Mechanisms Of The Decrease In Vesical Micturition Pressure Induced By Doxazosin And Its Enantiomers In Animals

Benign prostatic hyperplasia (BPH) often leads to lower urinary tract symptoms (LUTS). Patients with BPH/LUTS are suffering serious troubles on the quality of life. racemic-Doxazosin (rac-DOX),a long acting selectiveα1-adrenoceptor antagonist, is the current medication for the clinical treatment of BPH/LUTS. Several clinical studies have demonstrated that rac-DOX produces a decrease in urethral resistance and improve in lower urinary tract symptoms by blockingα1-adrenoceptor. However, rac-DOX is limited in the clinical application for BPH/LUTS due to its common adverse effects of dizziness, headache, and orthostatic hypotension. Therefore, the urinary tract selectivity should be necessarily considered whenα1-adrenoceptor antagonists are used for the BPH/LUTS patients.rac-DOX is a mixture of S-doxazosin (S-DOX) and R-doxazosin (R-DOX). In a pharmacological study using the human isolated prostate tissue, S-DOX, R-DOX and rac-DOX all competitively antagonized the phenylephrine-induced contractile responses without significant differences in the pA2 values among S-DOX, R-DOX and rac-DOX. Recently, a study in our laboratory showed that the effects of S-DOX on animal blood pressure and onα1-adrenoceptors of the isolated rabbit blood vessels were significantly weaker than rac-DOX and R-DOX. However,the inhibitory effect by S-DOX on vesical micturition pressure was same to rac-DOX. To investigate the mechanisms of decreasing vesical micturition pressure by doxazosin and its enantiomers in animals, we observed the effects of S-DOX, R-DOX and rac-DOX on the contractile responses to drugs and electric field stimulation in the isolated rabbit urinary bladder detrusor, prostate and urethral strips, and the effects of S-DOX, R-DOX and rac-DOX on the prostate cell proliferation and apoptosis in the aged mouse. PartⅠEffects of doxazosin and its enantiomers on the contractile responses in the isolated rabbit urinary detrusor stripsContractile responses to drugs or electric field stimulation in the dorsal and ventral detrusor strips of the isolated rabbit urinary bladder were recorded to study the effects of S-DOX, R-DOX and rac-DOX on the contractile responses.1 Contractile responses to carbachol and phenylephrine in the dorsal and ventral detrusor strips of the isolated rabbit urinary bladderCarbachol produced contractile responses concentration-dependently in the dorsal and ventral detrusor strips, and the concentration-response curves for carbachol in the two kinds of strips were not significantly different from each other. Phenylephrine induced contractile responses in a concentration-dependent manner in the dorsal detrusor strips but not in the ventral detrusor strips.2 Effects of doxazosin and its enantiomers on the contractile responses to phenylephrine in the dorsal detrusor strips of the isolated rabbit urinary bladderPhenylephrine produced contractile responses concentration-dependently in the dorsal detrusor strips, and solvent had no effect on the contractile responses. The pKB values of S-DOX, R-DOX and rac-DOX at 1μmol·L^-1 against phenylephrine in the dorsal detrusor strips of the isolated rabbit urinary bladder were 7.44±0.19, 7.39±0.14 and 7.38±0.30, respectively, and the pKB values of doxazosin and its enantiomers were not significantly different from each other (P>0.05).3 Effects of doxazosin and its enantiomers on the contractile responses to electric field stimulation in the dorsal and ventral detrusor strips of the isolated rabbit urinary bladderElectric field stimulation produced a steady contractile responses those were completely inhibited by tetrodotoxin (TTX) at 0.1μmol·L^-1. S-DOX, R-DOX and rac-DOX significantly inhibited the contractile responses to electric field stimulation in the dorsal detrusor strips of the isolated rabbit urinary bladder (P<0.05), and their inhibitory effects were not significantly different from each other (P>0.05). However, S-DOX, R-DOX and rac-DOX did not affect the responses to electric field stimulation in the ventral detrusor strips.These results indicate that S-DOX, R-DOX and rac-DOX significantly inhibit the contractile responses to electric field stimulation in the dorsal detrusor strips of the isolated rabbit urinary bladder via postsynapticα?1-adrenoceptors, and S-DOX inhibits the responses to the same extent as R-DOX and rac-DOX.PartⅡEffects of doxazosin and its enantiomers on contractile responses in the isolated rabbit prostate stripsContractile responses to drugs or electric field stimulation were recorded to study the effects of S-DOX, R-DOX and rac-DOX on the contractile responses in the isolated rabbit prostate strips.1 Effects of doxazosin and its enantiomers on the contractile responses to phenylephrine in the isolated rabbit prostate stripsPhenylephrine produced contractile responses concentration-dependently in the prostate strips, and solvent did not affect the contractile responses. S-DOX, R-DOX and rac-DOX at 0.01μmol·L^-1 and 0.03μmol·L^-1 produced parallel shift of the cumulative concentration-response curves (CCRCs) for phenylephrine to the right in the isolated rabbit prostate, and the values of Emax of CCRCs for phenylephrine were not changed significantly by S-DOX, R-DOX and rac-DOX (P>0.05). The Schild plot analysis indicated that S-DOX, R-DOX and rac-DOX competitively antagonized the phenylephrine-induced contractile responses in the isolated rabbit prostate strips. The pA2 values of S-DOX, R-DOX and rac-DOX were 8.22±0.03, 8.25±0.03 and 8.20±0.04, respectively, and the pA2 values of three agents were not significantly different from each other (P>0.05).2 Effects of doxazosin and its enantiomers on the contractile responses to electric field stimulation in the isolated rabbit prostate stripsElectric field stimulation produced a steady contractile responses, and the responses were completely inhibited by TTX at 0.1μmol·L^-1. S-DOX, R-DOX and rac-DOX significantly inhibited the contractile responses to electric field stimulation in the isolated rabbit prostate strips (P<0.01), and S-DOX inhibited the responses to the same extent as R-DOX and rac-DOX.3 Effects of atropine, phentolamine and PPADS on the contractile responses to electric field stimulation in the isolated rabbit prostate stripsAtropine (1μmol·L^-1) significantly reduced the contractile responses to electric field stimulation by 62.6±11.7%, and co-application with 10μmol·L^-1 phetolamine abolished the contractile responses to electric field stimulation. Phetolamine (10μmol·L^-1) alone markedly reduced the contractile responses to electric field stimulation by 96.7±9.3%, and co-application with 1μmol·L^-1 atropine abolished the contractile responses to electric field stimulation. PPADS (10μmol·L^-1) failed to affect the contraction induced by electric field stimulation in the isolated rabbit prostate strips (P>0.05). TTX (0.1μmol·L^-1) abolished the contractile responses.These results indicate that doxazosin and its enantiomers significantly inhibit the contractile responses to electric field stimulation via postsynapticα1-adrenoceptors in the isolated rabbit prostate strips. The pA2 values of doxazosin and its enantiomers against phenylephrine are not significantly different from each other in the isolated rabbit prostate strips.PartⅢEffects of doxazosin and its enantiomers on the contractile responses in the isolated rabbit urethral stripsIn the urinary bladder neck strip and proximal, medial and distal urethral strips of the rabbit, the contractile responses to drugs and electric field stimulation were recorded. The effects of S-DOX, R-DOX and rac-DOX on the contractile responses to phenylephrine in the urinary bladdr neck strip and proximal, medial and distal urethral strips were observed. The pharmacological prolife of contractile responses to electric field stimulation in the urethral strips were investigated.1 Effects of doxazosin and its enantiomers on the contractile responses to phenylephrine in the isolated rabbit urinary bladder neck strip and urethral stripsPhenylephrine produced contractile responses concentration-dependently in the isolated rabbit urinary bladder neck strip and the urethral strips, and solvent did not affect the contractile responses (P>0.05). The pKB values of S-DOX, R-DOX and rac-DOX against phenylephrine in the bladder neck were 7.88±0.23, 7.92±0.11 and 7.87±0.10, respectively, and the pKB values of the three agents were not significantly different from each other (P>0.05). The pKB values of doxazosin and its enantiomers against phenylephrine were not significantly different in the proximal, medial and distal urethral strips.2 Effects of rac-DOX on the contractile responses to electric field stimulation in the isolated rabbit urinary bladder neck strip and proximal, medial and distal urethral stripsSolvent did not affect the frequency-response curves for electric field stimulation in the isolated rabbit urinary bladder neck strip and urethral strips. rac-DOX (0.01-1μmol·L^-1) was ineffective against the contractions induced by electric field stimulation in the isolated urinary bladder neck strip and proximal, medial and distal urethral strips, even though TTX at 0.1μmol·L^-1 completely inhibited the responses.3 Effects of prazosin, atropine and indomethacin on the contractile responses to electric field stimulation in the isolated rabbit urinary bladder neck strip and proximal, medial and distal urethral stripsSolvent did not affect the frequency-response curves for electric field stimulation in the isolated rabbit urinary bladder neck strip and urethral strips. Prazosin (1μmol·L^-1) was ineffective against the contractile responses to electric field stimulation (P>0.05), while atropine (1μmol·L^-1) significantly reduced the contractions (P<0.01). Co-application of prazosin and atropine caused an inhibition to the same extent as atropine alone (P>0.05). A treatment with the combination of prazosin, atropine and indomethacin decreased the contractile responses more potently than a treatment with a combination of prazosin and atropine (P<0.01). In the proximal, medial and distal urethral strips of the rabbit, prazosin, atropine or indomethacin did not affect the contractile responses to electric field stimulation, even though TTX at 0.1μmol·L^-1 abolished the responses.4 Effects of atropine, phentolamine, tubocurarine, nicotine, suramin and tetrodotoxin on the contractile responses to electric field stimulation in the isolated rabbit urethral stripsElectric field stimulation produced a steady contractile response in the isolated rabbit urethral strips. Atropine (0.1-3μmol·L^-1) or phentolamine (1-30μmol·L^-1) did not affect the contraction induced by electric field stimulation in the isolated rabbit urethral strips. Tubocurarine significantly inhibited the contraction at 0.01μmol·L^-1 and 0.03μmol·L^-1 by 11.4±6.2% and 52.1±14.8%, respectively. Nicotine at 10μmol·L^-1 significantly inhibited the contraction by 53.7±14.9%. Suramin at 10, 30 and 100μmol·L^-1 significantly inhibited the contraction by 22.5±3.5%, 33.8±5.3% and 54.2±5.9%, respectively.Tubocurarine (0.1μmol·L^-1), Nicotine (30μmol·L^-1) and TTX (0.1μmol·L^-1) abolished the contractile responses to electric field stimulation in the isolated rabbit urethral strips. 5 Responses of the isolated rabbit urethral strips to carbachol, moxonidine, clonidine, adenosine, ATP, UTP, 5-HT and histamineMoxonidine (10μmol·L^-1) and clonidine (10μmol·L^-1) produced small contractions in the isolated rabbit urethral strips, and the contractile force was 0.20±0.12g and 0.11±0.05g, respectively. Carbachol (30μmol·L-1), adenosine (30μmol·L^-1), ATP (10μmol·L^-1), UTP (30μmol·L^-1), 5-HT (3μmol·L^-1) and histamine (30μmol·L^-1) could not produce any contractile responses in the urethral strips.These results indicate that doxazosin and its enantiomers antagonize the phenylephrine-induced contractile responses in the isolated rabbit urinary bladder neck strips and proximal, medial and distal urethral strips via postsynapticα1-adrenoceptors, and the pKB values of doxazosin and its enantiomers are not significantly different from each other.Neurogenic contractile responses to electric field stimulation are motor neuron-evoked contractions with characteristics of highly sensitive to nicotine and suramine, and the neurogenic contractions are not affected by rac-DOX and prazosin.PartⅣEffects of doxazosin and its enantiomers on the volume and cell proliferation of the prostate in aged mouseThe male mouse at 13 months of age was used to study the effects of long-term (12 weeks) intragastrical administration of doxazosin and its enantiomers on the volume and wet weight of the prostate, and the effects on the cell proliferation and apoptosis of the anterior lobe prostatic cells in aged mouse.1 Effects of doxazosin and its enantiomers on the volume and wet weight of the prostate in aged mouseIn comparison with young mouse, the volume index of the prostate in aged mouse did not change significantly (P>0.05), but the volume index of the prostate in aged mouse treated with S-DOX (6.0mg·kg-1), R-DOX (6.0mg·kg-1), R-DOX (0.6mg·kg-1) or rac-DOX (6.0mg·kg-1) was significantly decreased (P<0.05).2 Effects of doxazosin and its enantiomers on the cell cycle, proliferation and apoptosis of the anterior lobe cells of the prostate in aged mouseIn comparison with young mouse, the total G0/G1-phase of the cells of the anterior lobe of the prostate were significantly decreased (P<0.01), and the total G2/M-phase cells of the anterior lobe of the prostate and the proliferation index of the prostatic cells were significantly increased in aged mouse (P<0.01).In comparison with aged mouse, the proliferation index and cell cycle distribution of the anterior prostatic lobe in aged mouse treated by S-DOX, R-DOX and rac-DOX did not change significantly (P>0.05).These results indicate that doxazosin and its enantiomers slightly decrease the volume index of the prostate in aged mouse by long-term intragastrical administration. ConclusionThe inhibitory effects by S-DOX on cardiovascular system are significantly weaker than those by rac-DOX and R-DOX, while S-DOX inhibits the vesical micturition pressure to the same extent as rac-DOX. Results of the present study suggest that a decrease in vesical micturition pressure induced by S-DOX is related to the reduction in contractile responses to electric field stimulation via its blocking action on the postsynapticα1-adrenoceptors in the urinary bladder detrusor smooth muscle and prostate smooth muscle, and S-DOX has the same affinity forα1-adrenoceptors as R-DOX in the isolated rabbit urinary bladder detrusor smooth muscle and prostate smooth muscle.S-DOX, R-DOX and rac-DOX inhibit theα1-adrenoceptor activity to the same extent in the isolated rabbit urethral strips. However,α1-adrenoceptor antagonists of rac-DOX and prazosin are not able to affect the neurogenic contractions induced by electric field stimulation in the urethral strips. Neurogenic contractile responses to electric field stimulation in the isolated rabbit urethral strips are motor neuron-evoked contractions with characteristics of highly sensitive to nicotine and suramine.