Inhibition by tamsulosin of tension responses of human hyperplastic prostate to electrical field stimulation.
Tamsulosin (10(-10)-10(-9) M) or prazosin (10(-9)-10(-8) M) concentration dependently blocked the tension responses to electrical field stimulation (0.3 ms duration, 80 V and 20 Hz) in human hyperplastic prostate with lC50 values of (1.93 +/- 0.26) x 10(-10) M and (2.11 +/- 0.21) x 10(-9) M, respectively. The relative potency of tamsulosin with reference to prazosin was 10.96. The pA2 values for tamsulosin and prazosin against phenylephrine-induced contractions were 10.05 +/- 0.16 and 9.25 +/- 0.07, respectively. The relative potency of tamsulosin with reference to prazosin was 6.31. In the presence of prazosin to block alpha 1-adrenoceptor-mediated responses, nifedipine (10(-5) M), but not tamsulosin (10(-9) M), significantly blocked the tension responses in human hyperplastic prostate induced by increasing [Ca2+]o concentrations (10(-4) to 3 x 10(-3) M) in a Ca(2+)-free environment pre-depolarized with 60 mM K+. Additionally, the effects of prazosin and tamsulosin on electrical field stimulation-evoked [3H]noradrenaline release were studied on the S3/S2 ratios. It appeared that both drugs had little effect on this release reaction, with S3/S2 ratios of 0.96 +/- 0.02 and 0.90 +/- 0.02, respectively. These results indicate that tamsulosin is a potent antagonist against endogenous sympathetic stimulation in human hyperplastic prostate.
Chueh
S C
SC
Department of Urology, College of Medicine, National Taiwan University, Taipei.
Guh
J H
JH
Chen
J
J
Lai
M K
MK
Ko
F N
FN
Teng
C M
CM
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000368:Aged; D002121:Calcium Channel Blockers / Q000494:pharmacology; D004558:Electric Stimulation; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000503:physiopathology; D009543:Nifedipine / Q000494:pharmacology; D009638:Norepinephrine / Q000378:metabolism; D010656:Phenylephrine / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D011467:Prostate / Q000187:drug effects / Q000378:metabolism / Q000503:physiopathology*; D011470:Prostatic Hyperplasia / Q000378:metabolism / Q000503:physiopathology*; D013449:Sulfonamides / Q000494:pharmacology*; D000077409:Tamsulosin
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D002121:Calcium Channel Blockers; D013449:Sulfonamides; D010656:Phenylephrine; D000077409:Tamsulosin; D009543:Nifedipine; D011188:Potassium; D009638:Norepinephrine; D011224:Prazosin