Embryonic blastemic changes in retinoic acid-induced hindlimb deformity.

In this study we analyzed, on an experimental model, blastemic changes occurring during the embryonic period that may later cause fetal hindlimb deformity. Experimental induction of clubfoot-like deformity in rat fetuses was performed by maternal administration of retinoic acid (RA) (120 mg/kg body weight) as a single intragastric dose on day 10 of pregnancy (previous phase of this assay). The caudal and hindlimb blastemic changes were studied by mitosis count and stereological, immunohistochemistry and AgNOR techniques in the hindlimbs of 15-day embryos and in the caudal somites of 11-day embryos. In 15-day embryos from the assay group, hypoplasia and misorientation of hindlimbs were present in 90% of the cases. The histological study showed a blastemal defect as follows: (a) reduction in mesenchymal cell activity (mitotic and AgNOR activities); (b) increase of volume of vascular lumen; (c) reduction in volume of nerve structures, and (d) reduction in the percentage of pre-rhabdomyoblastic cells. In 11-day embryos from the assay group, caudal somites showed disruption, including loss of usual morphology. Moreover, somitic AgNOR activity decreased compared to the control group. The greatest reduction in the number of black-dots per cell was in the myotome. These findings suggest that a certain pathology of the somites, very little studied to date, might be involved in clubfoot pathogenesis.