Neonatal phenobarbital imprinting of rat hepatic microsomal testosterone hydroxylations.

The effects of neonatally administered phenobarbital (PB) on adult rat hepatic microsomal metabolism of testosterone were examined in 60-, 90-, and 120-day-old animals. Phenobarbital-induced imprinting was evident at all ages; however, female rats appeared to be more susceptible to the neonatal effects of phenobarbital than did male rats. In 60-day-old female rats, increased testosterone 2 alpha-hydroxylase activity was observed in microsomes from noninduced rats, whereas decreased testosterone oxidation at all positions except 2 alpha and 15 beta was observed in microsomes from Aroclor 1254-induced rats. The decreased oxidation of testosterone at specific sites in response to Aroclor 1254 induction was quite dramatic, decreasing the activities to near or below control levels. By contrast, phenobarbital-treated 60-day-old males exhibited approximately a twofold increase in Aroclor 1254-induced 16 alpha and 2 alpha-hydroxylase activities. The pattern of changes in testosterone metabolism observed in phenobarbital-treated animals was different at both 90 and 120 days from that at 60 days. Only minor alterations in the oxidation of testosterone were observed in 90-day-old animals of either sex. In 120-day-old animals the greatest effects of neonatal phenobarbital exposure were on Aroclor 1254-induced 16 beta-hydroxylase activities. In induced female rats 16 beta-hydroxylase activity was again decreased to noninduced levels, while in induced male rats a fourfold increase in this activity was observed. The results demonstrate that neonatal exposure to phenobarbital can alter both constitutive and Aroclor 1254-induced testosterone metabolism in adult rats and that the effects of neonatal phenobarbital exposure are age and sex differentiated.

Aroclor 1254 as an antagonist of the teratogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin.

Administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 20 micrograms/kg) to pregnant C57BL/6J mice (on day 10) resulted in 62% fetuses with cleft palate per litter without any observable maternal toxicity. In contrast, Aroclor 1254 administered at a dose of 750 mumol/kg was not teratogenic. Cotreatment of the pregnant mice with both Aroclor 1254 (244 mg/kg) and 2,3,7,8-TCDD (20 micrograms/kg) resulted in an 8.2% incidence of cleft palate per litter. In contrast, Aroclor 1254 did not afford any protection from the teratogenicity of dexamethasone in C57BL/6J mice. Previous studies have shown that Aroclor 1254 can act as a partial antagonist of the microsomal enzyme induction and immunotoxic effects of 2,3,7,8-TCDD in C57BL/6J mice and this paper demonstrates that the commercial polychlorinated biphenyl mixture also antagonizes 2,3,7,8-TCDD-mediated teratogenicity in this strain of mice.

The effects of organochlorine pesticides as inducers of testosterone and benzo[a]pyrene hydroxylases.

p,p'-DDE, phenobarbital, dieldrin heptachlor, chlordane and toxaphene induced rat liver microsomes exhibited increased formation of the 4,5-dihydrodiol, 3,6-quinone, 9- and 3-hydroxymetabolites of benzo[a]pyrene and the latter three compounds also induced an increase in the rate of formation of the 9,10-dihydrodiol metabolite. Lindane was inactive as an inducer of benzo[a]pyrene hydroxylase. With the exception of lindane, all the organochlorine pesticides and PB induced testosterone 16 alpha- and 16 beta-hydroxylases; in contrast lindane induced testosterone 6 alpha-, 7 alpha- and 6 beta-hydroxylases and PB also induced testosterone 15 beta-hydroxylase and androstenedione formation. Using a battery of monooxygenase enzyme assays it was evident that there were significant differences between PB and several organochlorine pesticides as inducers of rat hepatic cytochrome P-450-dependent monooxygenases.

The in vitro metabolism of benzo[a]pyrene by polychlorinated and polybrominated biphenyl induced rat hepatic microsomal monooxygenases.

The metabolism of benzo[a]pyrene by halogenated biphenyl-induced rat hepatic microsomal monooxygenases was determined using a high pressure liquid chromatographic assay system. Incubation of benzo[a]pyrene with microsomes from rats pretreated with phenobarbitone or phenobarbitone-type inducers (2,2',4,4',5,5'-hexachlorobiphenyl, 2,2',4,4',6,6'-hexachlorobiphenyl, 2,2',5,5'-tetrachlorobiphenyl, 2,2',4,4',5,5'-hexabromobiphenyl, and 2,2',5,5'-tetrabromobiphenyl) resulted in increased overall metabolism of the hydrocarbon (less than fourfold) into phenolic, quinone, and diol metabolites, with the most striking increase observed in the formation of 4,5-dihydro-4,5-dihydroxybenzo[a]pyrene. In contrast, the metabolism of benzo[a]pyrene by microsomes from rats induced with 3-methylcholanthrene or 3,3',4,4'-tetrachlorobiphenyl resulted in a greater than 10-fold increase in overall benzo[a]pyrene metabolism, with the largest increases observed in the formation of the trans-7,8- and -9,10-dihydrodiol metabolites of benzo[a]pyrene. However, in comparison to control and phenobarbitone-induced microsomes, the oxidative conversion of benzo[a]pyrene by microsomes induced with 3-methylcholanthrene and 3,3',4,4'-tetrachlorobiphenyl into the 6,12-quinone was substantially inhibited. Previous reports have shown that the commercial halogenated biphenyl mixtures, fireMaster BP-6, and Aroclor 1254 are mixed-type inducers and that microsomes from rats pretreated with these mixtures markedly enhance the overall metabolism of benzo[a]pyrene. Not surprisingly, the metabolism of benzo[a]pyrene by microsomes from rats pretreated with the mixed-type inducers, 2,3,3',4,4'-penta-,2,3,3',4,4',5-hexa-, and 2',3,3',4,4',5-hexa- chlorobiphenyl was also increased and the metabolic profile was similar to that observed with fireMaster BP-6 and Aroclor 1254 induced microsomes.