Comparison between the thyrotropin response to thyrotropin-releasing hormone in summer and that in winter in normal subjects.

Konno, N

doi:10.1507/endocrj1954.25.635

Cited by 20 publications

(4 citation statements)

References 13 publications

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“…This discrepancy in TSH regulation between the previous reports and our study may be because the adequacy of therapy was established by normal TSH response to TRH administration in this study rather than normalization of basal TSH alone. This finding is consistent with previous reports of lack of seasonal variation in TSH response to TRH administration in normal subjects (Konno, 1978;Konno, 1980).…”

Section: Discussionsupporting

confidence: 93%

Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism

Kabadi

1985

Postgraduate Medical Journal

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Summary:Normalization of basal thyrotrophin (TSH) level is used as the endpoint in L-thyroxine (L-T4) therapy ofprimary hypothyroidism. However, several reports have questioned the reliability of this index because of seasonal variation of TSH. Therefore, we studied 85 consecutive patients with primary hypothyroidism over a period of 3.5 y. In these patients, TSH response (ATSH) to intravenous thyrotrophin releasing hormone (TRH) administration was examined when basal TSH was normalized with L-T4 therapy. Eight patients showed a blunted response (ATSH< 51LU), whereas 27 patients demonstrated an exaggerated response (ATSH > 25 JsU). Thus, 42% of patients were apparently on inappropriate L-T4 dosage. These abnormal TSH responses normalized on adjusting the L-T4 dosage alone; prolonged therapy with the same dose failed to normalize TSH responses. Minor seasonal variations of basal TSH were observed in 30% of patients. However, TSH response to TRH remained normal. Hence, no adjustment of L-thyroxine dose was required. This study, therefore, demonstrates that normalization of TSH response to TRH administration rather than basal TSH may be the best index of adequate L-thyroxine therapy in primary hypothyroidism.

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Section: Discussionsupporting

confidence: 93%

Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism

Kabadi

1985

Postgraduate Medical Journal

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“…This favors a genetic component in determining the pattern of TSH secretion. Table 4 lists some longitudinal studies of seasonal variation in thyroid function tests in healthy adults (14,29,30,(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65)(66)(67). In general, serum T 3 was higher during winter while seasonal changes in T 4 and TSH were less consistent.…”

Section: Circadian Variationmentioning

confidence: 99%

Biologic Variation is Important for Interpretation of Thyroid Function Tests

Andersen

Bruun²,

Pedersen³

et al. 2003

Thyroid

212

142

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Large variations exist in thyrotropin (TSH) and thyroid hormones in serum. The components of variation include preanalytical, analytical, and biologic variation. This is divided into between- and within-individual variation. The latter consists of circadian and seasonal differences although there are indicators of a genetically determined starting point. The ratio of within- to between-individual variation describes the reliability of population-based reference ranges. This ratio is low for serum TSH, thyroxine (T(4)) and triiodothyronine (T(3)) indicating that laboratory reference ranges are relatively insensitive to aberrations from normality in the individual. Solutions are considered but reducing the analytical variation below the calculated analytical goals of 7%, 5% and 12% for serum T(3), T(4), and TSH does not improve diagnostic performance. Neither does determination of the individual set-point and reference range. In practice this means that population-based reference ranges are necessary but that it is important to recognize their limitations for use in individuals. Serum TSH responds with amplification to minor alterations in T(4) and T(3). A consistently abnormal TSH probably indicates that T(4) and T(3) are not normal for the individual even when inside the laboratory reference range. This underlines the importance of TSH in diagnosis and monitoring of thyroid dysfunctions. Also, it implies that subclinical thyroid disease may be defined in purely biochemical terms. Under critical circumstances such as pregnancy where normal thyroid function is of importance for fetal brain development, subclinical thyroid disease should be treated. Even TSH within the reference range may be associated with slightly abnormal thyroid function of the individual. The clinical importance of such small abnormalities in thyroid function in small children and pregnant women for brain development remains to be elucidated.

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“…Other studies have, however, led to opposite results. In healthy subjects serum total T 4 levels were similar during all seasons, but the serum thyrotrophin (TSH) response to TSH-releasing hormone (TRH) was greater in winter than in summer (Konno 1978, Harrop et al 1985. In hypothyroid subjects, lower serum T 4 levels and higher serum TSH levels and TSH responses to TRH were found in winter rather than in summer (Konno & Morikawa 1982).…”

Section: Introductionmentioning

confidence: 98%

The pituitary-thyroid axis in healthy men living under subarctic climatological conditions

Hassi

Sikkilä²,

Ruokonen³

et al. 2001

Journal of Endocrinology

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In order to evaluate the effects of climatic factors on the secretion of thyroid hormones and TSH in a high latitude population, we have taken serum and urine samples from 20 healthy men from northern Finland (67 -68 N) every 2 months for a period of 14 months. Serum free triiodothyronine (T 3 ) levels were lower in February than in August (3·9 vs 4·4 pmol/l, P<0·05) and TSH levels were higher in December than during other months (2·1 vs 1·5-1·7 mU/l, P<0·01). Serum total and free thyroxine (T 4 ), total T 3 and reverse T 3 levels and urinary T 4 levels were unchanged. Urinary T 3 levels were significantly higher in winter than in summer. Serum free T 3 correlated highly significantly with the outdoor temperature integrated backwards weekly for 7-56 days (r=0·26 for 1-56 days) from the day when the blood samples were taken. Serum TSH did not show any significant correlation with the thyroid hormones or with the integrated temperature of the previous days, but it did show an inverse and significant correlation (r= 0·31) with the ambient luminosity integrated backwards for 7 days from the day when the blood sample was taken. The gradually increasing correlation between outdoor temperatures and serum free T 3 suggests that the disposal of thyroid hormones is accelerated in winter, leading to low serum free T 3 levels and a high urinary free T 3 excretion. Since there was no correlation between thyroid hormones and serum TSH, the feedback mechanism between TSH and thyroid hormones may not be the only contributing factor, and other factors such as ambient luminosity may at least partly determine serum TSH in these conditions. Also urinary free T 3 appears to be a novel and non-invasive indicator for thyroid physiology.

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Comparison between the thyrotropin response to thyrotropin-releasing hormone in summer and that in winter in normal subjects.

Cited by 20 publications

References 13 publications

Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism

Normal thyrotrophin response to intravenous thyrotrophin releasing hormone administration: the best index of optimal L-thyroxine therapy in primary hypothyroidism

Biologic Variation is Important for Interpretation of Thyroid Function Tests

The pituitary-thyroid axis in healthy men living under subarctic climatological conditions

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