Dopamine D1 and D2 receptors in the human ureter and urinary bladder: a radioligand binding and autoradiographic study

Design, synthesis and in vitro evaluation of a Dopa-organoboron compound that acts as a bladder relaxant through non-catecholamine receptors

Bladder relaxation through drug administration is an interesting topic in medicinal and combinatorial chemistry. In fact, compounds targeting catecholamine receptors [dopamine receptors and beta-adrenergic receptors (βAR) expressed in the bladder] are among the compounds commonly employed for this purpose. In particular, recent investigations have tended to focus on the β₃-adrenoceptor (β₃AR) as a target in the treatment of urinary incontinence and other disorders. However, organoboron compounds have been suggested as potent and efficient agents on these drug targets. In this work, through a docking study, we identified the parameters that induce a theoretical improvement in the affinity and activity of the organoboron compounds on the catecholamine receptors expressed in the bladder. Then, the identified potential drug, a boron-containing dopa-derivative named DPBX-L-Dopa, was synthesized and characterized. This compound induces a relaxation on the smooth muscle of the rat bladder, behaving as a weak relaxant compared to isoproterenol but with similar efficacy to BRL377, a selective β₃AR agonist. However, unexpectedly, this effect was not blocked by propranolol or haloperidol at the concentrations at which they are able to block the catecholamine receptors in bladder tissue. In view of these results, the effect of DPBX-L-Dopa compound on the alpha 1 adrenergic receptors (α₁AR) of aorta of the rats was also explored; however, no response of the tissue to this compound was obtained. The possible mechanisms of the action of this compound were explored and are discussed further.

Design, synthesis and in vitro evaluation of a Dopa-organoboron compound that acts as a bladder relaxant through non-catecholamine receptors

Bladder relaxation through drug administration is an interesting topic in medicinal and combinatorial chemistry. In fact, compounds targeting catecholamine receptors [dopamine receptors and beta-adrenergic receptors (βAR) expressed in the bladder] are among the compounds commonly employed for this purpose. In particular, recent investigations have tended to focus on the β₃-adrenoceptor (β₃AR) as a target in the treatment of urinary incontinence and other disorders. However, organoboron compounds have been suggested as potent and efficient agents on these drug targets. In this work, through a docking study, we identified the parameters that induce a theoretical improvement in the affinity and activity of the organoboron compounds on the catecholamine receptors expressed in the bladder. Then, the identified potential drug, a boron-containing dopa-derivative named DPBX-L-Dopa, was synthesized and characterized. This compound induces a relaxation on the smooth muscle of the rat bladder, behaving as a weak relaxant compared to isoproterenol but with similar efficacy to BRL377, a selective β₃AR agonist. However, unexpectedly, this effect was not blocked by propranolol or haloperidol at the concentrations at which they are able to block the catecholamine receptors in bladder tissue. In view of these results, the effect of DPBX-L-Dopa compound on the alpha 1 adrenergic receptors (α₁AR) of aorta of the rats was also explored; however, no response of the tissue to this compound was obtained. The possible mechanisms of the action of this compound were explored and are discussed further.

Molecular and pharmacological detection of dopaminergic receptors in the human male urinary tract

AIMS

Evidence indicates that dopamine (DA) and DA receptors play a role in the central nervous system (CNS) control of micturition; however, while the central DAergic role in the micturition physiology has been extensively investigated, the expression and the function of DA receptors in the urinary tract are still under investigation. Here, we studied the distribution of DA receptor subtypes in different parts of the human male urinary tract.

METHODS

Fragments were collected from 34 men. The mRNAs encoding DA receptors were assessed by RT-PCR, followed by densitometric analysis. Adenylyl cyclase (AC) activity was evaluated using a commercially available RIA kit. Statistical analysis was carried out using one-way ANOVA, with the Bonferroni's post hoc test.

RESULTS

Results obtained indicated that RT-PCR products of D(1), D(4), and D(5) subtypes were obtained in each part studied, while no signal was observed for the D(2) and D(3) receptor subtypes. The pharmacological characterization demonstrated that the expressed DA receptors were linked to AC.

CONCLUSIONS

DA receptors were expressed throughout the human male urinary tract, from the ureter to the prostatic urethra. In particular, we observed a distinctive DA receptor subtype distribution, with evidence of the presence of mRNA encoding both subtypes of the D(1)-like DA receptor family (D(1) and D(5)), while the D(4) receptors were the only expressed subtype of the D(2)-like family. These results suggested that DAergic drugs used for the treatment of a number of diseases may influence the micturition physiology not only in the CNS, but at the peripheral level as well.

[Ureter drugs]

Many improvements have been made recently in the field of the ureteral smooth muscle pharmacology. After a brief summary on physiological basis, we review what is known about effects on ureter of different drugs class. In a second part, we review clinical applications for renal colic analgesia, calculi expulsive medical therapy, ESWL adjuvant treatment and preoperative treatment before retrograde access. There are now sufficient data on NSAID and alpha-blockers. beta-agonists, especially for beta3 selective ones, and topical drugs before retrograde access are interesting and should be further evaluated.

Impact of Functional Age on the Use of Dopamine Agonists in Patients With Parkinson Disease

BACKGROUND

Parkinson disease (PD) is primarily a neurodegenerative disorder that affects as many as 1,500,000 people in the United States. It is predominantly a disease of the elderly, and special treatment challenges must be addressed in this patient population.

REVIEW SUMMARY

It has been generally accepted that PD patients over the age of 70 will have a shorter lifespan than younger patients and are at less risk for developing treatment-emergent complications by virtue of their lower exposure to medication over the course of the disease. Consequently, elderly patients are often treated aggressively when motor symptoms start to become disabling. Recent statistics, however, suggest that effective treatments for PD have helped to increase the longevity of PD patients, suggesting that elderly patients may, in fact, have sufficient medication exposure to raise concern over levodopa-induced motor complications. If this is the case, physicians should consider treating their elderly PD patients with dopamine agonists, which have several advantages over levodopa therapy, not the least of which is a lower prevalence of motor complications.

CONCLUSION

Dopamine agonists are safe and effective in elderly patients and offer numerous advantages when used as either monotherapy or adjunctive therapy, particularly in patients requiring long-term treatment.

Effects of dopaminergic treatment on bladder function in Parkinson's disease

AIMS

To evaluate the nature of voiding complaints, findings on urodynamics and the effects of medication on bladder control in a group of Parkinson's disease (PD) patients between the ages of 30-60 years.

METHODS

Thirty-two patients with PD were evaluated by questionnaires, PD rating scales, and full urodynamics evaluation. To evaluate lower urinary tract symptoms (LUTS), we used the Danish Prostate Symptom Score (Dan-PSS). PD was evaluated using Unified Parkinson's Disease Rating Scale (UPDRS), and Hoehn and Yahr rating scale for PD. Urodynamics were performed while the patients were on dopaminergic therapy, and after stopping this for three half lives.

RESULTS

There was a significant correlation between the Dan-PSS score and UPDRS, Spearman's rho = 0.50, (P = 0.004), and between the score of irritative symptoms in Dan-PSS and motor symptoms (UPDRS(III)) is seen (Spearman's rho = 0.50, P = 0.003). Patients with significant bladder symptoms (> or =10 points in Dan-PSS) had a significantly higher bladder capacity in the medicated state than after wash out (P = 0.04), while patients with out bladder symptoms had no difference. Patients with a significant increase in bladder capacity on medication had a significantly higher interval between the volume of first sensation of bladder filling and bladder capacity when medicated (P = 0.01) than after wash out. Patient who did not benefit from medication had a significant lower interval off medication (P = 0.008).

CONCLUSIONS

The effects of dopaminergic treatment on bladder control and urodynamic parameters are unpredictable in the individual patient, though most patients experience significant changes. We have also demonstrated the complexity of bladder control, and that patients with PD may be particularly susceptible to develop complex micturitional dysfunction. Our data indicates that cortical dysfunction may play a significant role in bladder dysfunction in PD parallel to the pontine lesion.

Localization of peripheral dopamine D1 and D2 receptors in rat corpus cavernosum

OBJECTIVE

To detect and locate anatomically peripheral dopamine D1 and D2 receptors in rat cavernosa, as dopamine is important in sexual drive and penile erection through receptors located in the central nervous system.

MATERIALS AND METHODS

Corpora cavernosa were obtained from Sprague-Dawley rats; total RNA and membrane proteins were extracted and cryostat sections prepared. The rat brain hypothalamus was used as a control for dopamine D1 and D2 receptors. The presence and expression of peripheral dopamine D1 and D2 receptor mRNAs in rat corpus cavernosa was assessed using reverse transcription and polymerase chain reaction (RT-PCR), and Northern blot hybridization using (32)P-UTP-labelled RNA probes. Concurrently, corresponding proteins from D1 and D2 receptors were assayed and detected by a Western blotting technique. The anatomical location of dopamine D1 and D2 receptor mRNAs in rat penile tissues was identified by in situ hybridization using (35)S-UTP-labelled RNA probes in cryostat sections. Immunohistochemical staining was used to locate peripheral dopamine D1 and D2 receptor proteins in rat corpora cavernosa.

RESULTS

Dopamine D1 and D2 receptor gene expression was detected in rat corpora cavernosa. In situ hybridization signals for dopamine D1 and D2 receptor mRNAs were localized to corpus cavernosal tissues and dorsal vessels in the rat penis. Western blot analyses showed peripheral dopamine D1 and D2 receptor proteins in rat corpora cavernosa. Immunohistochemically, peripheral dopamine D1 and D2 receptor proteins were detected in dorsal nerves, dorsal vessels and corpus cavernosal smooth muscle of the rat penile tissues.

CONCLUSIONS

Peripheral dopamine D1 and D2 receptors are present in the corpora cavernosa of rats. The functional significance of these receptors and signal transduction pathways in modulating the vascular tone of the penis warrants further investigation.

Determination of dopamine D1 receptors in the human uveo scleral tissue by light microscope autoradiography

The aim of this paper is to clarify the distribution of Dopamine D1 (DA D1) receptors in the uveo-scleral tissue of human eyes with or without elevated intraocular pressure (IOP) and to study the relationships between DA D1 receptors and uveo-scleral tissue. Samples of human uveo-scleral tissue were taken from seven men undergoing eye surgery for a traumatic lesion of the anterior segment of the eye, without involvement of the iris-corneal angle and /or from eye donors. The subjects (in whom one eye bulb had been surgically enucleated) had been previously enrolled in our medical protocols because they suffered for increased IOP, while the eye donors (of both eye bulbs) had a normal IOP. Frozen sections from the uveo-scleral tissue were submitted to biochemical characterization and to morphological autoradiographic techniques for detection of DA-D1 receptors. [3H]-SCH-23390 was used as a ligand of Dopamine D1 receptors. [3H]-SCH 23390 was bound by sections of the human uveo-scleral tissue. The pharmacological profile of the binding was consistent with the labeling of D1 receptors. Light microscope analysis was used for localization of D1 receptors and revealed an accumulation of the radioligand in the human uveo-scleral tissue. In eyes with normal IOP there is a high reaction. The Bmax of radioligand decreases in the eyes with increased IOP. The possibility that dopaminergic receptors play a role in the controlling uveo-scleral tissue functions is suggested.

Effects of spinal alpha 1-adrenoceptor antagonism on bladder activity induced by apomorphine in conscious rats with and without bladder outlet obstruction

To test the hypothesis that the spinal control of micturition involves alpha 1-adrenoceptors, the urodynamic effects of intrathecal and intraarterial alpha 1-adrenoceptor blockade on apomorphine-induced bladder activity in rats were studied. Continuous cystometry was performed in conscious female Sprague-Dawley rats with and without bladder outflow obstruction. In normal rats, subcutaneous apomorphine, 30 micrograms/kg, induced bladder activity that was abolished or attenuated by the alpha 1-adrenoceptor antagonists indoramin and doxazosin given intrathecally or intra-arterially. In rats with outlet obstruction, apomorphine 30 micrograms/kg caused no change in cystometric parameters. However, at a dose of 100 micrograms/kg the drug induced bladder activity, which was attenuated by intrathecal indoramin or doxazosin. These results suggest that the bladder activity evoked by apomorphine-stimulation of bulbospinal pathways can be influenced by alpha 1-adrenoceptors at the spinal and peripheral levels, both in normal rats and in rats with bladder hypertrophy secondary to outlet obstruction.

Neurological disorders of micturition and their treatment

An overview of the current concepts of the neurological control of the bladder is given, based on laboratory experiments and PET scanning studies in human subjects. This is followed by a description of the various causes of the neurogenic bladder, discussed in a hierarchical order starting with cortical lesions and descending through the basal ganglia and brainstem, spinal cord, conus and cauda equina to disorders of peripheral innervation. Then follows a description of the condition of isolated urinary retention in young women. The article concludes with a review of the methods available for treating neurogenic bladder disorders. These are largely medical but brief mention of appropriate surgical procedures is made.