Supersensitivity of the Rat Urinary Bladder Following »Chemical Sympathectomy«

Local Change in Urinary Bladder Contractility Following CNS Dopamine Denervation in the 6-OHDA Rat Model of Parkinson's Disease

BACKGROUND

Urinary problems, including urinary frequency, urgency, and nocturia are some of the non-motor symptoms that correlate most with poor quality of life in Parkinson's disease. However, the mechanism behind these symptoms is poorly understood, in particular regarding peripheral bladder pathophysiology following dopamine degeneration.

OBJECTIVE

In this study, we compared the contractile responsiveness of urinary bladder from the 6-OHDA unilateral rat model of Parkinson's disease with that of normal untreated animals.

METHODS

The contractility of the urinary detrusor muscle was evaluated in bladder strip preparations using electrical field stimulation, and muscarinic and purinoceptor stimulations in an vitro organ bath setup.

RESULTS

Our data show that the overall contractile response following electrical field stimulation was significantly higher (43% at maximum contraction by 20-40 Hz stimulation) in the 6-OHDA-lesioned rats as compared to control animals. This increase was associated with a significant increase in the cholinergic contractile response, where the muscarinic agonist methacholine produced a 44% (at 10 -4 M concentration) higher response in the 6-OHDA-treated rats as compared to controls with a significant left-shift of the dose response. This indicates an altered sensitivity of the muscarinic receptor system following the specific central 6-OHDA-induced dopamine depletion. In addition a 36% larger contraction of strips from the 6-OHDA animals was also observed with purinoceptor activation using the agonist ATP (5×10 -3 M) during atropine treatment.

CONCLUSIONS

Our data shows that it is not only the central dopamine control of the micturition reflex that is altered in Parkinson's disease, but also the local contractile function of the urinary bladder. The current study draws attention to a mechanism of urinary dysfunction in Parkinson's disease that has previously not been described.

Augmentation of rat urinary bladder relaxation mediated by beta1-adrenoceptors in experimental diabetes

We examined how diabetes affects the beta-adrenoceptor subtypes mediating relaxation of rat urinary bladder smooth muscle contracted with carbachol. The relaxant responses to isoproterenol were larger in muscles from rats 8 to 10 weeks after induction of diabetes with streptozotocin (80 mg/kg, i.p.) as compared to the control muscles. In contrast, forskolin-induced relaxations did not differ significantly in the control and diabetes groups. Propranolol (1 microM) abolished the diabetes-induced augmentation of relaxant responses to isoproterenol. The relaxant responses to T-0509 ((-)-(R)-1-(3,4-dihydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)-amino]ethanol hydrochloride), a beta(1)-adrenoceptor agonist, were small but significantly augmented by diabetes. On the other hand, diabetes did not change the relaxations produced by clenbuterol, a beta(2)-adrenoceptor agonist, and BRL37344 ((+/-)-(R*,R*)-(4-[2-([2-(3-chlorophenyl)-2-hydroxyethyl]amino)propyl]phenoxy)acetic acid), a beta(3)-adrenoceptor agonist. These results suggest that diabetes selectively augments the beta(1)-adrenoceptor-mediated relaxation of the rat urinary bladder smooth muscle.

Denervation supersensitivity of the rabbit urinary bladder to calcium ion

We investigated in vitro the supersensitivity of denervated rabbit bladder to Ca2+. Seven days after denervation achieved by bilateral sacral rhizotomy, the capacity of the denervated bladder increased by 2.2 times as compared with the control (126.3 to 277.3 ml.), and wet weight also increased 4.3 times (3.6 to 15.3 gm.). After 30 minutes incubation in normal Krebs' solution the denervated bladder strips showed significantly increased amplitude of contractions to the cumulative acetylcholine addition than the control. After incubation in normal Krebs' solution for 30 minutes, muscle strips were washed three times with Ca-free Krebs' solution and incubated 30 minutes in this solution. Cumulative Ca2+ replenishment (0.5 to 10 mM) induced dose-dependent contractions of the detrusor muscle strips in Ca2+-free Krebs' solution, where the contractions were significantly stronger in the denervated detrusor muscle than in controls. Pretreatment with 10(-6) M verapamil (Ca-entry blocker) eliminated the enhanced Ca2+-induced contractions of the denervated detrusor strips, while 10(-6) M procaine (Ca-induced Ca releasing blocker) only partially inhibited them. After depolarizing the cell membrane with 40 mM KCl, the Ca2+-induced contractions of the control strips were markedly enhanced but those of the denervated strips were not. These results demonstrate the supersensitivity of the denervated detrusor muscle to Ca2+. We conclude that hyperpermeability of the cell membrane to Ca2+ influx through calcium channels is responsible for supersensitivity of the denervated detrusor muscle to Ca2+.

Micturition in the unanesthetized rat: effects of intrathecal capsaicin, N-vanillylnonanamide, 6-hydroxydopamine and 5,6-dihydroxytryptamine

Unanesthetized rats chronically implanted with vesical and intrathecal catheters were injected intrathecally (i.t.) with either capsaicin (CAP), N-vanillylnonanamide (VN), 6-hydroxydopamine (6-OHDA), or 5,6-dihydroxytryptamine (5,6-DHT). The volume-evoked micturition reflex was assessed by cystometrography before, and 2 h, 1 day and 7 days after injection. In control and vehicle-injected rats, the infusion of saline into the bladder resulted in a periodic contraction of the bladder with synergic sphincter relaxation. One day after i.t. CAP and VN (70 micrograms each), 50% and 30% of the animals displayed a blockade of the micturition reflex, respectively. In these animals, the infusion of saline resulted in a gradual rise in bladder pressure up to a plateau (overflow pressure) equivalent to the predrug bladder opening pressure. When the plateau was reached, continuous dribbling of urine with no bladder contractions was observed. Most of the affected rats displayed some micturition responses by day 7. Following i.t. injection of 5,6-DHT (20 micrograms) or 6-OHDA (20 micrograms), the micturition reflex displayed small but significant increases in bladder volume with no changes in pressure profile. Small primary afferents, sensitive to the neurotoxic effects of CAP and VN appear to play a major tonic role in the regulation of the micturition reflex in unanesthetized rats. Serotonergic and adrenergic descending pathways might play a role in the maintenance of resting bladder tone.

Origin and distribution of neuropeptide Y-, vasoactive intestinal polypeptide-and substance P-containing nerve fibers in the urinary bladder of the rat

The origin and distribution in the urinary bladder of nerve fibers containing neuropeptide Y (NPY), vasoactive intestinal polypeptide (VIP) and substance P (SP) were investigated in rats. Experimental procedures comprised preganglionic decentralization or postganglionic denervation of the bladder and also chemical sympathectomy as well as capsaicin treatment of newborn rats. Nerve fibers containing NPY were richly distributed in the detrusor muscle and also in the pelvic ganglia. Numerous NPY-containing nerve cell bodies were found in pelvic ganglia. A rich occurrence of VIP fibers and a more sparse distribution of SP-containing fibers were also found in the bladder as well as a relatively rich representation of VIP-containing nerve cell bodies in the pelvic ganglia. After decentralization the intensity of VIP and NPY immunofluorescence increased in nerve cell bodies of the pelvic ganglia and in nerve fibers in the wall of the bladder. Postganglionic denervation, on the other hand, eliminated all peptides examined in the bladder wall. After postganglionic denervation the situation in the ganglia was approximately the same as after decentralization. Chemical sympathectomy (6-OHDA) did not seem to change significantly the frequency and distribution of VIP-, SP- and NPY-fibers in the muscle layer of the bladder or in the pelvic ganglia, while the NPY-containing nerve fibers in the submucosal layer and around blood vessels of the bladder disappeared. Adrenergic nerve fibers in the wall of the bladder (visualized by histofluorescence) were markedly reduced in number after administration of 6-OHDA.(ABSTRACT TRUNCATED AT 250 WORDS)

On a cholinergic motor innervation of the rat urethra

Choline acetyltransferase activity was demonstrated in the proximal part of the male rat urethra, indicating a cholinergic innervation of this tissue. The cholinergic nerve fibres emanated evidently from the pelvic nerves, since bilateral removal of the pelvic ganglion caused a major fall in the activity of this enzyme. The muscle activity of the circular layer of the proximal urethra was recorded in vitro. The basal activity of this segment was low. The parasympathomimetics acetylcholine and methacholine, evoked rapid and marked contractile responses; the maximal responses to these drugs were 36 and 44%, respectively, of that to potassium. The corresponding figures for phenylephrine and noradrenaline were found to be 79 and 88%, respectively. The responses evoked by the parasympathomimetics were unaffected by the ganglion blocker hexamethonium, the alpha-adrenoceptor blocker dihydroergotamine and the beta-adrenoceptor blocker propranolol. Atropine, however, abolished the responses completely. Following degeneration of adrenergic or cholinergic nerves of the urethra the parasympathomimetics still evoked contractions. Taken together these findings indicate that the parasympathomimetics exert their contractile effect through a direct action on muscarinic receptors. Parasympathectomy but not sympathectomy (caused by 6-hydroxydopamine treatment) gave rise to a supersensitivity to methacholine, as judged by a leftward shift of the dose-response curve for this drug, the ED50-value being ten times less than that of the controls. The observations seem to suggest that the proximal urethra normally is under the influence of cholinergic activity beside that of adrenergic activity previously demonstrated.

Changes in sensitivity to the inhibitory effects of adrenergic agonists on intestinal motor activity after chronic sympathetic denervation

The concentration-effect relationships of adrenergic agonists in inhibiting muscular tone, carbachol-induced contraction of circular muscle strips and nerve-mediated motor activity during the peristaltic reflex have been studied in intact and sympathetically denervated preparations of isolated guinea-pig colon. The order of potencies of adrenergic agonists was different for muscular and nerve-mediated effects, being clonidine greater than noradrenaline greater than methoxamine greater than isoprenaline for the inhibition of peristalsis and isoprenaline greater than noradrenaline greater than methoxamine greater than clonidine for the relaxation of circular muscle. Denervation supersensitivity was specific for the adrenergic agonists and developed both to the muscular and nerve-mediated effects, involving both alpha and beta receptors. The degree of potentiation was similar for noradrenaline and isoprenaline when measured for the muscular effects but was significantly higher for noradrenaline than for isoprenaline or methoxamine when measured for peristalsis inhibition. No potentiation could be observed for papaverine and for the muscular effects of methoxamine and phenylephrine. The increase in potency of noradrenaline ranged from a 26-fold increase for the inhibition of propulsion velocity to a 2.5-fold increase for the inhibition of carbachol-induced contraction. A much narrower range was observed for isoprenaline. Potentiation could also be observed for the inhibitory effect of noradrenaline on acetylcholine release. Clonidine was the most potent agonist against peristaltic reflex and the weakest agonist in relaxing circular muscle. Denervated preparations became subsensitive to the inhibitory effect of clonidine on peristaltic reflex. The potency of clonidine relative to noradrenaline was 488 in intact preparations and only 3.1 in denervated organs.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible use of indoramin in patients with chronic neurogenic bladder dysfunction

Indoramin, which has great selectivity for alpha-1-receptors, was administered orally for 10 days to 21 patients with urinary retention or residual urine caused by neurogenic vesicourethral dysfunction. After indoramin therapy 17 patients were able to empty the bladder with residual urine less than 50 ml. There was a significant decrease in the maximum urethral pressure (23.87 plus or minus 4.13 cm. water) and in the functional profile length (0.53 plus or minus 0.19 cm.). A diminution in the sphincter electromyography activity was observed in 3 patients. Two paraplegics who were investigated during spinal shock could not achieve voiding after indoramin therapy. However, involuntary urine leakage associated with a change of posture occurred in 2 patients but subsided after the dosage of indoramin was decreased. No other side effect was observed. It may be desirable to use drugs with selective action upon alpha-1-receptors since blockade of noradrenergic autoreceptors (alpha-2) also by nonspecific alpha-adrenoceptor blocking agents, namely phentolamine, phenoxybenzamine and so forth, causes the overflow of norepinephrine, which would produce symptoms such as tachycardia by stimulating beta-receptors.

Supersensitivity in the isolated urethra of the rat following "chemical sympathectomy"

The circular muscle activity of the urethra of the male rat was isometrically measured in vitro in response to noradrenaline, phenylephrine and isoprenaline. The urethra was found to be supplied with both alpha- and beta-adrenoceptors mediating contraction and relaxation, respectively. The substance 6-hydroxydopamine is known to cause a selective destruction of adrenergic nerves. In the present study 6-hydroxydopamine (100 mg/kg) was injected intravenously into a group of rats twice with a weekly interval. When the urethra was examined 2-3 weeks after the first injection a supersensitivity mediated both via alpha- and beta-adrenoceptors was found to have developed, suggesting that the urethra of the male rat normally is under the influence of adrenergic activity. The findings are discussed in relation to denervation supersensitivity of the neurogenic bladder in man.

Growth of sympathetic postganglionic axons after partial chemical destruction with guanethidine

Partial sympathectomy of neonatal rats was produced by treatment with guanethidine. The number of neurons of the superior cervical ganglion decreased to 15% of control values and remained constant throughout the subsequent observation period of 4 months. The volume of the remaining neuronal perikarya increased faster than that of control animals during the observation period, and the density of adrenergic innervation of the iris and the noradrenaline content of the heart were found to partially recover after the initial decrease produced by the guanethidine treatment, reaching 33% and 30% of control values, respectively, after 4 months. The noradrenaline content of the duct of the vas deferens was greatly reduced by guanethidine treatment, but almost recovered after 4 months. The frequency of sympathetic preganglionic impulses was elevated throughout the 4 months observation period, and it is suggested that this increase is responsible for the compensatory changes in cell volume, terminal density and terminal noradrenaline content of the remaining neurons.

Compensatory increase of responses to nerve stimulation of the partially denervated rat urinary bladder

The rat urinary bladder was deprived of half of its innervation by removing the pelvic ganglion on one side. The motor response of such a partially denervated bladder to stimulation of the pelvic nerve on the other side were examined 1 week, 1 month and 2 months postoperatively. On all three occasions the increase in pressure of the operated bladder was larger than that of the control bladder; the enlargement was most marked 2 months after operation. The responses were further enlarged by eserine, and markedly reduced by atropine. The present results combined with those of previous investigations, showing a rapid recovery in the activity of the acetylcholine forming enzyme from a reduced level and a transient supersensitivity to chemical stimuli after unilateral removal of the pelvic ganglion, suggest that the enlarged responses to nerve stimulation 1 week postoperatively are mainly due to sensitization, while those observed at the later stages are due to collateral sprouting from the cholinergic nerve fibres of the intact pelvic nerve.

Salivary secretion evoked by H80/62, (+/-)-1-(4-hydroxyphenoxy)-3-isopropylamino-2-propranol, a new beta 1-selective adrenoceptor agonist

H80/62, recently introduced as a beta 1-selective adrenoceptor agonist, caused a long-lasting flow of saliva from parotid and submaxillary glands of the rat. The effect of H80/62 was prevented by propranolol or a beta 1-selective blocker. The drug did not exert its effect via the sympathetic postganglionic nerves; and it was not taken up by the neuronal amine pump. Sympathetically decentralized or denervated glands acquired a supersensitivity of the postjunctional type to H80/62.

Sensitization of the submaxillary gland of the rat after sympathetic denervation

The sensitivity of the submaxillary gland of the rat to chemical stimuli was examined 1, 4 and 6 weeks after sympathetic denervation. The gland was found to have developed a supersensitivity not only to noradrenaline but also, in contrast to previous reports, to adrenaline and methacholine. The supersensitivity remained unaltered throughout the period of observation.