The Science of the Total Environment, 71 (1988) 547-550 547 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands HEATING REACTIVATION OF RATS AMINOLEVULINIC ACID DEHYDRATASE IN LEAD POISONING A. TREVISAN, M. RAIMONDI, A. BUNGARO and P. CHIESURA Istituto di Medicina del Lavoro Universit& di Padova Padova - Italy SUMMARY Heat reactivation (60°C for 5 minutes) of the red blood cells aminolevuli- nic acid dehydratase activity was studied in lead treated rats (0.25 to 5.0 mg/kg b.w., i.p., for 4 weeks). Complete enzyme reactivation occurs with lead blood concentration up to about 70 mcg/dl. At higher blood lead concentra- tions, only a part of the enzyme can be restored by heating. The different mechanisms of aminolevulinic aicd dehydratase activity inhibition by lead are discussed. INTRODUCTION Experiments in man (refs.l-6) and animals (ref.3) exposed to lead show that heat treatment (60°C for 5 minutes) of hemolyzed blood reactivates completely erythrocyte aminolevulinic acid dehydratase (ALA D, E.C. 4.2.1.24). The hypothesis was, therefore, that the enzyme is inhibited by a thermo- labile factor (ref.l), which is either activated or synthetized after lead ex- posure. This factor is induced early after lead exposure (re f.7). Gel-filtra- tion of the erythrocyte supernatant elutes the factor with hemoglobin fractions (ref.8). It is unknown whether the heat effect on human ALA D depends on blood lead concentration. The aim of the present paper is to measure heat reactivation of ALA D activity at different blood lead concentrations. METHODS Forty-eight albino, male, Wistar rats (S. Morini, S. Polo d'Enza, RE, Italy), starting weight of 200 ~ i0 grams, were subdivided into 6 groups of 8 rats each. One group was considered as the control, the other 5 groups were treated i.p. with Pb(NO3) 2 (C. Erba, Milano, Italy) at doses of 0.25, 0.5, 1.0, 2.5 and 5.0 mg/kg b.w. dissolved in deionized water (0.5 ml volume) for 4 weeks, once a day (5 days a week), respectively. 24 hours after the last administration, blood samples were taken from the heart under ether anesthesia. The rats were fasted overnight. 0048-9697/88/$03.50 © 1988 Elsevier Science Publishers B.V.