Biomechanical characterization of the urethral musculature

Abstract

Rigorous study of the associations between urethral structural anatomy and biomechanical function is necessary to advance the understanding of the development, progression, and treatment of urethral pathologies. An ex vivo model was utilized to define the relative biomechanical contributions of the active (muscle) elements of the female urethra relative to its passive (noncontractile) elements. Whole urethras from female, adult rats were tested under a range of applied intraluminal pressures (0 to 20 mmHg) as a laser micrometer simultaneously measured midurethral outer diameter. Active tissue characterization was performed during induced contraction of either smooth muscle alone (N(omega)-nitro-l-arginine, phenylephrine), striated muscle alone (sodium nitroprusside, atropine, hexamethonium, acetylcholine), or during collective activation of both muscles (N(omega)-nitro-l-arginine, phenylephrine, acetylcholine). The subsequent collection of paired passive biomechanical responses permitted the determination of parameters related to intrinsic muscle contractile function. Activation of each muscle layer significantly influenced the biomechanical responses of the tissue. Measures of muscle responsiveness over a wide range of sustained opposing pressures indicated that an activated striated muscle component was approximately one-third as effective as activated smooth muscle in resisting tissue deformation. The maximum circumferential stress generated by the striated muscle component under these conditions was also determined to be approximately one-third of that generated by the smooth muscle (748 +/- 379 vs. 2,229 +/- 409 N/m(2)). The experiments quantitatively reveal the relative influence of the intrinsic urethral smooth and striated muscle layers with regard to their effect on the mechanical properties and maximum functional responses of the urethra to applied intralumenal stresses in the complete absence of extrinsic influences.

Ex vivo biomechanical, functional, and immunohistochemical alterations of adrenergic responses in the female urethra in a rat model of birth trauma

“…In the present study, urethras were assessed functionally (under constant static pressure of 8 mmHg) and biomechanically (under increasing pressure from 0 to 20 mmHg) in the presence of a concentration of an ␣ 1 -adrenergic receptor agonist, which produces a maximum contraction of urethral smooth muscle (12,14). The proximal urethral contractile response to PE increased in VD preparations (Table 1).…”

“…PE was added to contract urethral smooth muscle via ␣ adrenergic receptors; representative tracing for control (top) and vaginal distension (VD; bottom) proximal segments is shown. Average %OD response values are summarized in Table 1. thickness, as described previously (14,30). If the urethral specimens are assumed to be thick-walled, linearly elastic, isotropic cylinders, the circumferential stress ( ) at any point r through the thickness of the wall may be estimated by:…”

Involvement of reflex urethral closure mechanisms in urethral resistance under momentary stress condition induced by electrical stimulation of rat abdomen

“…On the other hand, the reflex urethral contractions, which are induced by passive elevation of P ves for 2 min by changing the height of the saline reservoir connected to the bladder catheter, are partially reduced by the bilateral transection of the somatic nerves or the hypogastric nerves, indicating that both the striated and smooth muscle components are involved in the urethral closing. Furthermore, the study of rat urethral functions using an ex vivo system for investigating the biomechanical properties shows that the smooth muscle component rather than the striated muscle component in the isolated urethra greatly contributes to the resistance to intraluminal pressure elevation (11,12), although it is also known that the smooth muscle is not suitable to show the quick responses. Together, these findings indicate that it is highly conceivable that the contribution of urethral smooth muscle functions may be higher under the basal condition without stress or under stress conditions lasting for a long time.…”

Nitrergic relaxations and phenylephrine contractions are not compromised in isolated urethra in a rat model of diabetes

“…Adrenergic effects on EUS and their involvement in micturition reflexes are thought to be mediated by spinal or supraspinal alpha adrenergic receptors (reviews: (Andersson and Wein, 2004;Canda et al, 2008;de Groat and Yoshimura, 2001)). Consequently phenylephrine was used as a smooth muscle specific stimulator in previous studies (Jankowski et al, 2004(Jankowski et al, , 2006Prantil et al, 2007). Thus, it is likely that in our experiments, PE effects on muscle tone are mainly mediated by adrenergic receptors in the smooth muscle.…”

“…Thus, it is likely that in our experiments, PE effects on muscle tone are mainly mediated by adrenergic receptors in the smooth muscle. Second, striated muscle does not seem to have a basal tone (in the absence of electrical stimulation), as opposed to the smooth muscle which maintains a tone in in vitro preparations (Jankowski et al, 2006). Therefore effects of PE on basal tone are likely mediated by the smooth muscle.…”