Age-dependent changes in particulate and soluble guanylyl cyclase activities in urinary tract smooth muscle

Regional and age specific differences are observed in the sodium nitroprusside induced relaxation responses in the urinary tract. To clarify these differences, guanylyl cyclase activity is assayed in particulate and soluble fractions from the ureter, bladder dome, and urethra of young (11-18 days), adult (90-100 days), and old adult (2-3 years) guinea pigs. The rank order of soluble guanylyl cyclase activities is urethra = ureter > bladder dome with the largest decreases with aging occurring in the bladder. Atrial natriuretic factor (10(7) M) increases particulate guanylyl cyclase activity in the three tissues at all ages tested, with the activity being highest in the ureter. ATP (0.5 mM) activates particulate guanylyl cyclase in the ureter, bladder and urethra of old adult guinea pigs, and enhances atrial natriuretic factor induced activation of particulate guanylyl cyclase in all tissues and at all ages tested. The higher levels of soluble guanylyl cyclase activity in the urethra and ureter compared to the bladder parallel sodium nitroprusside induced relaxation in these tissues.

Involvement of nitric oxide and cyclic GMP in rabbit urethral relaxation

Soluble and particulate fractions from rabbit urethra converted [14C]arginine to [14C]citrulline, indicating the presence of nitric oxide synthase activity in these fractions. Both soluble and particulate nitric oxide synthase activities were NADPH dependent, and the soluble activity was Ca2+ dependent. Three nitric oxide synthase (NOS) inhibitors affected transmural nerve stimulation induced relaxation responses in the rabbit urethra and the activity of soluble nitric oxide synthase with the same rank order of potency, i.e., NG-nitro-L-arginine (NNA) > NG-methyl-L-arginine (NMA) > canavanine (CAN). The rank order of potency with respect to particulate NOS activity was CAN > NMA = NNA. The relaxation responses to electrical stimulation were accompanied by increases in cyclic GMP. These results suggest that NOS activity found in the soluble fraction of urethral homogenates produces nitric oxide that in turn increases cyclic GMP levels which mediates the relaxation responses induced by transmural nerve stimulation in the rabbit urethra.

The reversal effect of insulin on diabetes-induced alterations in beta adrenergic and muscarinic receptors in rat prostate

Previous studies from our laboratory demonstrated that 8 weeks after the induction of diabetes by the administration of streptozotocin (STZ) there was a downregulation of beta adrenergic and muscarinic cholinergic receptors in rat prostate, and that early insulin treatment (started 3 days after the onset of diabetes) prevented these alterations from occurring. In the present study, the effects of later insulin treatment (started 8 weeks after the onset of diabetes) on the reversibility of diabetes-induced alterations in beta adrenergic and muscarinic receptors in rat prostate were investigated. Three groups of rats were maintained for 16 weeks: 1) diabetics, 2) insulin-treated diabetics (subcutaneously injected with 5 to 8 U per day starting 8 weeks after the onset of diabetes) and 3) age matched controls. Binding studies with [3H]dihydroalprenolol (DHA) and [3H]quinuclidinyl benzilate (QNB) showed a significantly lower density of beta adrenergic and muscarinic cholinergic receptors in the diabetic rat prostate than in prostate from either controls or insulin-treated diabetic animals. Inhibition of [3H]DHA binding by isoproterenol, a beta adrenergic agonist, and binding of [3H]QNB by carbachol, a muscarinic agonist, indicated the presence of low and high affinity agonist binding sites for each receptor. The relative proportion of high affinity to total binding sites as well as the low and high affinity constants were similar in all groups. These data indicate that insulin treatment, begun 8 weeks after the onset of diabetes, can reverse the diabetes-induced downregulation of both beta adrenergic and muscarinic cholinergic receptors in STZ-diabetic rat prostates.

[Experimental studies of urinary incontinence. Effect of tiropramide on the urinary stage and evacuation]

Tiropramide, a tyrosine derivative, has an antispasmodic effect on the gastrointestinal smooth muscles and it is suggested that the effect is mediated by cAMP. Therefore, we studied the effects of tiropramide on the lower urinary tract smooth muscle functions. In animal experiments, the effects of tiropramide on vesicourethral smooth muscle contraction were investigated and cAMP and cGMP levels following tiropramide administration were measured in the vesicourethral and gastrointestinal smooth muscles. In clinical trials, five healthy volunteers and five patients with neurogenic bladder dysfunction were treated orally with tiropramide 300 mg a day for two weeks and examined for urodynamic parameters before and after tiropramide treatment. Tiropramide significantly inhibited contraction of the vesicourethral smooth muscle and the inhibitory effect upon the bladder was remarkable particularly at the lower concentrations. Tiropramide remarkably increased cAMP level but it had no effect on cGMP level in the bladder at the lower concentrations. Tiropramide at the lower concentrations did not affect cAMP and cGMP levels in the smooth muscles of the urethra, stomach and intestines. In the patients with neurogenic bladder dysfunction treated with tiropramide orally, the urine volume at first desire to void and maximum bladder capacity increased significantly, but the volume of residual urine did not significantly increase. In the healthy volunteers, there were no significant changes in urodynamic parameters. These findings indicate that tiropramide relaxes the urinary bladder smooth muscle via cAMP to increase the urinary bladder capacity.

Regional difference in functional roles of cAMP and cGMP in lower urinary tract smooth muscle contractility

The spontaneous contractile force of muscle strips isolated from rabbit urinary bladder dome, base and urethra was dose-dependently inhibited by isoproterenol, an adenylate cyclase activator through beta-adrenoceptors and also by sodium nitroprusside, a guanylate cyclase activator. The relaxation response by isoproterenol was biggest in urinary bladder dome. Percent relaxation to 10(-4) M isoproterenol was 73.6% in bladder dome, 56.1% in bladder base, and 44.1% in urethra. The relaxation response by nitroprusside was biggest in urethra. Percent relaxation to 10(-4) M sodium nitroprusside was 34.8% in bladder dome, 51.2% in bladder base, and 63.2% in urethra. Cyclic adenosine monophosphate (cAMP) accumulation by isoproterenol was greatest in dome. cAMP levels increased by 150% in bladder dome, by 74% in bladder base and by 80% in urethra after 1 min over basal levels to become stable for 5 min. Cyclic guanosine monophosphate (cGMP) accumulation by sodium nitroprusside was greatest in urethra. cGMP levels increased by 445% in urethra after 1 min over basal levels and by 320% in dome, by 380% in base and by 1,100% in urethra after 5 min over basal levels. Dibutyryl cAMP relaxed the dome, base and urethra. 8-bromo cGMP also relaxed them. These results suggest that the role of cGMP is mainly related to urethral relaxation, whereas the role of cAMP is mainly related to urinary bladder relaxation.

NG-nitro-L-arginine inhibits non-adrenergic, non-cholinergic relaxation in rabbit urethral smooth muscle

Electrical field stimulation induced a relaxation response in female rabbit urethral smooth muscle strips precontracted with phenylephrine. The relaxation response was inhibited by tetrodotoxin, but not by atropine, propranolol, or hexamethonium. The relaxation response thus results from stimulation of inhibitory non-adrenergic, non-cholinergic nerves. The electrically induced relaxation response was inhibited by an inhibitor of nitric oxide biosynthesis, NG-nitro-L-arginine. This inhibition was overcome by addition of a precursor of nitric oxide, L-arginine. An inhibitor of soluble guanylate cyclase, methylene blue, reduced the relaxation response, and a selective cyclic GMP phosphodiesterase inhibitor, M & B 22948, potentiated the relaxation response. These data indicate that agents which affect the biosynthesis of nitric oxide are associated with the urethral relaxation response evoked by electrical field stimulation, and that cyclic GMP may mediate the relaxation response.

[Functional roles of cyclic AMP and cyclic GMP on rabbit urinary bladder and urethral smooth muscle contraction]

It is suggested that cyclic AMP and cyclic GMP play regulatory roles in smooth muscle function. In order to clarify the role of cyclic AMP and cyclic GMP in the function of the lower urinary tract, I examined the effects of isoproterenol and sodium nitroprusside on contractile force and tissue content of cyclic AMP and cyclic GMP. Isoproterenol (10(-8)-10(-4) M) caused a relaxing effect in the rabbit urinary bladder dome, the bladder base and the urethra. The relaxation response by isoproterenol was mediated by cyclic AMP. The relaxation response and the increase in the cyclic AMP level were marked in the bladder dome. Sodium nitroprusside (10(-8)-10(-4) M) also caused a relaxing effect in the rabbit urinary bladder dome, the bladder base and the urethra. The relaxation response to sodium nitroprusside was mediated by cyclic GMP. The relaxation response and the increase in the cyclic GMP level were marked in the urethra. The external addition of derivatives of cyclic AMP and cyclic GMP (dibutyryl cyclic AMP and 8-bromo cyclic GMP, 10(-8)-10(-3) M) also caused a relaxing effect in the bladder dome, the bladder base and the urethra. These results demonstrated that both cyclic AMP and cyclic GMP were related to relaxation of the rabbit lower urinary tract smooth muscle. It seems that cyclic AMP may be mainly related to relaxation of the bladder dome and cyclic GMP may be mainly related to relaxation of the urethra.