title: Effects of chronic arsenic exposure on hematopoietic function in adult mammalian liver.
abstract: In these studies the effects of ingested arsenic (As(+5)) on hepatic heme biosynthetic capability and hemoprotein function in adult male rats were investigated. Animals exposed for 6 weeks to 0, 20, 40, or 85 ppm sodium arsenate in the drinking water suffered depression of hepatic delta-aminolevulinic acid (ALA) synthetase and heme synthetase (ferrochelatase) activities, with maximal decreases to 67 and 55% of control levels, respectively, at 85 ppm. Concomitantly, urinary uroporphyrin levels were elevated by as much as 12 times, and coproporphyrin by as much as 9 times, control values. The rate of incorporation of (3)H-ALA into mitochondrial and microsomal hemes was depressed by 40-50% at 20 ppm but was increased with regard to controls by as much as 150% at the higher treatment levels. A similar biphasic pattern was observed in regard to (14)C-leucine incorporation into cellular membranal proteins. In contrast, the levels of ALA dehydratase, uroporphyrinogen I synthetase, aminopyrine demethylase, and cytochrome P-450 were not significantly changed in As(+5)-treated rats. These results support the hypothesis that chronic, low level, arsenic exposure results in selective inhibition of mitochondrial-bound heme biosynthetic pathway enzymes (ALA synthetase and heme synthetase) resulting in a substantial increase in urinary porphyrins, uniquely characterized by a greater increase in uroporphyrin than coproporphyrin levels. These changes occur independent of, or prior to, alterations in hepatic hemoprotein-dependent functions and may thus serve in the clinical analysis of pretoxic exposure to arsenic compounds in human populations.
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000378:metabolism; D000818:Animals; D001151:Arsenic / Q000494:pharmacology*; D020261:Arsenic Poisoning; D004781:Environmental Exposure; D005294:Ferrochelatase / Q000378:metabolism; D006410:Hematopoiesis / Q000187:drug effects*; D006418:Heme / Q000096:biosynthesis; D008099:Liver / Q000201:enzymology*; D008297:Male; D008862:Microsomes, Liver / Q000378:metabolism; D008930:Mitochondria, Liver / Q000378:metabolism; D011166:Porphyrins / Q000652:urine; D051381:Rats; D013997:Time Factors
chemical_list: D011166:Porphyrins; D006418:Heme; D000624:5-Aminolevulinate Synthetase; D005294:Ferrochelatase; D001151:Arsenic