Postnatal evolution of supernumerary ribs in rats after a single administration of sodium salicylate

Radiographs were used to follow the postnatal evolution of 14th ribs in rat pups, Initially, 30 pregnant female rats were randomly distributed into tw o groups receiving 0 or 300 mg kg(-1) sodium salicylate on day 9 of pregnan cy. In the treated group, adverse effects were noted on body weight changes and food consumption during the 2 days following dosing. At birth, a high majority of pups had extra ribs at the 300 mg kg(-1) dose. Radiographs done on postnatal days 1, 6, 14, 28 and 54 showed a reduction in the incidence of rudimentary ribs only, whereas extra ribs, often associated with 27 pres acral vertebrae, had the same incidence from birth to adult stage. Furtherm ore, extra ribs seemed to exhibit similar growth evolution to the other tho racic ribs. This work helps to clarify the postnatal evolution of supernume rary ribs because it was performed on the same animals from birth to adult stage, showing that the reversibility was related to rib length and, in con sequence, concerned the rudimentary ribs only, The coexistence of additiona l presacral vertebrae primarily with extra ribs suggests that both kinds of supernumerary ribs (rudimentary and extra) might be different phenomena an d could be considered separately in developmental toxicology studies. Copyr ight (C) 2000 John Wiley & Sons, Ltd.