Kozo Hamada

Mechanisms of the Suppression of the Bladder Activity by Flavoxate

Background: This study was designed to clarify the primary site of action of flavoxate, clinically used for the treatment of urinary frequency.

NS-49, an α1A-adrenoceptor agonist, selectively increases intraurethral pressure in dogs

Abstract The effects of NS-49 (( R )-(−)-3′-(2-amino-1-hydroxyethyl)-4′-fluoromethane sulfonanilide hydrochloride), an α 1A -adrenoceptor-selective agonist, on intraurethral pressure and blood pressure were investigated in anesthetized dogs. In addition, the contractile effects of NS-49 on the isolated dog urethra and carotid artery were compared with those of non-selective α 1 -adrenoceptor agonists. Intravenously (i.v.) administered NS-49 at 0.3 μg/kg or more significantly increased intraurethral pressure in a dose-dependent manner. Much higher doses of NS-49 were needed to increase blood pressure. In contrast, ST-1059 (1-(2′,5′-dimethoxyphenyl)-2-aminoethanol) (an active metabolite of midodrine) at 30 μg/kg or more significantly increased both intraurethral pressure and blood pressure. NS-49 was 11-fold more selective for intraurethral pressure than ST-1059. NS-49, ST-1059, phenylephrine and noradrenaline caused concentration-dependent contraction of the isolated dog urethra. NS-49 caused only a slight contraction of the dog carotid artery even at high concentrations, whereas the reference drugs caused contractions of the artery with high efficacy. The α 1A -adrenoceptor-selective antagonists 5-methylurapidil and WB-4101 also showed high affinity for α 1 -adrenoceptors in the dog urethra in inhibiting [ 3 H]prazosin binding. In conclusion, the α 1A -selective agonist NS-49 selectively increased intraurethral presure in dogs, and produced selective contraction of the dog urethra. These results suggest that the α 1A -adrenoceptor subtype is responsible for the contraction of the urethra and the regulation of intraurethral pressure, and that NS-49 might be useful for the treatment of stress incontinence with little effect on the cardiovascular system.

Effects of castration on contraction and α1-adrenoceptor expression in rat prostate

The prostate function is regulated by androgens and α‐adrenergic activity. Clinically, antiandrogens and/or α1‐adrenergic antagonists are commonly used to treat symptomatic prostatic hypertrophy. To elucidate the effects of androgen deprivation on prostate contractility via α1‐adrenoceptor, the characteristics and expression of α1‐adrenoceptors were examined in castrated rats. Isolated prostate strips from intact and castrated rats were subjected to a phenylephrine stimulated contraction. Prazosin (10 nM), [3H]‐prazosin and phenoxybenzamine (3–300 nM) were used for inhibition assay, receptor characterization and partial alkylation of α‐adrenoceptor, respectively. The mRNA content of three subtypes of α‐adrenoceptors was determined by reverse transcription combined with polymerase chain reaction (RT–PCR). Contractile response to phenylephrine increased in castrated rats, which could be explained by a relative increase of the stromal component. A lowered contraction potency was also noted in castrated rats. Receptor binding assay indicated minimal changes in the affinity or density of α1‐adrenoceptor. Escalating alkylation of the α1‐adrenoceptor population resulted in a rightward shift in the contraction‐response curves before depressing maximal contractile force, and the suppression was detected at lower doses in castrated rats. RT–PCR study confirmed the expression of three types of α1‐adrenoceptor, α1a, α1b and α1d‐adrenoceptors, in intact rat prostate, and revealed that α1a‐adrenoceptor, but not α1b or α1d‐adrenoceptors, was down‐regulated in castrates. The results show that androgen deprivation suppressed α1‐adrenergic contractility of rat prostate strips, and the suppression was associated with down‐regulation of receptor reserve for the α1a‐adreneroceptor population expressed in intact rat prostate.

Density and Localization of Alpha1-Adrenoceptors in Hypertrophied Prostate

Alpha-adrenoceptors have been considered to play an important role in the regulation of the voiding force. In order to determine the density and localization of the alpha-adrenoceptors in the prostate, binding assays for alpha-adrenoceptors were performed with [3H]prazosin and [3H] yohimbine in membrane preparations from enucleated hyperplastic prostate tissues. Furthermore, autoradiographic analysis of alpha-adrenoceptors in the sliced tissue specimens from benign prostatic hypertrophy was performed. Specific binding of both ligands were saturable and of high affinity in membrane preparations, and Scatchard analyses indicated Bmax = 104 fmole/mg. protein, Kd = 0.488 nM for [3H]prazosin, and Bmax = 41 fmole/mg, protein, Kd = 1.83 nM for [3H] yohimbine. Bmax and Kd for [3H]prazosin were greater in the adenoma than in the submucosal tissue of the prostatic urethra. No relationship was noted between the size of enucleated prostate and the density of alpha-adrenoceptors. Image analysis of autoradiograms using [3H]prazosin showed specific binding sites could not be clearly demonstrated, but only [125I]HEAT slightly exposed specific binding sites in the prostate.

Effect of NS‐21, an Anticholinergic Drug with Calcium Antagonistic Activity, on Lower Urinary Tract Function in a Rat Model of Urinary Frequency

Background: NS‐21 is under development for the treatment of urinary frequency and urinary incontinence. The purpose of this study was to investigate the effects of NS‐21 and its active metabolite, RCC‐36, on lower urinary tract function in an experimental rat model of urinary frequency.

Quantitative autoradiography of α1 adrenoceptors with [3H]tamsulosin in human hypertrophied prostate using computerized image analysis

SummaryFourteen specimens of human hypertrophied prostate were evaluated for the distribution of α1 adrenoceptors using autoradiography with a computerized image analysis system. The hypertrophied prostatic specimens, obtained at open prostatectomy, were dissected vertically to the urethra, and sectioned at 10 μm. They were immersed in 1 nM of specific α1 ligand, [3H]tamsulosin chloride ([3H]tamsulosin) and exposed to autoradiographic film. The images were analysed by a computerized image analysis system. The total binding of [3H]tamsulosin in the whole section (n = 14) was 0.82 ± 0.21 (mean ± se) nCi mg−1. The autographic data were correlated with data obtained in a membrane-binding assay. The prostatic tissue studied was divided into urethral, glandular and stromal zones, the latter two zones being further divided into the inner and outer areas. The total binding of [3H]tamsulosin in the urethral zone (n = 7) was 0.65 ± 0.32 nCi mg−1. The glandular zone contained significantly more abundant α1 adrenoceptors than the stromal zone and their densities (glandular vs stromal) were 1.15 ± 0.19 nCi mg−1 (n = 14) vs 0.72 ± 0.15 nCi mg−1 (n = 14), respectively (p < 0.05). The data from the whole section were not affected by prostatic weight. This method described enabled the distribution of the receptors in different sites to be evaluated both morphologically and quantitatively.

CNS-mediated influence of TRH and its analog, NS-3, on the function of the rabbit lower urinary tract

The effects of thyrotropin-releasing hormone (TRH) and its new analog, NS-3 (montireline), on the lower urinary tract in rabbits were investigated. TRH and NS-3 elicited transient increases in intravesical pressure and micturition. They also caused long-lasting increases in intraurethral pressure and EMG activity of the external urethral sphincter, which were not affected by prazosin or transection of the hypogastric nerve, but were eliminated by transection of the pudendal nerve. In animals decerebrated at the supracollicular post-mammillary level, these drugs did not increase intravesical pressure or micturition, but they did elicit increases in intraurethral pressure and sphincter EMG activity. No binding sites for TRH were found in the lower urinary tract. These findings suggest that the sites of action of TRH and NS-3 which elicit intravesical pressure increase or micturition might be located in the area rostral to the pons, and that the sites of action which elicit increases in intraurethral pressure and sphincter EMG activity might be located caudal to the rostral pons.

Renal aging change of α1-adrenoceptor in wistar rats

Abstract 1. 1. The aging changes of density of the α 1 -adrenoceptors in the kidney were evaluated with Wistar rats of several ages (8, 52 and 104 weeks old). 2. 2. [ 3 H]prazosin and [ 3 H]YM617 (newly synthesized α 1 -blocker) were used for the ligand. The B max of [ 3 H]prazosin was 74.0 ± 9.5 fmol/mg/protein in 8 week, 52.1 ± 7.3 fmol/mg protein in 52 week, and 31.3 ± 4.2 fmol/mg/protein in 104 week rats, and that of [ 3 H]YM617 was 45.0 ± 6.6 fmol/mg/protein in 8 week, 32.4 ± 5.7 fmol/mg/protein in 52 week, and 19.3 ± 5.5 fmol/mg/protein in 104 week rats. 3. 3. The B max of both ligands for 104 week rats was significantly decreased compared to 8 week rats, however, 52 week rats showed no decrease of B max for both ligands. 4. 4. The K d values showed no difference in these three age groups for both ligands. 5. 5. Autoradiographic study supported the result above mentioned. Furthermore, the binding sites of α 1 -adrenoceptors were mainly in the cortex (vascular wall and peritubular area) and that α 1 -adrenoceptors were chiefly chlorethylclonidine dihydrochloride (CEC) insensitive.