Regressive or lethal lead encephalopathy in the suckling rat. Correlation of lead levels and morphological findings.

Lead encephalopathy was produced in immature Sprague-Dawley rats with an intraperitoneal (IP) injection of 60 micrograms/g body weight of lead acetate administered daily from the fifth day after birth. Macroscopic and light microscopic study of the nervous system, estimations of the blood-brain barrier permeability to proteins and brain water content were performed every two days thereafter. Lead levels in total blood, plasma, and several brain areas were measured at the same intervals by flameless atomic absorption spectrometry. Electron microscopic study of the cerebellum was done 2, 6, and 12 days after beginning lead administration. After two days of lead administration and before any pathological change occurred the increase in lead level was greater in the cerebellum than in other brain areas. After four to six days, hemorrhagic lead encephalopathy developed and was most prominent in regions with higher lead levels. From day 11 to 14, there were two possible courses: a) improvement of the clinical status and morphological findings in 25% of the animals, or b) progression of abnormal clinical signs and death. Cerebral edema, both intra- and extracellular, may have contributed to the fatal evolution. The mechanism of this edema appeared complex and may have involved resorption failure. Good correlations were observed among progression of the clinical signs, high water content in the brain, morphological evidence of cerebral edema, and a high cerebellar lead level. In contrast, high blood lead levels could be associated with clinical improvement, normal brain water content, and regression of the pathological findings. These data suggest that differences in evolution are more likely related to differences in the development of resistance of the cerebral capillary to lead, or in the efflux of lead, rather than to the blood lead concentrations.