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The influence of hyperthyroidism on the hypothalamic-pituitary-gonadal axis
S Zähringer1, A Tomova, K von Werder
1Medizinische Klinik, Innenstadt, University of Munich, Germany.
Summary
This study found that while the hypothalamic-pituitary-gonadal (H-P-G) axis is functional in Graves' disease, it shows increased gonadotropin levels. Hyperthyroid men exhibit relative primary gonadal insufficiency, potentially linked to elevated sex-hormone binding globulin (SHBG).
Area of Science:
- Endocrinology
- Reproductive Medicine
Background:
- Graves' disease is a common autoimmune disorder affecting the thyroid gland.
- The hypothalamic-pituitary-gonadal (H-P-G) axis regulates reproductive function.
- Understanding H-P-G axis function in hyperthyroidism is crucial for managing reproductive health.
Purpose of the Study:
- To investigate the function of the H-P-G axis in patients with severe, untreated Graves' disease.
- To assess hormone profiles and pulsatility of gonadotropins and sex hormones.
- To determine if hyperthyroidism impacts H-P-G axis regulation and reproductive hormone balance.
Main Methods:
- Studied 7 male and 6 female healthy volunteers, and 7 male and 7 female patients with Graves' disease.
- Collected blood samples every 10 minutes for 8 hours to create hormone profiles.
- Measured luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin (PRL), testosterone (T), estradiol (E2), sex-hormone binding globulin (SHBG), and progesterone (P).
- Analyzed hormone pulsatility using Pulsar, Cluster, and Desade programs and assessed temporal relationships with concordance analysis.
- Utilized non-parametric statistics for data evaluation.
Main Results:
- Increased LH secretion in all hyperthyroid patients; FSH secretion increased only in hyperthyroid men.
- No significant differences in LH and FSH pulsatile characteristics between patients and controls.
- No change in prolactin (PRL) secretion.
- Significant copulsatility between LH and FSH, and LH and PRL, more pronounced in hyperthyroid subjects.
- Significantly increased plasma levels of steroid hormones and SHBG in hyperthyroid men, with a decreased Free Androgen Index.
Conclusions:
- The H-P-G axis function is not impaired in hyperthyroid patients, but gonadotropin levels are elevated.
- Hyperthyroid men may experience relative primary gonadal insufficiency, possibly due to elevated SHBG levels.
- The study confirmed the copulsatility of LH and FSH, and LH and PRL in both hyperthyroid patients and healthy individuals.
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