Morphological alterations in the developing fetal rat limb due to maternal injection of chlorambucil

On day 14 of pregnancy, rats were injected i.p. with 9.5 mg/kg of chlorambucil. At term, all the fetuses were stunted and had obvious skeletal malformations. From days 15-20 of gestation there was a steady progression of cell death and histologic derangement in long bone formation. This began on day 15, the day following exposure to chlorambucil, with extensive cell death of chondroblasts in the long bone primordia. By day 16, dead or dying cells were located in the cartilage model and became associated with a higher than normal matrix to cell ratio. In day 17 limbs, many cells of the cartilage model were irregular in size and shape so that the normally precise cellular arrangement was lacking. On day 18, periosteal and enchondrial calcification was delayed and scanty. The fibular hemimelia observed in all drug-treated term fetuses stained with alizarin appeared to result from lack of development of the proximal half of the cartilage model. The observed alterations, particularly bowing of the ulna, in the teratogen-treated fetuses appeared to result primarily from specific cell death and formation of aberrant cell types but abnormal cell products may also play a role.