Yamanishi T, Yasuda K, Tojo M, Hattori T, Sakakibara R, Shimazaki J
Department of Urology, School of Medicine, Chiba University, Japan.
J Urol. 1994 Apr;151(4):1066-9. doi: 10.1016/s0022-5347(17)35184-4.
The effects of beta 2-stimulants [clenbuterol (CB) and terbutaline (TB)] on the contractility of the urethral sphincter of female dogs were studied by measuring intraurethral pressure (IUP) during stimulation of bilateral pudendal nerves. In nine dogs 1, 10 and 100 micrograms/kg. of CB were administered, but no changes in IUP were observed. In the other 33 dogs, sphincteric fatigue was experimentally prepared by electrically stimulating the pudendal nerves at 15 V, 20 Hz for 30 to 40 minutes. In fatigued sphincters, CB (n = 17) and TB (n = 7) increased the contracting pressure (pressure difference between stimulation-generated peak level and baseline level of IUP). The inotropic effect of beta 2-stimulant (TB) on the fatigued urethral sphincter was abolished by a beta-blocker, propranolol. From the present study it was concluded that beta 2-stimulants have little effect on the total contractility of the nonfatigued urethral sphincter because it is composed of smooth and striated muscles (fast- and slow-contracting muscles). However, beta 2-stimulants enhanced the contractility of fatigued urethral sphincter. These results suggest that beta 2-stimulants act on fast-contracting fibers in the urethral sphincter because the inotropic effect of sympathomimetic amine is much greater on fatigued, fast-contracting fibers than on nonfatigued ones and its depressive effect on slow-contracting fibers is not potentiated after fatigue.
通过在刺激双侧阴部神经期间测量尿道内压（IUP），研究了β2激动剂（克仑特罗（CB）和特布他林（TB））对雌性犬尿道括约肌收缩性的影响。在9只犬中，给予1、10和100微克/千克的CB，但未观察到IUP有变化。在另外33只犬中，通过以15伏、20赫兹电刺激阴部神经30至40分钟来实验性制备括约肌疲劳。在疲劳的括约肌中，CB（n = 17）和TB（n = 7）增加了收缩压（刺激产生的IUP峰值水平与基线水平之间的压差）。β受体阻滞剂普萘洛尔消除了β2激动剂（TB）对疲劳尿道括约肌的正性肌力作用。从本研究得出的结论是，β2激动剂对未疲劳的尿道括约肌的总收缩性影响很小，因为它由平滑肌和横纹肌（快收缩和慢收缩肌）组成。然而，β2激动剂增强了疲劳尿道括约肌的收缩性。这些结果表明，β2激动剂作用于尿道括约肌中的快收缩纤维，因为拟交感神经胺对疲劳的快收缩纤维的正性肌力作用比对未疲劳的纤维大得多，并且其对慢收缩纤维的抑制作用在疲劳后不会增强。
