Additional endpoints and overview of a mouse skeletal variant assay for detecting exposure to teratogens

CD-1 mice were exposed in utero to one of 14 treatment regimes, several of them being replicated, with close agreement between series. Prenatal exposure to a teratogenic dose at a sensitive time enabled detection of 10 of 14 teratogen regimes by alterations in frequency or severity of a substantial number of the 88 variants in the Skeletal Variant Assay System (SVAS) screen when examined at 60-65 days post natal (DPN). These included 2,4,5-T (245T), Trifluralin (TFL), Maneb (MNB), Decamethrin (DMT), Acetazolamide (ACZM) either at 8 days post-coitus (DPC) or days 9-11 PC, trypan blue (TB), or 5' Bromodeoxyuridine (BUDR) on either 7 DPC, 8 DPC, or 9 DPC. Most of these observations have been reported elsewhere. All of the treatment regimes mentioned above, and another group of treatments, could be detected in the exposed CD-1 cohorts when additional endpoints were employed. One such endpoint was "frequently responding variants." These were: Interfrontals (IF), Parted Frontals (PF), Preoptic Sutures (PS), Foramina Transversaria Imperfecta of the first cervical (C) vertebra (FTI C1), FTI of the axis (C2), Accessory (Acc) Transverse Foramina (TF) of C3-C6, malformations of C3-C7, Fourteen (14) Ribs, Carpal Fusions (Fus), Lumbar Fus, 27-Presacral Vertebrae (PSV), and Sacral Fus. This endpoint revealed significant differences in the initial group of 10, plus Captan (CAPT) and Phenytoin (DPH). Yet another useful endpoint reported here was the existence of high magnitude effects (i.e., dramatic alterations in frequency of occurrence of a variant). These included IF in TB and ACZM; PF in ACZM; PS in BUDR; FTI-C1 in TB and 245T; FTI-C2 in 245T; 14 Ribs in ACZM, BUDR, and TFL; Carpal Fus in TB; 27-PSV in ACZM; Fewer than (<) 30 Caudal Vertebrae (Vert) in 245T, TFL; Caudal Fus in TB, ACZM-D9. Eight treatment regimes in all could be detected by the existence of 3 or more high magnitude effects (245T, MNB, TB, ACZM8, ACZM9-11, phenytoin, and possibly BUDR on days 7 or 8, each seen in one of two series only). Clusters of related variants were affected in 9 of the 14 groups: Frontal (F) bones and C Vert in 245T; F bones in ACZM-D8; Fus in Posterior Vert Column in ACZM-D9-11; C Vert and Fus in Vert and articular skeleton in TB; Thoracic (Th) Vert and rib-cage effects in BUDR.(ABSTRACT TRUNCATED AT 400 WORDS)