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Tamsulosin: alpha1-adrenoceptor subtype-selectivity and comparison with terazosin
I Muramatsu1, T Taniguchi, K Okada
1Department of Pharmacology, School of Medicine, Fukui Medical University, Matsuoka, Japan.
Japanese Journal of Pharmacology
|December 30, 1998
Summary
Tamsulosin and terazosin selectively target alpha1-adrenoceptor subtypes. Tamsulosin shows higher affinity for alpha1A and alpha1L subtypes, while terazosin is more selective for alpha1D, particularly in the human prostate.
Area of Science:
- Pharmacology
- Adrenergic Receptor Research
- Urology
Background:
- Alpha1-adrenoceptors mediate various physiological functions, including smooth muscle contraction.
- Tamsulosin and terazosin are alpha-blockers used clinically, but their subtype selectivity profiles require detailed understanding.
- Understanding adrenoceptor subtype selectivity is crucial for optimizing drug efficacy and minimizing side effects.
Purpose of the Study:
- To compare the selectivity profiles of tamsulosin and terazosin against different functional alpha1-adrenoceptor subtypes.
- To investigate the binding affinities of these drugs to cloned and native alpha1-adrenoceptor subtypes.
- To determine the relative affinity of tamsulosin and terazosin in the human prostate.
Main Methods:
- Competitive inhibition assays were used to assess the functional blockade of noradrenaline-induced contractile responses.
- Binding studies were performed using cloned human (alpha1a, alpha1b, alpha1d) and native (alpha1A, alpha1B) adrenoceptor subtypes.
- Drug affinities were quantified in both functional and binding assays, with a specific focus on the human prostate.
Main Results:
- Both tamsulosin and terazosin competitively inhibited responses mediated by alpha1D, alpha1B, and alpha1L subtypes.
- Tamsulosin exhibited selectivity for alpha1A > alpha1L and alpha1D > alpha1B subtypes.
- Terazosin demonstrated lower overall affinity but showed notable selectivity for the alpha1D-subtype. Tamsulosin displayed over 30-fold higher affinity than terazosin in the human prostate.
Conclusions:
- Tamsulosin and terazosin possess distinct selectivity profiles for alpha1-adrenoceptor subtypes.
- Tamsulosin demonstrates a preference for alpha1A and alpha1L, while terazosin shows greater selectivity for alpha1D.
- The significantly higher affinity of tamsulosin in the human prostate suggests a potential basis for its clinical efficacy in conditions like benign prostatic hyperplasia.