Evaluation of Exposure to Water Aerosol or Air by Nose-Only or Whole-Body Inhalation Procedures for CD-1 Mice in Developmental Toxicity Studies

Abstract

Evaluation of Exposure to Water Aerosol or Air by Nose-Only or Whole-Body Inhalation Procedures for CD-1 Mice in Developmental Toxicity Studies. Tyl, R. W., Ballantyne, B., Fisher, L. C., Fait, D. L., Savine, T. A., Pritts, I. M., and Dodd, D. E. (1994). Fundam. Appl. Toxicol. 23, 251-260. This study was performed to evaluate the effects of nose-only restraint versus whole-body exposure procedures in the absence of test chemical, and to determine the appropriate control environment (water aerosol or air) for subsequent developmental toxicity studies of test materials administered as aerosols. Timed-pregnant CD-1 mice, 30/group, were exposed to high concentrations of water aerosol or to air by whole-body or nose-only inhalation procedures on Gestational Days (GD) 6 through 15 for 6 hr per day. The group exposed to air by whole-body procedures was designated as the control group. Clinical observations and maternal body weights were recorded throughout gestation. At scheduled necropsy on GD 18, maternal animals were evaluated for body weight, gravid uterine weight, liver weight, number of ovarian corpora lutea, and status of uterine implantation sites. Fetuses were counted, weighed, and sexed and were examined for external, visceral (including craniofacial), and skeletal alterations. Indices of maternal toxicity were affected in both nose-only groups. Maternal body weights were reduced during and after the exposure period; maternal weight gain was reduced during the exposure period. Clinical signs observed, from animals struggling during restraint, were resolved by GD 18. At sacrifice on GD 18, maternal body weights and maternal gestational weight gains (both corrected for gravid uterine weights) and absolute liver weights were reduced in both nose-only groups. Four females died (13.3%, all pregnant) in the air nose-only group, and maternal liver weight (relative to body weight) was reduced in the aerosol nose-only group. Gestational parameters were unaffected by any of the treatments. There were no statistically significant differences in the incidences of any individual malformations or malformations by category (external, visceral, or skeletal) or of total malformations. However, exencephaly, low set ears, cleft palate, and ventricular septal defect were observed only in both aerosol-exposed groups (whole-body and nose-only exposed). The incidences of individual external or visceral variations or of variations by category or of total variations were unaffected. The incidence of one skeletal variation, poorly ossified supraoccipital skull bone, was significantly increased in the aerosol nose-only group relative to the air whole-body controls. There were also increased incidences (not statistically significant) of extra (14th) ribs in both aerosol groups. Therefore, maternal restraint (in both nose-only groups) during organogenesis produced indications of maternal toxicity, but restraint did not appear to affect normal embryo/fetal morphologic development. Maternal exposure to water aerosol (by whole-body or nose-only procedures) resulted in small, biologically significant (but not statistically significant) increases in the incidences of fetal malformations and variations. In conclusion, for mice at least, nose-only exposures employing the present procedures can be used effectively, and water aerosol is an appropriate control environment for developmental toxicity studies of test materials administered as aerosols at high concentrations.