Thyroid hormones long-term effects

Adverse reproductive effects have been observed in animals fed PCB in the diet. Fetal resorptions were common, and dose-related incidences of terata were found in pups and piglets when females were fed Arochlor 1254 at Img/kg/day or more. Long-term low-level maternal exposure of rats before breeding and throughout gestation and lactation caused permanent hearing deficits, decreased serum thyroid hormones, and reproductive effects. PCBs have been observed in human cord blood and in tissues of newborn humans and animals. ... 

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. 

Uses Thyroid hormones (levothyroxine, T4, and liothyronine, T3) are used to treat overt hypothyroidism. In addition, supra-physiological doses of levothyroxine are widely used to reduce the risk of thyroid cancer recurrence by suppressing serum TSH concentrations. The use of levothyroxine suppressive therapy to induce shrinkage of benign thjnoid nodules remains controversial and its routine use is not recommended in view of its low efficacy and potential long-term effects on the cardiovascular system and the skeleton caused by the induction of subchnical hjrper-thyroidism [5 ]. 

Endocrine Based on the analysis of biomarkers in urine, a positive association between triclosan and total triiodo-thyonine (T3) concentrations in adolescents was observed. Based on these findings, the authors suggested that triclosan exposure may potentially be associated with altered thyroid hormone levels [bl ]. Another study (which was funded by a toothpaste manufacturer) on the long-term effects of triclosan-containing toothpaste on thyroid function was unable to find a detectable effect [62 j. 

Uzzan B, Campos J, Cucherat M, Nony P, Boissel JP, Perret GY. Effects on bone mass of long term treatment with thyroid hormones a meta-analysis. J Clin Endocrinol Metab 1996 81(12) 4278-89. 

The primary method of treating hypothyroidism is to administer thyroid hormones as replacement therapy. Long-term administration of thyroid hormones is usually a safe, effective means of maintaining optimal patient health in hypothyroidism. Replacement therapy using thyroid hormone preparations is described below. 

Sin YM, Teh WF. 1992. Effect of long-term uptake of mercuric sulphide on thyroid hormones and glutathione in mice. Bull Environ Contain Toxicol 49(6) 847-854. 

Effects on the Pituitary. Somatostatin inhibits GH and thyrotropin releasing hormone (TRH)-induced thyroid stimulating hormone (TSH) release from the pituitary. No effects on other pituitary hormones were observed in normal subjects. The inhibition of GH release by somatostatin suggests a use in the treatment of acromegaly. The value of GH release inhibition as long-term therpay cannot be predicted. 

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