Kazuhiko Nishi

AGE-RELATED CHANGES IN CONTRACTILE RESPONSES OF RABBIT LOWER URINARY TRACT TO ENDOTHELIN

PURPOSE As there are significant amounts of endothelin (ET) receptors in the mammalian urinary tract, we investigated the pharmacological properties and localization of ET receptors in the rabbit lower urinary tract as a function of age. MATERIALS AND METHODS The characteristics of ET receptors in bladder dome, trigone and urethra of 6 weeks and 6 months old male rabbits were determined using muscle bath and autoradiographic techniques. RESULTS ET-1 produces significant contractile responses in smooth muscle strips from bladder dome, trigone, and urethra in both 6 weeks and 6 months old rabbits. Although there was no significant difference in the maximum contractile response of urethral muscle strips to ET-1 between 6 weeks and 6 months old rabbits, the maximum responses to ET-1 were higher in both bladder dome and trigone of 6 weeks than 6 months old rabbits. A selective ETA receptor antagonist, BQ 610, shifted the concentration response curve to ET-1 to the right without decreasing maximal contractile responses in all regions from both age groups, whereas a selective ETB receptor antagonist, IRL 1038, had no significant effect on the contractile response in these tissues. Autoradiographic studies indicate that both ET receptor subtypes are expressed in bladder dome, trigone, and urethra with the ETA subtype being located only in the smooth muscle layers and the ETB subtype being located in both the urothelial and smooth muscle layers. CONCLUSION Our data indicate the presence of region- and age-dependent differences in the contractile properties of ET receptors in the male rabbit lower urinary tract. Although both ETA and ETB receptor subtypes are present in the smooth muscle layers, the ETA receptor is the sub-type that is primarily involved in the mediation of contractions.

Effect of experimental diabetes on rat prostate endothelin receptors

We studied the properties of endothelin receptors in the prostate of 8-week streptozotocin-diabetic and control rats. The density of endothelin receptors, as determined by saturation experiments with [125I]endothelin-1, were 95.8 +/- 5.4 and 171.3 +/- 16.7 fmol/mg of protein in control and diabetic rat prostates, respectively. The pharmacological profile of the endothelin receptors was similar in both groups and was consistent with the predominance of the endothelin ETA receptor subtype in the prostate. Thus, the induction of diabetes upregulates the expression of endothelin receptors in the rat prostate, but does not alter the pharmacological profile of the receptors in these tissues.

Gene expression, localization, and pharmacological characterization of endothelin receptors in diabetic rat bladder dome

As there are significant amounts of functional endothelin receptors in the mammalian urinary tract, we examined the effect of experimental diabetes on the expression of endothelin receptors and their mRNAs in the rat bladder dome. The density of endothelin receptors in the rat bladder dome was higher (8 and 16 weeks following the onset of diabetes) than in age-matched controls. Insulin treatment, started 8 weeks after the induction of diabetes, partially reversed the endothelin receptor alterations. The pharmacological profile of the endothelin receptors in the bladder dome was similar in all groups and was consistent with the predominance of the endothelin ET(A) receptor subtype (ET(A):ET(B)=approximately 4:1). Autoradiographic studies demonstrated that the endothelin receptors were located in all tissue components of the bladder, including epithelial and muscular layers. Semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) data indicated that diabetes increased the expression level of gene transcripts for both endothelin receptor subtypes and that insulin treatment reversed the mRNA upregulation.

Properties of Alpha-1-Adrenergic Receptors in the Rat Prostate: Effect of Experimental Diabetes

We studied the effects of 8 weeks of streptozotocin (STZ)-induced diabetes on the density and the pharmacological properties of α₁-adrenoceptors in the rat prostate using receptor-binding experiments with [¹²⁵I]iodo-2[β-(4-hydroxyphenyl)-ethylaminomethyl]tetralone [¹²⁵I]HEAT. Saturation experiments showed the presence of specific [¹²⁵I]HEAT-binding sites in the control and diabetic rat prostate and that the induction of diabetes significantly decreased the density of [¹²⁵I]HEAT-binding sites in the rat prostate. [¹²⁵I]HEAT-binding sites in the prostate of both groups were inhibited by prazosin (nonselective), spiperone (α_1B-selective), WB4101 and 5-methylurapidil (α_1A-selective) and BMY7378 (α_1D-selective) with the following rank order of K_i values: prazosin < WB4101 < 5-methylurapidil < spiperone < BMY7378, indicating a similar pharmacological profile of α₁-adrenoceptor in the 2 groups.Comparing the K_i values of the rat prostate with those obtained from the rat submaxillary gland (α_1A), rat spleen (α_1B), rat vas deferens (α_1A + α_1B) and those reported for cloned α_1D, indicates the predominance of the α_1A + α_1B or the α_1A subtype in the rat prostate. The present study demonstrates that STZ-induced diabetes downregulates the expression of α₁-adrenoceptor in the rat prostate, without significantly affecting the receptor subtype specificity.

Characterization of endothelin receptors in streptozotocin-induced diabetic rat vas deferens

As there is increasing evidence that diabetes induces changes in the plasma levels of endothelins (ETs) and in the properties of ET receptors in peripheral tissues, and as there are reports indicating the presence of significant amounts of ET receptors in mammalian vasa deferentia, we studied possible alterations in ET receptor characteristics in the vasa deferentia of the following groups of rats: 8 weeks diabetic (D8), 8 weeks age-matched control (C8), 16 weeks diabetic (D16), 16 weeks diabetic-insulin-treated (started 8 weeks after the onset of diabetes) (DI16), and 16 weeks age-matched control (C16). Diabetes was induced by the i.v. injection of 65 mg/kg streptozotocin (STZ). Diabetic rats had hyperglycemia, hypoinsulinemia, glucosuria, polydipsia, and polyuria and had smaller vasa deferentia than control and diabetic-insulin-treated animals. Receptor binding experiments with [125I]ET-1 demonstrated that the densities of ET receptors in vasa deferentia from D8, C8, D16, DI16, and C16 animals were 377 +/- 11, 255 +/- 24, 315 +/- 18, 210 +/- 12, and 214 +/- 7 fmol/mg of protein, respectively. [125I]ET-1 binding to the ET receptors was inhibited by ET-1 (non-selective), BQ 610 (ETA selective), ET-3 (ETC selective), and IRL 1620 (ETB selective) with the following rank order of Ki values: ET-1 < BQ 610 < ET-3 < < IRL 1620. The pharmacological profile of the ET receptors was similar in all groups and was consistent with the predominance of the ETA receptor subtype in the rat vasa deferentia. Our data indicate that experimental diabetes up-regulates the density of ET receptors in the rat vasa deferentia and that the receptor up-regulation is reversed by insulin treatment.

Experimental Diabetes Upregulates the Expression of Uretereral Endothelin Receptors

We investigated the binding characteristics of endothelin (ET) receptors in the ureters of rats with experimentally induced diabetes and diuresis. Receptor binding experiments demonstrated an upregulation in the expression of [125I]ET-1 binding sites in the diabetic rat ureter but not in the diuretic rat ureter. ET-1, ET-3, IRL 1620, and BQ 610 inhibited [125I]ET-binding to the rat ureter consistent with the predominance of ETA receptors in these tissues. The subtype specificity of ET receptors in ureteral tissues was confirmed with inhibition data obtained from cloned human ETA and ETB receptors.

Pharmacologic Actions of Temiverine (p-INN) and its Active Metabolite, RCC-36, on Isolated Human Urinary Bladder Muscle

Background: Temiverine (p‐INN) is a newly synthesized drug that is expected to have anticholinergic action. We investigated the pharmacologic actions of temiverine and its active metabolite, RCC‐36, on isolated human bladder.

Characterization, localization and distribution of alpha1 adrenoceptor subtype in male rabbit urethra.

PURPOSE The subtype specificity, localization and distribution of urethral alpha1-adrenoceptors were studied in the male rabbit urethra. MATERIALS AND METHODS The properties of the urethral alpha1-adrenoceptors were investigated using radioligand receptor binding and light microscopic autoradiography with [125I]iodo-2-[b-(4-hydroxyphenyl)-ethylaminomethyl]tetralone (HEAT), and immunohistochemistry with monoclonal anti-alpha smooth muscle actin and anti-alpha sarcomeric actin antibodies. RESULTS Saturation experiments with [125I]HEAT demonstrated the presence of significant amounts of a single high affinity binding site for alpha1 adrenoceptors in the male rabbit urethra. The pharmacological profile of the alpha1 adrenoceptors in rabbit urethra, determined by inhibition experiments with subtype selective alpha1 adrenoceptor antagonists, was characterized by the following rank order of potency of inhibition constants (Ki values): prazosin < or = WB 4101 < spiperone < 5-methylurapidil < BMY 7378. The pKi values for the rabbit urethra were correlated with the pKi values for rat spleen, submaxillary glands, and vas deferens and for those reported for cloned alpha1d receptors with correlation coefficients of 0.68, 0.929, 0.909, and 0.523, respectively. CONCLUSIONS The pharmacological characterization demonstrates the predominance of alpha1A or alpha1A + alpha1B adrenoceptor subtype(s) in male rabbit urethral smooth muscle. Furthermore, the autoradiographic and immunohistochemical studies show a heterogeneous distribution of alpha1 adrenoceptors along the longitudinal axis of the urethra, within the smooth muscle fibers, with the receptors being localized more densely in the proximal than in the distal urethra.