Distinct Enzymatic Responses in Mice Exposed to a Range of Low Doses of Ozone

Abstract

Short-term exposure of mice to low 03 doses, as defined by the product of concentration and exposure time (ct), was observed to induce alterations in two enzyme systems: first, that leading to changes in hepatic reduced ascorbic acid (RAA) content, and second to changes in plasma creatine phosphokinase (CPK) activity. RAA alterations were noticed immediately, 30 min and 120 min after termination of the exposure period, whereas CPK showed alterations immediately and 15 min after termination of the exposure. Later determinations, i.e., 24 hr after 03 exposure for RAA and 30 min after 03 exposure for CPK, revealed no significant differences when compared to control animals. Although differences in sensitivity existed, the dose response curves for both systems were more or less similar, showing a short decrease for the initial very low 03 doses, followed by a profound rise and a gradual decrease to control levels for subsequent ct doses. Exceptions were the 30 min curve for RAA and the immediate curve for CPK in so far as that both showed an additional depression.Neither plasma histamine nor plasma lactic acid dehydrogenase (LDH3) were observed to be altered by the range of 03 doses employed. These findings were explained on the basis of adaptation of the organism to a potentially noxious 03 stimulus by enhanced metabolic processes: a weak stimulus leading to only a small adjustment, and stronger stimuli to elevated enzyme activity as well. With increasing doses of 03 this elevation in enzyme activity was found to be gradually diminished, possibly due to a steadily growing demand, leaving the overshoot becoming continually smaller until a balanced state is achieved.Radiomimetic activity of ozone (03), first described by Brinkman and Lamberst (1) (5, 6). In the opinion of these authors there is no threshold value (no-effect level), and the dose-effect curve starts at zero. However, in the same way as with ionizing irradiation, in order to visualize effects, dosages of 03 have to be explored which in general clearly exceed the permissible