressant effect of toluene on maternal corticosterone was observed, hence the study does not provide immediate evidence that transfer of elevated levels of corticosterone from the maternal to the foetal compartment mediates the effects of prenatal exposure to toluene. Several chemicals, including organic solvents, are able to activate the hypothalamic-pituitary-adrenal axis as indi- cated by elevated levels of e.g. corticosterone and adreneno- corticotropic hormone in blood (Cameron et al. 1985; Weinberg & Bezio 1987; De Boer et al. 1988; Pruett et al. 1993; Murakami et al. 1997; Imai et al. 1998). Toluene is one of the most frequently used aromatic solvents in Denmark (Simonsen et al. 1995). The effect of toluene on the hypothalamic-pituitary-adrenal-axis has been investi- gated in rodents, but findings are inconsistent as some studies show enhanced secretion of corticosterone (Anders- son et al. 1980; Hsieh et al. 1991; Little et al. 1998), whereas others found no changes (Andersson et al. 1980 & 1983; Howell et al. 1986; von Euler et al. 1988 & 1991). This may be due to differences in experimental designs with respect to exposure periods (3 days-32 weeks), times of measure- ment in relation to exposure, and dose levels (80–10,000 ppm inhalation). None of these investigations were per- formed in female non-pregnant and pregnant animals. Regarding human health and toluene, a major area of concern relates to pregnancy as prenatal exposure to tolu- ene has been shown to affect foetal development. Thus, lower birth weight and delayed postnatal development have been reported in a number of studies (reviewed in Øster- gaard 2000). Also, cognitive function was found to be im- paired in offspring prenatally exposed to toluene, when evaluated in the Morris water maze (Hass et al. 1999; Hou- gaard et al. 1999). The effects observed after prenatal ex- posure to toluene resemble those observed in offspring of gestationally stressed dams (Weinstock et al. 1988; Hass et al. 1999; Hougaard et al. 1999; Weinstock 2001). One pro- posed mechanism underlying the postnatal effects observed Author for correspondence: Karin S. Hougaard, Department of Chemical Work Environment, National Institute of Occupational Health, Lersø Parkalle ´ 105, DK-2100 Copenhagen Ø, Denmark (fax π45 39 16 52 01, e-mail ksh/ami.dk). after prenatal stress relates to transfer of stress-induced el- evated levels of corticosteroids from the maternal to the foetal compartment, as corticosteroids quickly traverse the placenta (Weinstock 1997; Williams et al. 1999; Ghosh et al. 2000). Bearing the observations of chemical activation of the hypothalamic-pituitary-adrenal-axis in mind, it has been hypothesized that some chemicals, in addition to di- rect biochemical effects, exert effects via stress-like changes in maternal physiology (Chernoff et al. 1987; Pruett et al. 1993). The purpose of the present study was to investigate the effects of toluene on concentrations of corticosterone in plasma from pregnant rats. Further, the interaction between toluene and stress was investigated in two groups of preg- nant rats, one stressed group and one group exposed to both stress and toluene. Traditional maternal and birth par- ameters were included as measures of the effect of exposure on the course of pregnancy (EPA 1991). Materials and Methods Sixty-four time-mated young adult nulliparous rats (Mol: WIST) arrived at gestation day 4 and were pair-housed in plastic cages with bedding under controlled environmental conditions with lights from 7 p.m. to 7 a.m. (Hougaard et al. 1999). Animals were 1) controls or exposed to 2) ‘‘Chronic mild stress’’ during gestation day 9–20, 3) 1500 ppm toluene, 6 hr/day on gestation day 7–20 or 4) exposed to both. The dose level and exposure periods were chosen as to avoid marked maternal or foetal toxicity based on previous studies (Hass et al. 1999; Hougaard et al. 1999). Exposure was performed in whole-body exposure chambers under previously described con- ditions, although, in addition to tap water, new food pellets for one day were supplied every day (Hass et al. 1999; Hougaard et al. 1999). Preceding the daily chamber exposure, all dams were trans- ferred to wire cages with their partner. They were returned to their plastic cages less than one hour after the end of exposure. Toluene was only led into chambers holding the toluene and the combined exposure groups. The mean concentration after reaching equilib- rium in the exposure chambers was 1504∫23 (S.D.) ppm toluene. The schedule of ‘‘Chronic mild stress’’ was based on the principles