García-Pascual A, Triguero D
Department of Physiology, Faculty of Veterinary Sciences, Complutense University, Madrid, Spain.
J Physiol. 1994 Apr 15;476(2):333-47. doi: 10.1113/jphysiol.1994.sp020135.
Isolated transverse and longitudinally oriented preparations of sheep urethra precontracted with noradrenaline responded to electrical field stimulation (EFS) with stimulus-dependent non-adrenergic, non-cholinergic (NANC) relaxations. Exogenous nitric oxide (NO) (acidified NaNO2), S-nitroso-L-cysteine (NC), sodium nitroprusside (SNP), 8-Br-cGMP, dibutyryl-cAMP, forskolin and isoprenaline each relaxed precontracted transverse urethral preparations in a concentration-dependent manner in order of protency: NC > forskolin > isoprenaline = SNP > NO > 8-Br-cGMP = dibutyryl-cAMP. Longitudinally oriented preparations responded to NO and NC with concentration-dependent relaxation, no different from that observed in transverse strips. Methylene blue (MB) and oxyhaemoglobin (HbO2) each shifted the concentration-response curve for NO to the right without affecting EFS-induced relaxation. Similarly, concentration-dependent responses to NC were not affected by MB. The inhibition of relaxation to NO by MB was prevented by superoxide dismutase, suggesting the inhibition was caused by extracellular generation of superoxide anions. EFS-induced relaxation was accompanied by elevation of cGMP. However, for the same level of relaxation, exogenous NO and NC induced 15- and 23-times higher increases in cGMP values, respectively, than EFS. cAMP levels were not affected by EFS- or NO-induced relaxation, although a large increase accompanied relaxation induced by forskolin. Forskolin also increased cGMP content. Pretreatment with MB reduced basal levels of cGMP and inhibited both relaxation and rise in cGMP levels induced by NO. SNP-elicited relaxant responses, in the presence of MB, were accompanied by an accumulation of cGMP; cAMP levels were unaffected. MB reduced cGMP levels induced by NC, while the relaxant response was unchanged. In urethral preparations prelabelled with [3H]myoinositol, exposure to NA caused an accumulation of [3H]inositol phosphates, which was unaffected by pretreatment with 8-Br-cGMP or dibutyryl-cAMP. EFS failed to induce a relaxant response in excess [K+]o-contracted preparations, while relaxation with exogenous NO was unaffected. Ouabain abolished EFS-induced relaxation and reduced responses to NO. Neither TEA nor glibenclamide affected relaxation to either EFS or NO. Relaxation elicited by SNP was not accompanied by any change in cGMP or cAMP levels, and was unaffected by MB, HbO2, K+ channel blockers (TEA and glibenclamide), ouabain or high [K+]o solution. This suggested that relaxation was caused by a mechanism independent of NO generation. A dense network of NADPH diaphorase-positive fibres associated with both the circular and longitudinal smooth muscle layers of sheep urethra was found.(ABSTRACT TRUNCATED AT 400 WORDS)
用去甲肾上腺素预收缩的绵羊尿道的离体横向和纵向取向标本，对电场刺激（EFS）产生刺激依赖性非肾上腺素能、非胆碱能（NANC）舒张反应。外源性一氧化氮（NO）（酸化的亚硝酸钠）、S-亚硝基-L-半胱氨酸（NC）、硝普钠（SNP）、8-溴-cGMP、二丁酰-cAMP、福斯可林和异丙肾上腺素，均以浓度依赖性方式使预收缩的横向尿道标本舒张，效力顺序为：NC＞福斯可林＞异丙肾上腺素 = SNP＞NO＞8-溴-cGMP = 二丁酰-cAMP。纵向取向标本对NO和NC产生浓度依赖性舒张反应，与在横向条带中观察到的无差异。亚甲蓝（MB）和氧合血红蛋白（HbO2）均使NO的浓度-反应曲线右移，而不影响EFS诱导的舒张。同样，MB不影响对NC的浓度依赖性反应。超氧化物歧化酶可防止MB对NO舒张的抑制，提示该抑制是由细胞外超氧阴离子生成所致。EFS诱导的舒张伴有cGMP升高。然而，对于相同程度的舒张，外源性NO和NC分别使cGMP值升高的幅度比EFS高15倍和23倍。EFS或NO诱导的舒张不影响cAMP水平，尽管福斯可林诱导的舒张伴有cAMP大幅升高。福斯可林也增加cGMP含量。用MB预处理可降低cGMP基础水平，并抑制NO诱导的舒张及cGMP水平升高。在存在MB的情况下，SNP引发的舒张反应伴有cGMP蓄积；cAMP水平未受影响。MB降低NC诱导的cGMP水平，而舒张反应不变。在用[3H]肌醇预标记的尿道标本中，暴露于去甲肾上腺素导致[3H]肌醇磷酸蓄积，8-溴-cGMP或二丁酰-cAMP预处理对此无影响。EFS在高[K+]o收缩的标本中未能诱导舒张反应，而外源性NO诱导的舒张不受影响。哇巴因消除EFS诱导的舒张，并降低对NO的反应。TEA和格列本脲均不影响对EFS或NO的舒张。SNP引发的舒张不伴有cGMP或cAMP水平变化，且不受MB、HbO2、钾通道阻滞剂（TEA和格列本脲）、哇巴因或高[K+]o溶液影响。这提示舒张是由与NO生成无关的机制引起的。在绵羊尿道的环形和纵向平滑肌层中均发现了密集的NADPH黄递酶阳性纤维网络。（摘要截短于400字）
