Pharmacologic perspective on the physiology of the lower urinary tract.
Myogenic activity, distention of the detrusor, and signals from the urothelium may initiate voiding. In the bladder, afferent nerves have been identified not only in the detrusor, but also suburothelially, where they form a plexus that lies immediately beneath the epithelial lining. Extracellular adenosine triphosphate (ATP) has been found to mediate excitation of small-diameter sensory neurons via P2X3 receptors, and it has been shown that bladder distention causes release of ATP from the urothelium. In turn, ATP can activate P2X3 receptors on suburothelial afferent nerve terminals to evoke a neural discharge. However, most probably, not only ATP but also a cascade of inhibitory and stimulatory transmitters and mediators are involved in the transduction mechanisms underlying the activation of afferent fibers during bladder filling. These mechanisms may be targets for future drugs. The central nervous control of micturition involves many transmitter systems, which may be suitable targets for pharmacologic intervention. gamma-Aminobutyric acid, dopamine, enkephalin, serotonin, and noradrenaline receptors and mechanisms are known to influence micturition, and potentially, drugs that affect these systems could be developed for clinical use. However, a selective action on the lower urinary tract may be difficult to obtain. Most drugs currently used for treatment of detrusor overactivity have a peripheral site of action, mainly the efferent (cholinergic) neurotransmission and/or the detrusor muscle itself. In the normal bladder, muscarinic receptor stimulation produces the main part of detrusor contraction, but evidence is accumulating that in disease states, such as neurogenic bladders, outflow obstruction, idiopathic detrusor instability, and interstitial cystitis, as well as in the aging bladder, a noncholinergic activation via purinergic receptors may occur. If this component of activation is responsible not only for part of the bladder contractions, but also for the symptoms of the overactive bladder, it should be considered an important target for therapeutic interventions.
Andersson
Karl-Erik
KE
Department of Clinical Pharmacology, Lund University Hospital, Lund, Sweden. karl-erik.andersson@klinfarm.lu.se
Hedlund
Petter
P
D000818:Animals; D002211:Capsaicin / Q000494:pharmacology / Q000627:therapeutic use; D002415:Cats; D004224:Diterpenes / Q000494:pharmacology / Q000627:therapeutic use; D006801:Humans; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D051381:Rats; D011983:Receptors, Purinergic / Q000187:drug effects / Q000502:physiology; D015320:Tachykinins / Q000494:pharmacology / Q000627:therapeutic use; D001743:Urinary Bladder / Q000187:drug effects / Q000294:innervation / Q000503:physiopathology; D001745:Urinary Bladder Diseases / Q000188:drug therapy / Q000503:physiopathology; D014551:Urinary Tract / Q000187:drug effects* / Q000503:physiopathology; D014553:Urinary Tract Physiological Phenomena / Q000187:drug effects*; D014554:Urination / Q000502:physiology; D014555:Urination Disorders / Q000188:drug therapy* / Q000503:physiopathology; D019459:Urothelium / Q000187:drug effects / Q000502:physiology
D004224:Diterpenes; D011983:Receptors, Purinergic; D015320:Tachykinins; C024353:resiniferatoxin; D002211:Capsaicin