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Related Experiment Videos

Circulating thyrotropin bioactivity in sporadic central hypothyroidism.

L Persani1, E Ferretti, S Borgato

  • 1Institute of Endocrine Sciences, University of Milan, Istituto Auxologico Italiano Instituto di Ricovero e Cura a Carattere Scientifico, Italy. persani@auxologico.it

The Journal of Clinical Endocrinology and Metabolism
|November 4, 2000
PubMed
Summary

Central hypothyroidism (CH) involves pituitary and hypothalamic issues. This study found that patients with CH commonly secrete thyroid-stimulating hormone (TSH) with reduced bioactivity, contributing to the condition alongside impaired pituitary TSH reserve.

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Area of Science:

  • Endocrinology
  • Molecular Biology
  • Pathophysiology

Background:

  • Central hypothyroidism (CH) stems from pituitary or hypothalamic lesions.
  • Pituitary CH (pCH) involves reduced thyrotropes and TSH secretion quantity.
  • Hypothalamic CH (hCH) presents with normal/high TSH and altered TSH bioactivity.

Purpose of the Study:

  • To investigate the occurrence and characteristics of bioinactive TSH in CH patients.
  • To differentiate the roles of pituitary TSH reserve and TSH bioactivity in CH pathogenesis.
  • To explore the relationship between TSH bioactivity and clinical/biochemical parameters in CH.

Main Methods:

  • Studied 41 CH patients with diverse hypothalamic-pituitary disorders.
  • Assessed immunoreactive TSH (TSH-I), free T4 (FT4), and free T3 (FT3) levels.

Related Experiment Videos

  • Measured TSH bioactivity using bioassays and ricin affinity chromatography, calculating the TSH biological (B)/immunological (I) ratio.

    • Main Results:

    • A blunted TSH response to TRH (indicating pCH) was observed in 56% of patients.
    • A significant correlation was found between TSH increments and basal FT4 levels.
    • The TSH B/I ratio was significantly reduced in CH patients compared to controls, with no difference between pCH and hCH.
    • Reduced TSH bioactivity correlated significantly with FT3 response to TRH-stimulated TSH.

    Conclusions:

    • Secretion of TSH molecules with reduced bioactivity is a common finding in patients with hypothalamic-pituitary lesions.
    • Impaired pituitary TSH reserve and reduced TSH bioactivity both contribute to the pathogenesis of CH.
    • Elevated sialylation of TSH molecules may partly explain the reduced bioactivity observed.