Thyroxine serum

B45. Brent, G. A., and Hershman, J. M Thyroxine therapy in patients with severe nonthyroidal illness and low serum thyroxine concentration. J. Clin. Endocrinol. Metab. 63, 1-8 (1986). 

Oral gavage of rat pups with 14mg/kg/day ftom posmatal day 5 through 20 caused reductions in serum thyroxine levels that correlated with depressed behavioral parameters. Further studies using the same protocol reported decreased cell proliferation in the cerebellum and forebrain on postnatal days 11 and 21, respectively. In yet another study, 14mg/day of chlorine dioxide on posmatal days 1-20 was associated with some neurotoxicity (decreased forebrain weight and reduced synapse formation on day 35), but the neurotoxicity was not correlated with any antithyroid activity of this chemical. ... 

Oral contraceptives have also been reported to produce increases in sulfobromophthalein retention and other liver function tests, as well as in prothrombin time, clotting factors VII, VIII, IX, serum thyroxine, and protein-bound iodine (B8). In a group of 48 women the mean cholesterol value was 206 41 mg/100 ml while they were receiving a variety of oral contraceptives and 179 28 mg/100 ml when they were not receiving the drugs (W19). 

Lab test abnormalities Phenytoin may decrease serum thyroxine and free thyroxine concentrations. 

In a six-month inhalation study, New Zealand White rabbits and Sprague-Dawley rats were exposed by inhalation to 0, 98 or 745 ppm [0, 245 or 1860 mg/m ] nitromethane for 7 h per day on five days per week for six months. Decreased body weight gain in rats was seen after eight weeks of exposure to 745 ppm. The most notable response in rabbits was an effect on the thyroid increased thyroid weight and decreased serum thyroxine levels. There were no exposure-related gross or microscopic lesions in either rats or rabbits exposed to 98 or 745 ppm (Lewis et al, 1979). 

During the acute phase of thyrotoxicosis, B-adrenoceptor blocking agents without intrinsic sympathomimetic activity are extremely helpful. Propranolol, 20-40 mg orally every 6 hours, will control tachycardia, hypertension, and atrial fibrillation. Propranolol is gradually withdrawn as serum thyroxine levels return to normal. Diltiazem, 90-120 mg three or four times daily, can be used to control tachycardia in patients in whom blockers are contraindicated, eg, those with asthma. Other calcium channel blockers may not be as effective as diltiazem. Adequate nutrition and vitamin supplements are essential. Barbiturates accelerate T4 breakdown (by hepatic enzyme induction) and may be helpful both as sedatives and to lower T4... 

A potential biomarker of exposure to PBDEs relates to their effect on the thyroid gland. As discussed in Sections 3.2.2.2, Endocrine Effects, thyroid changes in rats and mice include reduced serum thyroxine (T4) levels w itli no changes in scrum TSH (Damerud and Sinjari 1996 Fowles et al. 1994 Hallgren and Damemd 1998 WIL Research Laboratories 1984 Zhou et al. 2001, 2002). Additional studies are needed to characterize thyroid effects of PBDEs in humans and develop specific correlations between levels and duration of exposure and alterations in senun levels of T4. This potential biomarker is not specific to PBDEs because PBBs and other antithyroid agents can have similar effects. 

Systemic iodine absorption can occur after intravaginal administration of povidone-iodine (11). There were increases in serum iodine, protein-bound iodine, and inorganic iodine, but not serum thyroxine, after a 2-minute vaginal administration of povidone-iodine in non-preg-nant women (12). 

Thyroid function tests are often altered by somatropin because of increased conversion of T4 to T3, but this is clinically insignificant at low doses (SEDA-21, 453). One child with Prader-Willi syndrome had a fall in serum thyroxine concentration during somatropin therapy and needed thyroxine replacement (33). Hypothyroidism developed in 11 of 46 growth hormone-deficient children treated with somatropin (34). Prior abnormalities in hypothalamic-pituitary function and alterations in thyroid hormone metabolism, probably both, contributed to the high incidence of hypothyroidism, which was similar to that in previous studies. 

A 72-year-old woman with dilated cardiomyopathy was given amiodarone for fast atrial flutter and 6 months later developed abnormal thyroid function tests, with a suppressed TSH and a raised serum thyroxine. The autoantibody profile was negative and a thyroid uptake scan showed reduced uptake (44). 

Despite the fact that she was clinically euthyroid, the authors suggested that this patient had amiodarone-induced hyperthyroidism. However, amiodarone inhibits the peripheral conversion of thyroxine to triiodothyronine it can therefore increase the serum thyroxine and suppress the serum TSH, as in this case. On the other hand, the reduced uptake by the thyroid gland is consistent with type 2 amiodarone-induced hyperthyroidism. The authors did not report the serum concentrations of free thyroxine and triiodothyronine. 

Gl. Galen, R. S., and Forman, D., Enzyme immunoassay of serum thyroxine with the AutoChemist multichannel analyzer. Clin. Chem. 23, 119—121 (1977). 

At 100 ppm, reductions in serum thyroxine and hypothalmic norepinephrine concentrations, increases in adrenal catecholamines and serum cortocosterone, no effect on body organ weight except for a slight decrease in liver weight. 

Radioimmunoassay. In serum thyroxine and liothyronine, detection limit 10 ng/ml and 260pg/ml, respectively—C. E. Denning et al., Clinica chim. Acta, 1979, 98, 5-18. 

Endogenous serum-thyroxine concentrations range from 0.05 to... 

S) 9.9-98 (SE) antiestrogenic, antiestrogenic TOEI strong in rodents MC-type decrease of plasma testosterone in male rats and of serum thyroxine. Porphyrogenic in mice and rats. TOEI strong MC-type adult human (fat) range fish medeka (10% lipid) 390 104-670 510,000 430 115-740 5,100,000... 

Rats and pigs showed dose related decreases in serum thyroxine and triiodothyronine. There was also a pronounced influence of PBBs on vitamin A storage above a no observed effect level of 0.1 mg/kg body weight/day [2]. This effect does probably also involve hydroxy-metabolites, since this is also the case with PCBs. 

Total serum thyroxine levels as measured by the total protein bound levels after injury have been reported as raised (F4), unchanged, or lowered (SI) but it is now agreed that there is no significant increase in total hormone levels in blood in the postoperative period. 

Based on this principle, practical assays for human serum thyroxine and theophylline have been developed and different distinct classes of modulators have been investigated. 

Finley, P.R. WiUiams, R.J. Lichti, D.A. Evaluation of a new homogeneous enzyme-inhibitor immunoassay of serum thyroxine with use of a bichromatic analyzer. Clin. Chem. 1980, 26, 1723-1726. 

Chronic dosing in pregnant rats has resulted in increased rates of cleft palate formation as well as decrease in serum thyroxine levels. Prenatal exposure to benzodiazepines in rats describes learning and memory deficits in pups as well as absence of usual startle responses. 

The serum thyroid-stimulating hormone (TSH) is at a maximum between 0200 and 0400 and at a minimum between 1800 and 2200. The variation is of the order of 50%. There are also variations in the serum thyroxine concentration, but these appear to be related to the changes in concentration of binding protein brought about by changes in posture. These variations are maximal between 1000 and 1400. Total protein concentration may vary by as much as 10% over 24 hours, but the variation of individual proteins may be even greater. 

Phenytoin decreases the urinary excretion of 17-ketosteroids and 17-hydroxycorticosteroids by stimulating the conversion of cortisol to 6-P-hydroxycortisol it also diminishes serum FSH and the sperm count in semen, and thereby reduces fertility, Phenytoin also lowers the serum thyroxine concentration, probably by competitive displacement of thyroxine from its protein-binding sites free thyroxine also tends to be low. Serum triiodothyronine is low, probably as a result of stimulated metabohsm in the liver, but the concentration of TSH is unaffected by the altered thyroxine metabolism. 

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