Effects of lead inhalation exposures alone and in combination with carbon monoxide in nonpregnant and pregnant rats and fetuses. II. Effects on delta-aminolevulinic acid dehydratase activity, hematocrit and body weight.

Pregnant and nonpregnant rats were exposed for 21 days to an aerosol containing 1, 3 and 10 mg lead/m3 air and to a combination of 3 mg Pb/m3 and 500 ppm carbon monoxide (CO). Pregnant and nonpregnant rats exposed to uncontaminated air served as controls. The activity of the fetal delta-aminolevulinic acid dehydratase (ALA-D) was less inhibited by lead than the maternal activity. Furthermore, the degree of inhibition was highly reduced in the fetuses by additional CO-inhalation, whereas in adult animals the depression of the ALA-D was accentuated by additional CO-inhalation in accordance with epidemiological data. Therefore, it is concluded that the mode of plumbic inhibition of the ALA-D activity differs in fetuses from that in adults. Furthermore, the adaptation to the inhibition of the ALA-D by de novo synthesis of this enzyme was less in fetuses than in adult rats. The high lead aerosol concentration reduced hematocrit and body weight of the fetuses, but it did not influence these parameters in adult rats, thus pointing to a higher lead-sensitivity of the fetal than the adult organism. A stronger inhibition of maternal ALA-D activity than of the activity of nonpregnant animals possibly indicates a higher susceptibility to lead in pregnancy.