| Objective: To study the physiologic mechanism of urinary bladder function change in the aging rats.Materials and Methods: Female Wistar rats were divided into aging group (24 month-old) and young adult group (6 month-old). In vivo, filling cystometry was performed to measure the incidence of detrusor instability, bladder compliance and volume-pressure relationship in all rats of the two groups. In vitro, the tissue bath technique was used to do experiments as follows: ①The spontaneous contraction frequency was measured in each detrusor strip; ②Tension was recorded when the detrusor strips were stretched gradually and sent back gradually; ③The tension of each detrusor strip was recorded at different lengths with electrical field stimulation-induced contractions; ④The contractile response of detrusor strips to carbochol, ATP and noradrenlin was compared in a series concentration, respectively; ⑤The relaxation response to atropine and isoprenaline was compared in a series concentration, respectively. ⑥With light microscopy and transmission electron microscopy, the detrusor pathologic modification were compared between the two groups.Results: Cystometry findings: The incidence of DI in aging group is increased compared with young adult group; There is a significantly increased maximum volume in the aging rats' bladder, no significant difference was found in leak point pressure between the two groups. Detrusor strip experimentals findings: ①In a certain preload, the spontaneous contraction was appearance in all the two groups, but the frequency in the aging group is significantly higher that that of young adult group; ②When detrusor strip stretched gradually, the tension of which increased more slowly in aging group than contrast group; Contrarily, when the strip relaxed from its increased length, the tension decreased faster in aging group than in contrast group. ③The same changes were also found in various length of detrusor strips evoked by electron field stimulation. More interesting, the active tension, which EFS made, has no significant difference in the two groups. ④The contraction elicited by ATP increased significantly in aging detrusor strips compared to the contrast; It was also increased significantly in aging strips that isoprenaline relaxes the tension induced by EFS.⑤There was no modification of contractility in aging strips thatinduced by carbochol and noradrenalin, as well as the contractility inhibition by atropine. Pathologic findings: ①Compared to that of young adult rats, the gap beteen detrusor smooth muscle cells of aging rats grew more widely, and detrusor fascicles arrange became disorderly; ②the ratio of smooth muscle decreased significantly as well as the ratio of collagen increase significantly in aging detruor as compared with the young adult detrusor. ③Ultrastructurlly, there was "dense-band" structure in aging bladder smooth muscle membrane, the protrusion junction between detrusor smooth muscle cells of aging group increased, myofilament got sparse and disorder, and mitochondria degenerated.Conclusions: ①Excitability of aging detrusor increased; ②Compliance increased combined with elasticity decreased in aging strips; ③The active contraction had no changes with age; ④Sensitivity increased of purinergic and β-adrenergic receptor, and no changes was found with other receptor. In a word, modifications of myogenic factor together with some neurogenic factor maybe play important roles in etiology of aging bladder dysfunction. |
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