Sites of lead localization in embryonic chick tissues following treatment

Lead treatment by subgerminal injection causes rupture of embryonic chick dorsal aortae during early morphogenesis, followed by localized caudal hematoma formation. Shortly thereafter, damaged tissues are resorbed, leading to a condition known as rumplessness (caudal dysplasia syndrome in humans). We have studied this process by light microscopy and have found that the caudal dorsal aortae exhibit morphological alterations as early as 4 hr after injection. Further, we used energy dispersive X-ray analysis (EDXA) to establish the precise localization and distribution of lead in the developing embryo, 4 hr after Pb(NO3)2 treatment. Embryos treated with NaNO3 were used as controls. The hierarchy of lead concentrations was endothelium of the caudal dorsal aortae greater than caudal endoderm greater than blood cells. The surrounding mesenchyme, neural tube, and notocord, as well as all control embryonic tissue, exhibited no detectable lead levels. These results suggest that lead has a high degree of specificity for entering and damaging the developing caudal dorsal aortae. A possible mechanism for this phenomenon is that lead gains access to the vascular net surrounding the caudal region of the embryo at the time of injection. Parts of this vascular net including the lead are then incorporated into the developing caudal dorsal aortae as they grow distally, thus further concentrating the lead.