The present study compared the contractile and relaxant responses of male and female rabbit bladder neck and urethra to field stimulation (FS) and various contractile and relaxant agents, with special attention paid to the involvement of nitric oxide (NO) in the mediation of field-stimulated relaxation. FS at basal tension elicited a frequency-dependent contractile response in all preparations. The maximal response to high frequency FS was significantly greater in the bladder neck strips isolated from male rabbits than in those from female rabbits. There were no significant differences in the response to bethanechol or phenylephrine between strips isolated from males and females. Field-stimulated responses of the strips from male bladder neck and urethra were greater than the response to phenylephrine. The responses of all strips to FS were greater than those to bethanechol. In addition, the response to phenylephrine was generally greatere than that to bethanechol. Phentolamine was a significantly more effective inhibitor of the response of the female bladder neck and urethral strips to FS than of the response of the male strips. The contractile response of all strips to phenylephrine was generally greater than that to bethanechol for both sexes and for both bladder neck and urethral strips. NG-nitro-L-arginine methylester (L·NAME) inhibited totally the field-stimulated relaxation of all strips. Isoproterenol stimulated a slowly developing but significant inhibition of phenylephrine prestimulated contractions. In conclusion, significant differences exist in the magnitude of field-stimulated relaxation between the bladder neck and urethra of both male and female rabbits, and, for all tissues, field-stimulated relaxation could be completely inhibited by pretreatment with L·NAME, an NO synthesis inhibitor.
Our results suggest that women with preoperative low Qmax experienced no definite unfavorable voiding problem from the MUS procedure compared to those with normal voiding function. MUS procedure may be regarded as a safe and successful procedure in SUI women with low Qmax.
This initial study correlates the passive length-tension relationship, contractile and relaxant responses to field stimulation and contractile responses to specific autonomic agonists and antagonists with gestational age. Fetal bovine bladders were separated into three groups based on the head-rump length (FL): 30 to 45 cm. (early gestation), 50 to 65 cm. (middle gestation) and 70 to 85 cm. (late gestation). Each bladder was separated into upper and lower bladder segments; longitudinal strips of smooth muscle were isolated and placed in individual muscle baths. Passive length-tension studies demonstrated that compliance was greatest in the bladder of late gestation and lowest in the bladder of early gestation period. Field stimulation (FS) elicited frequency-dependent contractile responses in all strips. In the upper bladder, the maximal response and maximal rate of tension generation to FS was lowest in the youngest fetuses and increased in proportion to the gestational age. In the lower bladders, there were no gestational age-related differences in the maximal response or maximal rate of tension generation in response to field stimulation. The maximal response of the upper bladder to bethanechol increased significantly from the youngest gestational age to mid-gestation, with no further changes between mid- and late gestation. The maximal response to field stimulation and bethanechol were equal between upper and lower bladder segments for the youngest gestational bladders, whereas for the oldest gestational ages, the maximal response of the upper bladder to FS and bethanechol were significantly greater than the responses of the lower bladder. In the presence of maximal precontraction with bethanechol, FS induced a rapid and marked decrease in tension. The magnitude of the relaxation was substantially greater for the strips of lower bladder than for the strips of upper bladder at late gestation. In lower bladders, the magnitude of the field stimulated relaxation was greater in the strips from the older fetuses than in the strips from younger fetuses. In all strips, field stimulated relaxations were completely inhibited by pretreatment with L-NAME (an inhibitor of nitric oxide synthesis), indicating that the FS-induced relaxation was due to nitric oxide. In addition to nitric oxide-induced relaxation, beta adrenergic stimulation also induced a significant relaxation of the isolated strips. In summary, these data suggest that, in the tubular shaped fetal bovine bladder, there were distinct differences in the autonomic responses between the upper bladder segment and the lower bladder segment in the late gestation period.
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