LEAD: TOXICITY AND TISSUE LEVELS IN THE EMBRYO

Abstract

Lead (Pb) injected into yolk sacs of day 4 chick embryos results in progressive central nervous system(CNS) bleeding which subsides by day 10-12 and is followed by the development of hydrocephalus. The use of Pb 210 permitted a correlation between the dose of Pb, tissue Pb levels, morbidity, and mortality. Increasing the Pb dose resulted in increasing CNS damage, mortality, and increasing concentrations of total body, blood and brain Pb. Injection of Pb after day 11 was accompanied by a marked decrease in morbidity and mortality. This was associated with reduced brain Pb concentrations, but no decrease in blood Pb levels. This indicates the development of a blood-brain barrier to Pb at this period in development and corresponds to the formation of specialized endothelial junctions in the CNS. Administration of Ca Edta at intervals after Pb injection on day 4 enabled delineation of the minimum period required for the occurrence of Pb toxicity. Edta given 2 minutes after Pb resulted in complete protection against Pb induced CHS damage and mortality. At intervals up to 8 hours there was a substantial diminution in morbidity and mortality. At longer intervals little protection was afforded by Edta. Blood and body Pb levels remained unchanged, irrespective of Edta administration; however, brain Pb levels increased with increasing Pb-Edta intervals. These results demonstrate a relationship between CNS damage and brain Pb levels and indicate that a brief exposure to Pb early in development suffices to produce CNS damage and embryo death.

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