Age-Related Changes of Serum 3,3′-Diiodothyronine, 3′,5′-Diiodothyronine, and 3,5-Diiodothyronine Concentrations in Man

Abstract

To evaluate the effects of aging on T4 metabolism, serum 3,3'diiodothyronine (3,3'-T2), 3',5'-diiodothyronine (3',5'-T2), and 3,5-diiodothyronine (3,5-T2) as well as T4, T3, and rT3 concentrations were determined by RIAs in 81 normal subjects, aged 24-81 yr. 3,3'-T2, 3',5'-T2, and 3,5-T2 antisera were prepared by immunizing rabbits with the protein conjugate of each diiodothyronine. Since the 3',5'-T2 antiserum cross-reacted with rT3 to the extent of 1.8%, correction was made by subtracting 1.8% of the rT3 value from the measured 3',5'-T2 value. The other 2 antisera had no noticeable cross-reactivity with various thyroid hormone derivatives. Although no significant relation existed between T4 levels and age (r = -0.14; P greater than 0.1) serum T3 showed a significant correlation with age (r = -0.28; P less than 0.05). In contrast, no significant correlation was observed between rT3 and age (r = 0.12; P greater than 0.1). Serum 3,3'-T2, 3',5'-Tw, and 3,5-T2 values (nanograms per dl) all had significant inverse correlations with age, the coefficients of correlation being -0.38 for 3,3'-T2 (P less than 0.01), -0.58 for 3',5'-Tw (P less than 0.01), and -0.47 for 3,5-T2 (P less than 0.01). These findings suggest that sequential monodeiodinating activities in T4 metabolism decrease with increasing age.

Translating Pharmacological Findings from Hypothyroid Rodents to Euthyroid Humans: Is There a Functional Role of Endogenous 3,5-T2?

“…One possible explanation might be the brief incubation time of almost one hour in most polyclonal antibody-based RIAs compared with the overnight incubation performed in our monoclonal antibody immunoassay. Furthermore, previously reported age- (16) or sex-related (15) differences in serum 3,5-T2 concentrations were not confirmed by the present analyses. The small sample sizes of the former studies including 81 (16) or 52 (15) subjects might be the most likely reason.…”

“…Compared with results reported in previous studies on euthyroid humans, we measured markedly higher median serum 3,5-T2 concentration (15)(16)(17)(18)(19)(29)(30)(31)(32)(33). One possible explanation might be the brief incubation time of almost one hour in most polyclonal antibody-based RIAs compared with the overnight incubation performed in our monoclonal antibody immunoassay.…”

“…Following the development of 3,5-T2 radioimmunoassays (RIAs), age-and sex-specific differences in serum 3,5-T2 concentrations (15,16) as well as associations with chronic renal diseases, liver cirrhosis, and sepsis were reported (17)(18)(19). Nevertheless, a validation of many of those associations in larger studies is lacking.…”

Estudo da Função Tiroideana em Uma População com Mais de 50 Anos

“…Um estudo com idosos internados demonstrou que os níveis de FT4 diminuem com a idade, mas aumentam proporcionalmente com a gravidade da doença (41). Com relação aos níveis séricos de T3, vários estudos demonstraram uma diminuição progressiva com a idade (9,18,19,23,25,26), chegando a 5,1ng/dl por década (25), embora o T3 reverso não tenha mostrado a mesma tendência (23,26). Por outro lado, outros trabalhos não confirmaram esta tendência na queda do T3 em função da idade (14,24,27).…”

“…Alguns autores concordam que, com a idade, ocorra uma diminuição dos níveis séricos de T3, T4 e FT4 (9,14,(18)(19)(20)(21)(22)(23)25,26), enquanto para outros estes se mantém inalterados (14,23,24,27) com o envelhecimento. Níveis elevados (4,8,14) de TSH, baixos (15)(16)(17) ou inalterados (18) já foram descritos na população idosa.…”