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Quantifying Agonist Activity at G Protein-coupled Receptors
Published on: December 26, 2011
Thyroid hormones decrease the affinity of 8-cyclopentyl-1,3-dipropylxanthine (CPX), a competitive antagonist, for the
Rudolf Gesztelyi1, Zsuzsa Kiss, Judit Zsuga
1Department of Pharmacology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary. gesztelyi.rudolf@pharm.unideb.hu
General Physiology and Biophysics
|December 21, 2012
Summary
Thyroxine treatment in guinea pigs reduced the affinity of the A1 adenosine receptor for the antagonist CPX. This change in receptor affinity partially explains the diminished A1 receptor-mediated effects observed in hyperthyroid states.
Area of Science:
- Pharmacology
- Cardiovascular Physiology
- Endocrinology
Background:
- Thyroxine (T4) is a key thyroid hormone regulating metabolism.
- Adenosine receptors, particularly the A1 subtype, play a role in cardiac function.
- Hyperthyroidism can alter cardiovascular responses and receptor sensitivity.
Purpose of the Study:
- To determine if thyroxine (T4) treatment affects the binding affinity (KB) of the antagonist CPX to the guinea pig atrial A1 adenosine receptor.
- To investigate the impact of T4 treatment on the inotropic response to adenosine receptor agonists in the presence of CPX.
Main Methods:
- Experiments were conducted on isolated guinea pig left atria from solvent- or T4-treated animals.
- Inotropic responses to adenosine or CPA were measured with and without the antagonist CPX.
- Schild analysis was used to calculate the equilibrium dissociation constant (KB) for the CPX-A1 receptor complex.
Main Results:
- Schild analysis was valid for CPA but not adenosine.
- The affinity of CPX for the A1 receptor was lower in T4-treated (hyperthyroid) guinea pigs (KB = 44.16 nM) compared to euthyroid controls (KB = 16.63 nM).
- Hyperthyroid atria showed a significant reduction in the negative inotropic effects of adenosine and CPA.
Conclusions:
- Thyroxine treatment leads to a moderate decrease in the affinity of the guinea pig atrial A1 adenosine receptor for the antagonist CPX.
- The reduced affinity of the A1 receptor contributes only partially to the diminished A1 receptor-mediated effects observed in hyperthyroidism.
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