Urethral sphincter

Two types of urinary tract symptoms are commonly seen in MS incomplete bladder emptying and incontinence. Incomplete bladder emptying is due to dyscoordination of the external urethral sphincter and detrusor activity.14 Most patients who develop this condition require intermittent or permanent uri-I nary catheterization.14 Incontinence in most MS patients is... 

The urethral sphincter, a combination of smooth and striated muscles within and external to the urethra, maintains adequate resistance to the flow of urine from the bladder until voluntary voiding is initiated. Normal bladder emptying occurs with opening of the urethra concomitant with a volitional bladder contraction. 

Duloxetine, a dual inhibitor of serotonin and norepinephrine reuptake indicated for depression and painful diabetic neuropathy, is expected to become first-line therapy for SUI. Duloxetine is thought to facilitate the bladder-to-sympathetic reflex pathway, increasing urethral and external urethral sphincter muscle tone during the storage phase. 

The effect of catecholamines on the human uterus, which can be mediated by a- and /3-adrenoceptors, depends on its functional state. During pregnancy /32-adrenoceptor stimulation decrease the uteral tonus, an effect that can be used therapeutically. /32-Adrenoceptor agonists are in use as tocolytics. In the bladder base and the urethral sphincter a-adrenoceptors are present, mediating a contraction, whereas the /32-adrenoceptors of the bladder wall induce a relaxation of the particular smooth muscles present at these structures. Ejaculation is regulated by a-adrenoceptors. 

Geriatric Considerations - Summary Compared to placebo, duloxetine is effective for the treatent of depression and painful diabetic neuropathy Few head-to-head studies are available comparing duloxetine to other agents in the treatment of depression or painful neuropathy. Because this agent may increase urethral sphincter activity, it is now being assessed as an agent for the treatment of stress urinary incontinence. This same property may increase the risk of urinary retention, although this has not been well documented. Duloxetine has not been well studied with respect to falls. 

Einally, external urethral sphincter (voluntary sphincter, or rhabdosphincter) is a striated circumscribing structure emanating from the bladder neck and bladder base detrusor through the mid-urethra in the female and intermediate prostatic urethra in the male. While also surrounding Cowper s glands in the male, these rhabdosphincter subunits contract, most likely, only with ejaculation (Hutch, 1972 Elbadawi, 1980), along with simultaneous anal rhabdosphincter, bulbo-cavernosus muscle, and cremaster muscle contractions. 

External urethral sphincter muscle probably has cholinergic and adrenergic autonomic innervation as well as cholinergic striated muscle innervation (Elbadawi and Schenk, 1974). This rhabdosphincter is unique when compared to other striated muscle in that it has a higher density of neural end-plates as well as blood vessel-independent neural plexuses. Efferent rhabdosphincter innervation is probably via the pudendal nerve while the lissosphincter efferents probably emanate from the pelvic plexus (Elbadawi and Schenk, 1974). 

Elbadawi, A. and Schenk, E.A. (1974) A new theory of the innervation of bladder musculature. 4. Innervation of the vesicourethral junction and external urethral sphincter./ Urol 111 613-615. 

In genitourinary organs, the bladder base, urethral sphincter, and prostate contain a receptors that mediate contraction and therefore promote urinary continence. The specific subtype of 04 receptor involved in mediating constriction of the bladder base and prostate is uncertain, but cxia receptors probably play an important role. This effect explains why urinary retention is a potential adverse effect of administration of the 04 agonist midodrine. 

Burnett, A.L., Calvin, D.C., Chamness, S.L., Liu, J.X., Nelson, R.J., Klein, S.L., Dawson, V.L., Dawson, T.M., Snyder, S.H. Urinary bladder-urethral sphincter dysfunction in mice with targeted disruption of neuronal nitric oxide synthase models idiopathic voiding disorders in humans, Nat. Med. 1997, 3, 571-574. 

The human uterus contains and B2 receptors. The fact that the Breceptors mediate relaxation may be clinically useful in pregnancy (see Clinical Pharmacology). The bladder base, urethral sphincter, and prostate contain receptors that mediate contraction and therefore promote urinary continence. The specific subtype of ai receptor involved in mediating constriction of the bladder base and prostate is uncertain, but uia receptors probably play an important role. The B2 receptors of the bladder wall mediate relaxation. Ejaculation depends upon normal a-receptor (and possibly purinergic receptor) activation in the ductus deferens, seminal vesicles, and prostate. The detumescence of erectile tissue that normally follows ejaculation is also brought about by norepinephrine (and possibly neuropeptide Y) released from sympathetic nerves. Alpha activation appears to have a similar detumescent effect on erectile tissue in female animals. 

Conte et al. (1991) proposed a method for simultaneous recording of vesical and the external urethral sphincter pressure in urethane-anesthetized rats. 

Studies on the Urinary Bladder and Internal Urethral Sphincter... 

In some studies, denervation of the external urethral sphincter was performed (Somma et al. 1989 Parlani et al. 1992). Rats were anesthetized with 30 mg/kg penthotal i.p., then the major pelvic ganglia, known to provide both sympathetic and parasympathetic innervation to the urinary bladder and the external urethral sphincter (Hulsebosh and Goggeshall 1982 Purinton et al. 1973 Watanabe and Yamamoto 1979) are isolated and bilaterally removed through a small incision of the lower abdomen. 

In the same preparations, somatic denervation of the external urethral sphincter was obtained by cutting the pudendal nerves. The paravertebral muscles were care-... 

Parlani M, Manzini S, Argentino-Storino A, Conte B (1992) The rat external urethral sphincter. An in vitro model to evaluate the activity of drugs on the smooth and striated components of the urinary bladder outlet. J Pharmacol Toxicol Meth 28 85-90... 

Urethral underactivity is known as stress Ul (SUl) and occurs during activities such as exercise, lifting, coughing, and sneezing. The urethral sphincter no longer resists the flow of urine from the bladder during... 

Urethral sphincter dysfunction which is due to various causes including weakness of the muscles and ligaments around the bladder neck, descent of the urethrovesical junction and periurethral fibrosis the result is stress incontinence. 

The use of a adrenoceptor blockers (e.g. phenoxy-benzamine 0.7mg/kg orally four times a day, ace-promazine 0.02-0.04 mg/kg i.m. or orally four times a day) in combination with bethanechol decreases urethral sphincter tone in horses with bladder paresis (Schott 1998). In theory, partial relaxation of the urethral sphincter could improve bladder emptying at lower intravesicular... 

Administration of estradiol cypionate (4-10 fig/kg i.m. daily for 3 days then every other day) or estradiol benzoate (10-12 xg/kg using a similar dosing schedule) has been reported to improve urinary incontinence in mares (Watson et al 1997). Estrogen receptors are present in the bladder neck and the hormone appears to modulate the effects of norepinephrine on the a adrenoceptors in the urethral sphincter, thereby improving urethral sphincter tone. However, the doses of... 

There is one report of the use of the tricyclic antidepressant imipramine hydrochloride to control urospermia in a stallion with detrusor dysfunction and decreased urethral sphincter tone (Oristaglio Turner et al 1995 see Ch. 11). Imipramine is a phe-nothiazine analog and appears to have a adrenergic effects via the blockade of norepinephrine reuptake at nerve terminals. It was administered orally at 0.8 mg/kg to this stallion 2-3 h prior to semen collection and was thought to improve urethral sphincter tone and limit urospermia. However, this improvement was not documented using urethral pressure profilometry and the owner of the stallion was also instructed to collect from the stallion shortly after it was observed to urinate. Consequently, it is not clear whether the imipramine treatment was really of any benefit. 

The lower urinary tract consists of the bladder, urethra, urinary or urethral sphincter, and the surrounding musculofascial structures including connective tissue, nerves, and blood vessels. The urinary bladder is a hollow organ composed of smooth muscle and connective tissue located deep in the bony pelvis in men and women. The urethra is a hollow tube that acts as a conduit for urine flow out of the bladder. The interior surface of both the bladder and urethra is lined by an epithelial cell layer termed transitional epithelium, which is in constant contact with urine. Previously considered inert and inactive, transitional epithelium may actually play an active role in the pathophysiology of many lower urinary tract disorders, including interstitial cystitis and UI. The urinary or urethral sphincter is a combination of smooth and striated muscle within and surrounding the most proximal portion of the urethra adjacent to the bladder in both men and women. This is a functional but not anatomic sphincter that includes a portion of the bladder neck or outlet as well as the proximal urethra. 

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