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Main Title Significance of Supernumerary Ribs in Rodent Developmental Toxicity Studies: Postnatal Persistence in Rats and Mice.
Author Chernoff, N. ; Rogers, J. M. ; Turner, C. I. ; Francis, B. M. ;
CORP Author Health Effects Research Lab., Research Triangle Park, NC. Developmental Toxicology Div. ;NSI Technology Services Corp., Research Triangle Park, NC.
Publisher c1991
Year Published 1991
Report Number EPA/600/J-91/267;
Stock Number PB92-113299
Additional Subjects Teratogenic compounds ; Rats ; Mice ; Species specificity ; Fetus ; Reprints ; Supernumerary ribs ; Bromoxynil
Library Call Number Additional Info Location Last
NTIS  PB92-113299 Some EPA libraries have a fiche copy filed under the call number shown. 07/26/2022
Collation 8p
Pregnant Sprague-Dawley rats and Swiss-Webster mice were gavaged with bromoxynil at 15 and 96.4 mg/kg/day, respectively, on Days 6-15 of gestation. The frequency of supernumerary ribs (SNR), which are here defined as any degree of ossification lateral to the first lumbar vertebrae, was determined in fetuses at term and offspring on Postnatal Days 6, 20, and 40. Bromoxynil induced significant increases in the incidence of SNR in fetuses of both species. In rats, SNR occurred in 62% of treated fetuses as compared to 14% in controls; in mice these values were 45% and 11%, respectively. The postnatal incidence and persistence of SNR was species dependent. In the rat, postnatal SNR incidence in treated animals did not differ significantly from controls. In contrast, in mice the bromoxynil-induced elevated incidence of SNR persisted through Day 40 (42.3% in treated vs 0% in controls). Analysis of SNR was also done on the basis of their length (greater or less than 1/2 the length of the 13th rib). In the mouse, the incidence of smaller SNR was much lower on Day 40 as compared to Day 20; in contrast the incidence of larger SNR persisted through Day 40. In the rat, the incidence of larger SNR was too small to draw conclusions as to the postnatal fate of these structures. As in the mouse, however, the incidence of smaller SNR was significantly lower by Day 40. The significance of SNR in developmental toxicity remains problematic. (Copyright (c) 1991 by the Society of Toxicology.)