Phenobarbital hormonal effects

To understand the MOA by which the thyroid tumors are produced, the effect of pyrethrins on rat thyroid gland, thyroid hormone levels, and hepatic thyroxine UDP-glucuronosyltransferase activity was also investigated [128]. The treatment of male rats with 8,000 ppm pyrethrins, female rats with 3,000 and 8,000 ppm pyrethrins, and both sexes with phenobarbital resulted in increased thyroid gland... 

Metabolites of PCBs also exert biological effects. The Ah-receptor mediated responses, however, are probably caused by the parent compounds only. The effects of hydroxylated PCBs include inhibition of cytochrome P450-dependent enzyme activities and competitive interference with thyroid hormone and vitamin A metabolism.89,90 Methylsulfonyl-PCBs have been shown to inhibit aryl hydrocarbon hydroxylase activity91 and to elicit phenobarbital-type toxicity and may in fact be responsible for the observed effect presumed to be caused by the parent compound.92... 

The properties of the ihicrosomal 26-hydroxylase seem to differ from those of the other microsomal side-chain hydroxylations. Treatment with phenobarbital had little or no influence on 26-hydroxylation of 5yS-cholestane-3a,7a,12a-triol but stimulated the other hydroxylations up to 8-fold [126]. Thyroid hormone stimulated the microsomal 26-hydroxylase, which might be of importance for the regulation of the ratio between cholic and chenodeoxycholic acid in the rat (cf. below). Biliary obstruction inhibited [127] whereas biliary drainage and starvation have little or no effect [126]. 

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