Bladder Pharmacology Campbell-Walsh Ch. 56: 1948-1972

1. Bladder PharmacologyCampbell-WalshCh. 56: 1948-1972 Stephen Miller, DO

2. Peripheral Pharmacology

3. Muscarinic • 4 different receptor subtypes based on Pharmacology (M1-M5) • Human Bladder • M1 • M2 (Predominate) • M3: • Mediate cholinergic contractions • Key roles in: • Salivary secretion • Pupillary constriction • Digestive tract

4. M3R Action • Acetylcholine  M3R  IP3 hydrolysis (PLC)  Intracellular Ca2+ Release = Smooth Muscle Contraction • L- type Ca2+ channels have also been indicated in M3R mediated detrusor contractions

6. M2R • Coactivation could enhance response to M3: • Inhibition of adenylate cyclase = suppressing sympathetic mediated depression of detrusor • Inactivation of K+ channels • Activation of nonspecific cation channels

7. Prejunctional Muscarinic Receptors • M1R facilitate Acetylcholine release • M2-M4R inhibit release

8. Purinergic Mechanisms • Parasympathetic stimulation • ATP acts on 2 Receptors • P2X (ion channel) with 7 subtypes • P2Y (G-Protein coupled receptor) with eight subtypes • May play a role in Pathological conditions • Unstable bladders • BOO • Increased amount of P2X1R in obstructed bladders • P2X3R in small diameter afferent neurons of the DRG are also found in the wall of bladder and ureter • Mechanosensory and Nociceptive signaling

9. Adrenergic Mechanisms • Isoproterenol, Terbutiline • β- Adrenergic • β2 and β3 Receptors results in direct relaxation of detrusor smooth muscle •  3 main receptor • Mediated through stimulation of Adenylate cyclase and accumulation of cyclic AMP • PDE inhibitors? • Selective inhibition of bladder PDE  Increase cAMP • Relax detrusor and/or enhance the sensitivity/efficacy of  adrenergic agonists • Bladder Isoform of PDE?

10. -Adrenergic • Ephedrine, Phenylpropanolamine, Midodrine, Psuedoephedrine Bladder: (Not prominate in nml bladder) • -adrenergic density is increased in pathological conditions • NE induced responses convert from relaxation to contraction • 1dR subtype Urethra: • Promote urine storage by increasing Urethral resistance • Hypogastic nerve stimulation and -adrenergic agonists produce a rise in intraurethral pressure • blocked by 1- adrenergic antagonists • 1a major subtype in Urethra/Prostate

11. Nitric Oxide • Major inhibitory transmitter mediating relaxation of the urethral smooth muscle during micturation • Involved in controlling bladder afferent nerve activity • Increase production of intracellular cGMP = Smooth muscle relaxation • Inactivated by PDE’s • Role for PDE-inhibitors?

12. Afferent Neuropeptides Substance P Neurokinin A Calcitonin gene- related peptide (CGRP) Vasoactive Intestinal polypeptide (VIP) Pituitary adenylate cyclase-activating peptide (PACAP) Enkephalins • Contained in capsaicin-sensitive, C-Fiber bladder afferents • Released in bladder by noxious stimulation • Inflammatory response  plasma extrav., vasodilation, and alter bladder smooth muscle activity • transmitters at afferent terminals of the spinal cord • Receptors of Tachykinins • NK1R  blood vessels to induce plasma extrav. • NK2R  bladder contractions • NK2R  increase excitability during bladder filling or inflammation

14. Prostanoids • Prostaglandins, Thromboxane • Manufactured throughout the lower urinary tract • Bladder Mucosa Contains: • PGI2, PGE2, PGE2a, Thromboxane A • PGF2, PGE, PGE2 = Contraction • Mediated by specific receptors on cell membranes • DP, EP, FP, IP, and TP • Slow onset of action • Modulatory role • Affect neural release of transmitters or inhibit acetylcholinesterase activity

15. Endothelins • 21 amino acid peptides produced in endothelial cells • ET-1 (ET-2, ET-3) • Control of bladder smooth muscle tone • Regulation of local blood flow • Bladder wall remodeling in pathological conditions • involved in detrusor hyperplasia and overactivity seen in pts with BOO resulting from BPH • Receptors: ETA , ETB • Also have a role in nociceptive mech. in peripheral and Central Nervous System • Peripheral = induce detrusor activity • Spinal Cord = inhibit micturition through Opioid’s

16. Parathyroid Hormone Related Peptide • Manufactured by bladder smooth muscle • Detrusor relaxation

17. Sex Steroids • Do not directly affect bladder contractility, but modulate receptors and influence growth of bladder tissues • Estrogen: Effect on urinary continence in females probably reflects multiple actions on adrenergic receptors, vasculature, and urethral morphology • Increasing adrenergic receptors • NOS • Progesterone: increases electrical and cholinergic contractions of bladder

18. Transducer function of Urothelium • Urothelial cells display properties of nociceptors and mechanoreceptors • Release NO, ATP, Acetylcholine, Substance P, Prostaglandins • local chemical/mechanical stimuli  chemical signals to bladder afferents CNS

19. Serotonin (5-HT) • Neuroendocrine cells along urethra and prostate • Contraction in concentration dependent manner

20. C-Fiber Pharmacotherapy • Unmyelinated C-fibers are normally silent • Activated by noxious stimuli • Irritated state they become responsive to low pressure bladder distention • Capsaicin and Resiniferatoxin (RTX) • Vanilloids that stimulate and desensitize C fibers to produce pain and release neuropeptides • TRPV1 (transient receptor potential) • Spinal cord, DRG, bladder, Urethra, Colon • Activated  calcium/Na influx  afferent terminals  CNS • Capsaicin selectively excites and subsequently desensitizes C-fibers • RTX causes desensitization without prior excitation

21. Normal Conditions

22. Pathologic Conditions

23. Botulinum Toxin • Inhibit acetylcholine release at the presynaptic cholinergic nerve terminal = Inhibiting striated and smooth muscle contractions • Also shown to inhibit afferent nerve activity • 4 steps required for Paralysis • Toxin heavy chain  Nerve terminal receptor(?) • Internalization of toxin into nerve terminal • Translocation of light chain into the cytosol • Inhibition of neurotransmitter release • Urological uses (BTX-A) • Spinal cord injury suffering from detrusor-external sphincter dyssynergia and detrusor overactivity • Pelvic floor spasticity • BPH

24. Actions of Drugs on Smooth Muscle • Calcium Channel Blockers • Potassium Channel Openers • TCA

25. Calcium Channel Blockers • Diltiazem, Verapamil • Spontaneous and evoked contractileproperties are mediated by membrane depol. And movement of calcium into the smooth muscle cell through L-type Ca channels • Less effective in suppressing nerve-mediated contractions • Dependent on both Extracellular Ca and Intracellular Calcium • Develop a selective Ca channel blocking agent to eliminate spontaneous contractions without effecting micturition contractions?

26. K channel Openers • Cromakalim, Pinacidil • Move K+ out of cell  membrane hyperpolarization = reduction in spontaneous contractile activity • 3 K channels identified • Katp, SKCa, BKCa • Intravesicular instillation of bladder selective Katp = reduced detrusor activity in rats with BOO

27. TCA • Imipramine, Amitriptyline • Antimuscarinic activity • Inhibition of Ca translocation • Direct smooth muscle relaxant

28. Spinal Ascending/Descending Paths • Glutamatergic • Inhibitory Amino Acids • Adrenergic • Serotonergic • Opioid • Purinergic

29. Glutamatergic • Glutamate • Bladder Contraction • Excitatory transmitter in afferent limb of micturation reflex • Suppressed by NMDA receptor antagonists

30. Inhibitory Amino Acids • Intrathecal injection of GABAa or GABAb agonists increases bladder capacity and decreases voiding pressures (rats) • Baclofen • Glycine levels low in rats with chronic spinal cord injuries • Increasing dietary stores of glycine can restore bladder function

31. Adrenergic •  adrenoceptors can mediate excitatory and inhibitory influences on the lower urinary tract • Efferent and Afferent limbs of the Micturition reflex receive excitatory and inhibitory input, respectively from spinal noradrenergic systems

32. Serotonergic • Raphe nucleus of the caudal brainstem autonomic and sphincter motor nuclei in the lumbosacral spinal cord • Inhibitory • Duloxetine • Combined Norepinephrine/5 HT reuptake inhibitor • Increase neural activity to external urethral sphincter and decreases bladder activity through the CNS

33. Opioids • Inhibitory action of reflex pathways in the spinal cord

34. Purinergic • Adenosine A1 • Inhibitory action

35. PMC and Supraspinal Mech.

36. Glutamate • Excitatory in Micturition pathway

37. Cholinergic • Excitatory/Inhibitory • M1R and Protein Kinase C

38. GABA • Inhibitory • Acts on GABAa/GABAb Receptors

39. Dopaminergic • Inhibitory Reflex • D1 • D5 • Substantia nigra • Facilitatory • D2 • D3 • D4

40. Opioids • Inhibitory •  and δ Receptors

41. Mechanisms of Detrusor Overactivity

42. Spinal Cord Injury/Neurogenic Detrusor Overactivity • Damage above the Sacral level = detrusor overactivity • reorganization of synaptic connections in spinal cord • Alteration of bladder afferents • Nml Micturition by lightly myelinated Aδ afferents • Post injury • Capsaicin-sensitive C- fiber mediated spinal reflex = Detrusor overactivity • UMN: MS, PD • NGF (nerve growth factor) : Implicated as Chemical mediator of disease-induced changes • NGF Antibodies?

43. Bladder Outlet Obstruction • Changes: • Detrusor hypertrophy • No change of myofilaments • Axonal degeneration • Decrease in percentage volume of Mitochondria • Increase in sarcoplasmic reticulum • Gap junctions are absent • Enlarged density of afferent and efferent nerve fibers • Unstable Contraction • Obstruction-Induced detrusor overactivity with irritative voiding symptoms has been attributed to denervation supersensitivity. • CNS alterations • New spinal circuits • NGF • Increase precedes enlargement of bladder neurons and development of urinary frequency

45. Aging • Contractility • α – adrenergic stimulation increase and decrease in β – adrenergic inhibitory responses? • Innervation and development of Gap Junctions? • Low energy production?

46. Future • Pharmacogenetics • Tissue Engineering • Gene Therapy