J Korean Med Sci.  1999 Feb;14(1):69-74. 10.3346/jkms.1999.14.1.69.

Comparison of relaxation responses of cavernous and trigonal smooth muscles from rabbits by alpha1-adrenoceptor antagonists; prazosin, terazosin, doxazosin, and tamsulosin

• Seo KK
• Lee MY
• Lim SW
• Kim SC

• KMID: 1062200
• DOI: http://doi.org/10.3346/jkms.1999.14.1.69

Abstract

Alpha1a-adrenergic receptor (AR) primarily mediates the contraction of the prostatic and cavernous smooth muscles. Among clinically available alpha1-AR antagonists for the medical management of benign prostatic hyperplasia (BPH), tamsulosin has a modest selectivity for alpha1A- and alpha1D- over alpha1B-ARs. To compare the effects of various alpha1-AR antagonists on relaxation responses of cavernous and trigonal smooth muscles, isometric tension studies with relatively selective (tamsulosin) and non-selective (prazosin, doxazosin, and terazosin) alpha1A-AR antagonists, were conducted in the cavernous and trigonal muscle strips of rabbits (n=10 each). Tamsulosin had the strongest inhibitory effect on contraction of trigonal smooth muscle among the various alpha1-AR antagonists, and the inhibitory activities of prazosin, doxazosin, and terazosin were not statistically different. All alpha1-AR antagonists caused concentration-dependent relaxation of the cavernous muscle strips. Tamsulosin was shown to have greater potency than prazosin (more than 100-fold), doxazosin (more than 1000-fold), and terazosin (more than 1000-fold), in relaxation of cavernous smooth muscle. In conclusion, tamsulosin might be the most effective drug among the four commonly used alpha1-AR antagonists for the medical management of BPH. Tamsulosin might be a potential substitute for phentolamine in combination with vasoactive agents as an intracavernous injection therapy for patients with erectile dysfunction.

Keyword

alpha1-Adrenergic alpha-eceptor antagonist; Muscle smooth cavernous; Bladder, trigone; Relaxation

MeSH Terms

Adrenergic alpha-Antagonists/pharmacology*
Animal
Comparative Study
Doxazosin/pharmacology*
In Vitro
Muscle Contraction/drug effects
Muscle Relaxation/drug effects*
Muscle, Smooth/physiology
Muscle, Smooth/drug effects*
Prazosin/pharmacology*
Rabbits
Receptors, Adrenergic, alpha-1/antagonists & inhibitors*
Sulfonamides/pharmacology*