Thyroxine and Triiodothyronine Kinetics and Extrathyroidal Peripheral Conversion Rate of Thyroxine to Triiodothyronine in Healthy Elderly Humans

Jm, Miralles-García; García-Iglesias, C; F, De Pablo-Dávilà; Jm, Lanao; S, Castro del Pozo

doi:10.1055/s-2007-1019356

Cited by 9 publications

(5 citation statements)

References 13 publications

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“…In contrast to T 4 levels, serum free T 3 concentrations showed a significant decline with age in the present study, corresponding to the observations by Burrows et al (1975) and Rubenstein, Butler and Werner (1973). This observed fall in serum T 3 in old age has been suggested by Hansen, Skousted and Siersbaek-Nielsen (1975) to be caused by a decrease in T 3 production, whereas Mirales- Garcia et al (1981) suggested that an increased daily turnover of T 3 lowered serum T 3 .…”

Section: Discussioncontrasting

confidence: 60%

Nuclear Thyroxine and Triiodothyronine Binding in Mononuclear Cells in Dependence of Age

Kvetny¹

1985

Horm Metab Res

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Nuclear binding of thyroxine (T4) and triiodothyronine (T3) in mononuclear blood cells was investigated in 12 young (age 16-30 years) healthy subjects (group A), in 12 middle-aged (age 31-60 years) healthy subjects (group B) and in 12 elderly (61-90 years) healthy subjects. Serum free T3 was depressed in group C as compared to the younger age groups, whereas serum free T4 and TSH did not differ between the groups. Maximal specific nuclear binding capacity for both T4 and T3 decreased with increasing age, T4 group A: 1.2 fmol T4/100 micrograms DNA, group B: 1.2 fmol T4/100 micrograms DNA, group C: 0.7 fmol T4/100 micrograms DNA; T3 group A: 1.7 fmol T3/100 micrograms DNA, group B: 1.0 fmol T3/100 micrograms DNA, group C: 0.9 fmol T3/100 micrograms DNA. The equilibrium association constant (Ka) for T4 increased with age, group A: Ka = 3.3 X 10(9) l/mol, group B: Ka = 3.2 X 10(9) l/mol, group C: Ka = 6.4 X 10(9) l/mol, whereas Ka for nuclear binding of T3 decreased with age group A: Ka = 3.9 X 10(9) l/mol, group B: Ka = 5.9 X 10(9) l/mol, group C: Ka = 1.8 X 10(9) l/mol. We conclude that, whereas the opposite variations of nuclear capacity and binding affinity for T4 tend to preserve the nuclear T4 concentration, the nuclear T3 concentration definitely decreases with age. The unaltered serum levels of TSH suggest that the decrease of both serum levels of free T3 and the nuclear T3 concentration might represent physiologically changes in old age.

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Section: Discussioncontrasting

confidence: 60%

Nuclear Thyroxine and Triiodothyronine Binding in Mononuclear Cells in Dependence of Age

Kvetny¹

1985

Horm Metab Res

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“…T4 metabolism has been shown in some studies to be reduced in the elderly (17), though this may be related to the increased frequencies of nonthyroidal illnesses and medication intake in this age group. T4 to T3 conversion appears to be normal in healthy elderly individuals (18)(19)(20), though some reduction has been reported (21). While some have recommended reduction in T4 replacement dosage in the elderly (22), the present findings would suggest the opposite.…”

Section: Aging Effect On T4 Absorptioncontrasting

confidence: 69%

Human Thyroxine Absorption: Age Effects and Methodological Analyses

Hays¹,

Nielsen²

1994

Thyroid

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Experience with the use of simultaneous oral and iv radioiodine tracers of thyroxine (T4) to measure T4 absorption was reviewed to determine the effect of advanced age on T4 absorption and to search for acceptable simplifications in the measurement methodology. (1) Age effect: In control subjects, T4 absorption did not differ with age between 21 and 69 years; it averaged 62.8 +/- 13.5% (SD) in subjects over age 70 compared with 69.3 +/- 11.9% in subjects aged 21-69 (p < 0.001). We conclude that, because of this small but significant reduction in T4 absorption efficiency in the elderly, it is especially important to monitor individual response to replacement T4 doses in this age group. (2) Methodology studies: Intrasubject coefficient of variation for T4 absorption in triplicate studies averaged 8.9%, when an identical method was used at weekly intervals (n = 3). When the 3 studies were done by 3 separate methods (sequential po and i.v. 123I-labeled T4, sequential 125I-labeled T4 po and i.v., and simultaneous po and i.v. doses of different tracers), the intrasubject coefficient of variation averaged 9.8% (n = 8). When the absorption calculation used only one serum sample, taken after isotopic equilibrium was achieved at 24 h [the double isotope (eq) method], calculated T4 absorption differed little from that calculated in the same subjects using a full serum time-activity curve and a noncompartmental analysis [the double isotope (AUC) method]. Compared with a compartmental model solution, both methods slightly overestimated T4 absorption. In 4 subjects given i.v. radioiodide as a third tracer at the same time demonstrated that, as long as radioiodide contamination of the T4 tracers is measured and accounted for in the standards, contaminating radioiodide has no clinically significant effect on T4 absorption measurements. When an oral tracer of T4 was considered alone, without an i.v. tracer to correct for T4 metabolism, the estimates of T4 absorption correlated in a curvilinear fashion with T4 absorption as measured by the double isotope method. Except at very low absorption levels, the oral tracer alone is a poor predictor of T4 absorption. We conclude that, when using a double isotope method to measure T4 absorption, it is acceptable to rely on a single serum sample taken at 24 h, a time when isotopic equilibrium between the two tracers has been reached.(ABSTRACT TRUNCATED AT 400 WORDS)

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“…Of these, five were above the age of 65 years (elderly group), the remainder were between the ages of 18 and 26 years (young group). Each subject received through an antecubital vein approximately 50 juCi of 125 I-T 3 (Amersham Radiochemical Center, England), which specific activity was 200-400 uCi/4.3-13.6 ug, following a previously described protocol (Miralles-Garcia, Garcia-Iglesias, De Pablo, Lanao and Castro 1981). Simultaneously, also by intravenous vein, 100 uCi of sterile 51 Cr-EDTA (Amersham Radiochemical Center, England) (specific activity 1-2 mCi/mg) was administered, for the simultaneous study of renal glomerular filtration, according to the bicompartmental model (Brien, O 'Hagan and Muldowney 1969).…”

Section: Methodsmentioning

confidence: 99%

“…In a previous work {Miralles- Garcia, Garcia-Iglesias, De Pablo, Lanao and Castro 1981), we have investigated the influence of age on the kinetics of both thyroid hormones, and the level of peripheral conversion of T 4 to T 3 in the elderly. We found no significant difference in the behavior of T 4 in these subjects.…”

Section: Introductionmentioning

confidence: 99%

Urinary Kinetics of Triiodothyronine and their Modification with Aging

Jm¹,

Mt²,

Reglero-Chillón³

et al. 1985

Horm Metab Res

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The urinary kinetics of triiodothyronine (T3) in healthy young and old people has been studied. The behavior of urinary excretion is similar in both age groups, expressed in our mathematical model in the cumulative kinetics as well as in the urinary rate. However, a significant decrease (P < 0.025) of renal clearance of T3 in elderly individuals has been found. No significant differences (P > 0.05) were observed in any other kinetic parameters. The possible influence of the reduction of glomerular filtrate has been discussed as the most important pathogenic factor of the decreased renal clearance of this hormone. Possibly, modifications of the distribution volumes are also involved. Due to the limited number of persons studied, for ethical reasons, the results obtained are not definitive.

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Thyroxine and Triiodothyronine Kinetics and Extrathyroidal Peripheral Conversion Rate of Thyroxine to Triiodothyronine in Healthy Elderly Humans

Cited by 9 publications

References 13 publications

Nuclear Thyroxine and Triiodothyronine Binding in Mononuclear Cells in Dependence of Age

Nuclear Thyroxine and Triiodothyronine Binding in Mononuclear Cells in Dependence of Age

Human Thyroxine Absorption: Age Effects and Methodological Analyses

Urinary Kinetics of Triiodothyronine and their Modification with Aging

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