Cytochrome thyroid hormone effect

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... 

Lawrle, R. A. (1953) The activity of the cytochrome system In muscle and Its relation to myoglobin. Blochem. J. 55 298-305. Lawrle, R. A. (1953) Effect of enforced exercise on myoglobin concentration In muscle. Nature London. 171 1069-71. John-Alder, H. (1984) Seasonal variations In activity, aerobic energetic capacities, and plasma thyroid hormones (T3 and T4)... 

Liu, D. and D.J. Waxman (2002). Post-transcriptional regulation of hepatic NADPH-cytochrome P450 reductase by thyroid hormone Independent effects on poly(A) tail length and mRNA stability. Mol. Pharmacol. 61, 1089-1096. 

It has also been hypothesized that long-term hormone imbalance can induce cancers in endocrine-sensitive organs, such as gonads, adrenals, thyroid, prostate, and breast. Lipid-soluble compounds are of special concern because they are retained in the body, therefore causing a long-term effect. Some of these chemicals are known cytochrome P450 enzyme inducers, such as PCBs, DDT, and butylated hydro-xytoluene, and have been implicated in cancers in the adrenals, uterus, and thyroid. 

Chronic renal disease may also affect metabolism, not necessarily because of impaired metabolism in the kidney, but because of an indirect effect of renal failure on liver metabolism. For example, in animals with renal failure it was observed that there was a decrease in hepatic cytochromes P-450 content, and consequently zoxazolamine paralysis time and ketamine narcosis time were prolonged. Cardiac failure may also affect metabolism by altering hepatic blood flow. However even after heart attack without hypotension or cardiac failure, metabolism may be affected. For example, the plasma clearance of lidocaine is reduced in this situation. Other diseases such as those which affect hormone levels hyper- or hypo-thyroidism, lack of or excess growth hormone, and diabetes can alter the metabolism of foreign compounds. 

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