Aging thyroid hormones

The metabolic rate is increased by several hormones including thyi oid hormone, adrenalin and male sex hormones. The increase in metabolic rate caused by male sex hormones explains why males have slightly higher average metabolic rates than females of the same size and age. Living in a cold climate increases the metabolic rate because the cold stimulates thyroid hormone production and this hormone increases heat output of the body, while living in a warm climate causes the metabolic rate to decrease. 

Hormonal actions occur during sensitive periods in development, in adult life during natural endocrine cycles and in response to experience as well as during the aging process (see Ch. 30). As a result of their fundamental actions on cellular processes and genomic activity and of the control of their secretion by environmental signals, steroid and thyroid hormone actions on the brain provide unique insights into the plasticity of the brain and behavior (see also Ch. 50). 

Ah-responsive and Ah-nonresponsive strains females, age 10 weeks given single ip injection of 50 mg/kg BW killed after 7 days Both groups had increased body weight, increased blood EROD activity, decreased plasma retinol levels, and increased plasma total thyroid hormone levels. The Ah-responsive group also had increased hepatic pentoxyresorufin-O-deethylase activity, increased livercytochrome P-450 activity, and increased liver weight 12... 

The therapeutic objectives for hyperthyroidism are to normalize the production of thyroid hormone minimize symptoms and long-term consequences and provide individualized therapy based on the type and severity of disease, patient age and gender, existence of nonthyroidal conditions, and response to previous therapy. 

Hyperthyroidism is a fairly common complaint which may occur at any age, but affects mainly females. There are several causes of increased thyroid hormone secretion but only rarely is the condition due to non-thyroidal (e.g. pituitary) illness. 

Children s Susceptibility. Neurodevelopmental delays and postnatal changes in serum thyroid hormone levels have been observed in animals following exposure of their mothers to chlorine dioxide or chlorite during gestation and/or lactation (Carlton and Smith 1985 Carlton et al. 1987 Gill et al. 2000 Mobley et al. 1990 Orme et al. 1985 Taylor and Pfohl 1985 Toth et al. 1990). It is not known whether age-related differences in toxicokinetic parameters exist for chlorine dioxide or chlorite. Additional studies should be designed to further examine neurodevelopmental toxicity and underlying mechanisms. 

Thyroid hormone also plays a major role in the maturation of bone. A deficiency of thyroid hormone in early life leads to both delay in and abnormal development of epiphyseal centers of ossification (epiphyseal dysgenesis). Hypothyroidism-induced impairment of linear growth can lead to dwarfism in which the Umbs are disproportionately short in relation to the trunk with the apparent bone age retarded in relation to chronological age. 

Subclinical hypothyroidism, defined as an elevated TSH level and normal thyroid hormone levels, is found in 4-10% of the general population but increases to 20% in women older than age 50. The consensus of expert thyroid organizations concluded that thyroid hormone therapy should be considered for patients with TSH levels greater than 10 mlU/L while close TSH monitoring is appropriate for those with lower TSH elevations. 

Ballard PL, Ballard RA, Ning Y, Cnann A, Boardman C, Pinto-Martin J, Polk D, Phibbs RH, Davis DJ, Mannino FL, Hart M. Plasma thyroid hormones in premature infants effect of gestational age and antenatal thyrotropin-releasing hormone treatment. TRH Collaborative Trial Participants. Pediatr Res 1998 44(5) 642-9. 

In a retrospective review of 497 patients taking propylthiouracil for hyperthyroidism, clinically overt hepatitis developed in six patients at 12-49 days after starting the drug (50). Jaundice and itching were present in five, fever in two, rash in two, and arthralgia in one. Serum bilirubin, alanine transaminase, and alkaline phosphatase were increased in five, four, and six patients respectively. The type of hepatic injury was cholestatic in three, hepatocellular in one, and mixed in two. There were no differences in age, sex, drug dose, or serum thyroid hormone concentrations at time of diagnosis in those with hepatic injury compared with those without. Liver function normalized in all patients at 16-145 days after withdrawal of propylthiouracil. In addition to these cases of overt liver injury, 14% of the cohort had mild asymptomatic liver enzyme rises at a mean of 75 days after the start of treatment. 

Thyroid hormones are among the most commonly prescribed drugs in the developed world, with a prevalence of prescription of 5-10% in the over 60 age group (3,4). Since about 25% of those who use thyroxine (T4) take doses sufficient to suppress serum TSH (4,5), much attention has focussed on potential adverse effects of this degree of over-treatment. 

Herlihy JT, Stacy C, Bertrand HA. Long-term food restriction depresses serum thyroid hormone concentrations in the rat. Mech Ageing Dev 1990 53 9-16. 

Osteoporosis occurs when bone mass is less than one would expect for the average person of a specific age. Osteoporosis can have many causes. The reduction of the female hormone estrogen after menopause is the most common. Persons who have increased thyroid hormone (hyperthyroid) can become osteoporotic. Patients receiving steroids for long periods of time, either as medication or because of adrenal disease (Cushing s disease) are also at risk. 

Those living in this region have been found to exhibit decreased gestational age, low birth weights, developmental effects in children, neurological defects in newborns, increased infertility, changes in sex ratios of children born, and thyroid hormone fluctuations. I54 ... 

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