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[Loss of high-affinity prostacyclin binding sites in patients with Basedow's disease]
I Virgolini1, K Weiss, M Hermann
1Atheroskleroseforschungsgruppe (ASF) Wien.
Abstract:
Prostacyclin (PGI2) mediates like TSH its cellular effects through the interaction with specific binding sites associated with the adenylate cyclase-cAMP-system. Binding of PGI2 and the generation of cAMP induced by PGI2 was evaluated in thyroid tissue obtained intraoperatively from euthyroid and hyperthyroid patients with diffuse normofollicular colloid struma. Transformation of the binding data according to Scatchard revealed heterogeneity of the PGI2 binding sites in the tissue of euthyroid patients: the high-affinity binding sites were calculated to be 0.68 +/- 0.18 pmol/mg protein (Ka = 16.2 +/- 9.1 nM) and the low-affinity binding sites to be 5.4 +/- 1.6 pmol/mg protein (Ka = 151 +/- 43.1 nM). In contrast, in the hyperthyroid patients the low-affinity binding sites were not demonstrable and the high-affinity sites were significantly (p less than 0.001) reduced (0.17 +/- 0.05 pmol/mg protein, Ka = 83.5 +/- 19.6 nM). The competition of the agonist for the PGI2 sites in hyperthyroid patients was significantly (p less than 0.005) diminished (IC-50-values: 0.98 +/- 3.1 vs 46.9 +/- 12.1 microM). PGI2 stimulated cAMP-production in a dose-dependent manner. However, the basal value was significantly lower also in the hyperthyroid patients (p less than 0.001). The evidence of reduced PGI2 sites as well as reduced PGI2-induced cAMP production in the thyroid gland of patients with Graves' disease may indicate an important role for PGI2 to play in the modulation of thyroid cell function.
Insights
Prostacyclin (PGI2) signaling is altered in hyperthyroid patients, with fewer binding sites and reduced cAMP production in thyroid tissue. This suggests PGI2 plays a role in modulating thyroid cell function in Graves' disease.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Signaling
Context:
- Prostacyclin (PGI2) mediates cellular effects via adenylate cyclase-cAMP system, similar to TSH.
- Thyroid tissue from euthyroid and hyperthyroid patients with diffuse normofollicular colloid struma was analyzed.
- PGI2 binding and cAMP generation were evaluated in these tissues.
Purpose:
- To investigate the characteristics of PGI2 binding sites in thyroid tissue from euthyroid and hyperthyroid patients.
- To assess the impact of hyperthyroidism on PGI2-induced cAMP production.
- To explore the potential role of PGI2 in modulating thyroid cell function in Graves' disease.
Summary:
- Scatchard analysis revealed heterogeneous PGI2 binding sites in euthyroid patients (high-affinity: 0.68 ± 0.18 pmol/mg protein, Ka = 16.2 ± 9.1 nM; low-affinity: 5.4 ± 1.6 pmol/mg protein, Ka = 151 ± 43.1 nM).
- Hyperthyroid patients showed significantly reduced high-affinity PGI2 sites (0.17 ± 0.05 pmol/mg protein, Ka = 83.5 ± 19.6 nM) and diminished agonist competition (IC-50: 0.98 ± 3.1 vs 46.9 ± 12.1 μM).
- PGI2 dose-dependently stimulated cAMP production, but basal levels were significantly lower in hyperthyroid patients, indicating impaired PGI2 signaling.
Impact:
- Findings suggest reduced PGI2 binding sites and diminished PGI2-induced cAMP production in the thyroid gland of patients with Graves' disease.
- This may indicate a significant role for prostacyclin in the modulation of thyroid cell function.
- Further research into PGI2's role could offer new therapeutic targets for thyroid disorders.