1 A time-course study was carried out in mice subchroni cally exposed to As III (as sodium arsenite) or As V (as sodium arsenate), via drinking water, relating the pattern of urinary porphyrin excretion to the renal and hepatic enzyme activities of porphobilinogen deaminase (PBGD), uroporphyrinogen III synthetase (URO III-S), uropor phyrinogen decarboxylase (URO-D) and coproporphyrino gen oxidase (COPRO-O), as well as to the hepatic por phyrin accumulation in the treated animals.
2 A time-dependent, wave-like porphyric response was found in mice exposed to As V, and the increases seen in total urinary porphyrins (at 3 weeks of exposure) corre sponded to an increased activity of PBGD and Uro III-S in liver.
3 Significant decreases in renal URO-D and hepatic and renal COPRO-O activities were found in treated mice; these inhibitions were more pronounced in animals exposed to As III.
4 The combination of these enzymic effects may explain the time-dependent porphyric response of mice subchroni cally exposed to As. Finally, the relative magnitudes of URO-D and COPRO-O inhibitions may determine the pat tern of porphyrin concentration observed in urine and tis sues.
5 The decrease in renal URO-D activity may help to explain the inversion in the coproporphyrin/uroporphyrin ratio previously reported in humans chronically exposed to As; however, there were differences between the uri nary porphyrin profiles found in both species. The possi ble reasons for the similarities and differences are briefly discussed.
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