Specificity of the effects of lead on brain energy metabolism for substrates donating a cytoplasmic reducing equivalent.

Lead chloride, at concentrations of 67 muM in the incubation media, inhibits the potassium-stimulated respiration (3 to 30mM increase in K+) of rat cerebral cortex slices. The inhibition observed was dependent upon the substrate provided. In the presence of 10mM glucose or lactate, 35-50% inhibition of the response was observed, but no evidence of an effect could be observed when 10mM pyruvate served as substrate. In consonance with these observations, spectral measurements during the course of the response revealed an attenuation of the initial NAD(P)H oxidation followed by a substantial accumulation of the intermediate in slices metabolizing glucose, but not those metabolizing pyruvate. In vivo treatment of adult rats with six intrapertoneal injections spaced over a 14-day period gave rise to essentially similar findings at cerebral cortical lead concentrations averaging 0.41 mug/g (range equals 0.34-0.52) and above. No effect was observed at brain lead concentrations averaging 0.17 mug/g. These data suggested that lead interfered with the oxidation of the NAD(P)H produced by the initial oxidations of glucose in the cytoplasm. Inhibition of cytoplasmic NAD(P)H oxidation by brain mitochondria is of peculiar importance in a tissue relying almost exclusively upon the metabolism of glucose in vitro.