Plasma Thyrotropin and Its Response to Thyrotropin Releasing Hormone in Normal Pregnancy

Kannan, K.; Mk, Sinha; Pk, Devi; Gk, Rastogi

doi:10.1097/00006250-197310000-00011

Cited by 26 publications

(12 citation statements)

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“…We have already mentioned some arguments suggesting that elevated estrogen levels in pregnancy may influence the HPTA, perhaps by acting directly at different (and not yet clearly defined) levels in the thyroid gland feedback-regulatory mechanisms. In his 1993 review in Endocrine Reviews, Burrow (48) analyzed in detail the few available studies in which the HPTA has been assessed, either by the administration of T 4 or T 3 to pregnant women for short periods with the aim of evaluating the TSH responses to induced hormonal changes (75,76,90,91) or after TRH administration (52,(92)(93)(94). Unfortunately these studies, performed before 1980, employed the then available assays which were unable to detect subtle serum TSH changes.…”

Section: E the Hypothalamic-pituitary Control Of Thyroid Function Anmentioning

confidence: 99%

“…In earlier work, conflicting data have been reported: some authors found no change in serum TSH in pregnancy (95,96), while others observed significant increases in TSH throughout gestation (93,97). With the introduction 10 yr ago of sensitive immunoradiometric techniques allowing for extremely precise determinations of TSH levels within the normal range, new and important insights have been gained to better define the patterns of serum TSH changes during pregnancy.…”

Section: Regulation Of Serum Tshmentioning

confidence: 99%

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The Regulation of Thyroid Function in Pregnancy: Pathways of Endocrine Adaptation from Physiology to Pathology

1997

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Section: E the Hypothalamic-pituitary Control Of Thyroid Function Anmentioning

confidence: 99%

Section: Regulation Of Serum Tshmentioning

confidence: 99%

The Regulation of Thyroid Function in Pregnancy: Pathways of Endocrine Adaptation from Physiology to Pathology

1997

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“…In fact, the TSH response to TRH during pregnancy has been studied, and no difference from the response in nonpregnant subjects was found (12,13). However, there has been no previous effort to study the response to TRH specifically in those patients who have demonstrably elevated free T 4 concentrations.…”

mentioning

confidence: 99%

Components of the Total Serum Thyroid Hormone Concentrations during Pregnancy: HighFree Thyroxine and Blunted Thyrotropin (TSH) Response to TSHReleasing Hormone in the First Trimester*

Guillaume

Schussler

Goldman

et al. 1985

The Journal of Clinical Endocrinology & Metabolism

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The distribution of thyroid hormones between free solution and their several protein-binding sites during pregnancy was studied under physiological conditions of temperature and pH. Single serum specimens were obtained from individual women at different stages of pregnancy. During the first 5 weeks of pregnancy, mean serum free T4 and free T3 concentrations were 50% higher than in nonpregnant women or women during the third trimester. Free T4 was increased significantly throughout the first trimester, but because of wide variance, free T3 was significantly above control values only during the first 5 weeks. Free T4 and free T3 concentrations decreased to control levels in the third trimester. These changes in free T4 concentrations are consistent with a weak thyrotropic action of hCG, which attained maximal concentrations early in the first trimester and then decreased markedly in the second and third trimesters. TRH testing of women scheduled for abortion in the first and second trimesters revealed marked inhibition of TSH response to TRH in those first trimester women who had elevated free T4 concentrations. The percent free T4 did not decrease during the first 5 weeks, but then declined progressively to term as T4-binding globulin (TBG) affinity, defined as the product of the capacity and affinity constant, progressively increased. T4 bound to TBG (T4-TBG) increased from early in the first trimester to term, and then decreased in postterm pregnancy and postpartum. T4 bound to prealbumin (T4-PA) and to albumin (T4-Alb) decreased significantly in the third trimester compared with either control or first trimester concentrations. The concentration of free T3 was positively correlated with T4-PA (r = 0.25) and T4-Alb (r = 0.31), but not with free T4 (r = 0.18) or T4-TBG (r = -0.30) concentrations. These results suggest that 1) only the high concentrations of hCG present in the first trimester of pregnancy have a thyrotropic effect in excess of normal levels of TSH, and this can be sufficient to suppress the TSH response to TRH; 2) hepatic TBG secretion continues to respond to the continuously rising estrogen levels throughout pregnancy; and 3) T4-PA and T4-Alb, but not free T4 or T4-TBG, are possible precursors for the extrathyroidal generation of T3.

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“…These discrepancies may be due to the use of TSH radioimmunoassays which were not sufficiently specific. Indeed, in the system used by Kannan et al (1973), the tracer was displaced by HCG at doses over 10 IU/tube. Comparable amounts of HCG are regularly observed in 0.1 ml of blood at various stages of pregnancy.…”

Section: Tsh Responsivenessmentioning

confidence: 99%

“…We have performed meas¬ urements of blood HCG in our patients, using a specific ß HCG homologous system described elsewhere (Vandalem et al 1975a) and we could not find any correlation between TSH and HCG blood levels. Kannan et al (1973) studied pituitary responsiveness to TRH in pregnancy and post-partum. During pregnancy, increase in TSH blood levels was similar in intensity to that of a control group, but was more prolonged.…”

Section: Tsh Responsivenessmentioning

confidence: 99%

Thyroliberin and Gonadoliberin Tests During Pregnancy and the Puerperium

Vandalem

Pirens

Hennen

et al. 1977

Acta Endocrinologica

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Highly specific and sensitive radioimmunoassays for HTSH, HFSH and HLH have been used in order to investigate pituitary thyrotrophic and gonadotrophic functions of pregnant and puerperal women. The radioimmunoassay system for HFSH, using reagents prepared in our laboratory, is described.Thirty-three women were studied during pregnancy and post-partum. Forty-one TRH tests were performed. Basal levels of TSH, and increase in serum TSH after intravenous injection of TRH were similar in pregnant and puerperal women and in a control group. Thirty-three LH-RH tests were also performed. Basal levels of LH and FSH remained undetectable throughout pregnancy and in early puerperium. Furthermore, after intravenous injection of LH-RH neither LH nor FSH activity could be detected.It has thus been demonstrated that pituitary responsiveness to TRH during pregnancy and the puerperium is similar to that of non-pregnant young women. In contrast, a complete cessation of pituitary gonadotrophic functions is observed during the same period.Due to an important degree of structural homology, antigenic relationships exist between human pituitary and chorionic glycoprotein hormones (human thyrotrophin: HTSH, human follitrophin: HFSH, human lutrophin: HLH and human chorionic gonadotrophin: HCG). This explains many of the difficulties Laboratoire d'Endocrinologie,

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Plasma Thyrotropin and Its Response to Thyrotropin Releasing Hormone in Normal Pregnancy

Cited by 26 publications

References 0 publications

The Regulation of Thyroid Function in Pregnancy: Pathways of Endocrine Adaptation from Physiology to Pathology

The Regulation of Thyroid Function in Pregnancy: Pathways of Endocrine Adaptation from Physiology to Pathology

Components of the Total Serum Thyroid Hormone Concentrations during Pregnancy: HighFree Thyroxine and Blunted Thyrotropin (TSH) Response to TSHReleasing Hormone in the First Trimester*

Thyroliberin and Gonadoliberin Tests During Pregnancy and the Puerperium

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