Effects of transmural field stimulation in isolated smooth muscle of human rectum and internal anal sphincter.

Smooth muscle preparations from the circular muscle layer of the most distal rectum and the proximal and distal human internal anal sphincter (IAS) mounted in organ baths to record isometric tension developed spontaneous tension. Transmural electrical field stimulation (TMS) induced frequency- and impulse duration-dependent relaxations sensitive to tetrodotoxin in the stimulation range of 0.5-40 Hz and 0.04-0.6 ms. Poststimulus contractions were most frequent and prominent in rectal preparations. Maximal relaxations were comparable in the three locations and were achieved at 10 Hz and 0.4 ms. The frequency inducing half-maximal response was lower in rectal strips compared with IAS. Phentolamine (10-(6) M) enhanced relaxations and diminished off-contractions at 40 Hz in distal IAS. N omega-nitro-L-arginine (L-NNA) concentration dependently inhibited both relaxations and off-contractions (10 Hz, 0.4 ms). The pD2 values (-log EC50) of L-NNA were lower in rectal muscle compared with those in IAS. L-Arginine (10-(4) M) inhibited the blocking effect of L-NNA. In one-half of the preparations, L-NNA reversed the relaxations to duration contractions (15-40 Hz), which were inhibited by atropine in rectal preparations and by phentolamine in IAS. In conclusion, excitatory innervation of the IAS is alpha-adrenergic and cholinergic in the rectum. A product of the L-arginine-nitric oxide pathway mediates the TMS-induced inhibition of the muscle and is also involved in poststimulus contractions.

The effect of oophorectomy on mechanical properties of rabbit cerebral and coronary isolated small arteries.

OBJECTIVE: Our purpose was to study the effect of oophorectomy on the passive and active mechanical characteristics of rabbit small cerebral and small coronary arteries. STUDY DESIGN: Ring preparations of small cerebral and small coronary arteries from rabbits that had undergone oophorectomy and sham operation were mounted on myographs 6 weeks after operation. Experiments were performed as follows. (1) concentration-response relations for vasopressin (10(-11) to 10(-7) mol/L), U46619 (10(-10) to 10(-6) mol/L), 5-hydroxytryptamine (10(-7) to 10(-5) mol/L), and endothelin (10(-13) to 10(-7) mol/L); (2) relaxing effects of acetylcholine (10(-8) to 10(-4) mol/L); (3) length-tension relations after addition of high potassium (124 mmol/L), vasopressin (10(-7) mol/L), and a mixture composed of potassium (124 mmol/L), vasopressin (10(-7) mol/L), and prostaglandin F 2 alpha (10(-5) mol/L); (4) calculation of vessel morphologic features and determination of hydroxyproline as a measure of collagen content. RESULTS: Oophorectomy did not influence basal tone, relaxant effects of acetylcholine, vessel morphologic features, elastic characteristics, or hydroxyproline content of the vessels. However, in cerebral arteries at a normalized lumen diameter, oophorectomy induced a marked increase in the force development after stimulation with agonists but not after depolarization with high potassium. The reason for this was a leftward shift in the active length-tension curves (vasopressin activation). In coronary arteries none of these changes were seen after oophorectomy. CONCLUSION: These data demonstrate that withdrawal of ovarian hormones changes the position of the active length-tension curve for pharmacomechanical but not electromechanical coupling of small cerebral arteries without interference with the elastic characteristics of these vessels.

Transmitter interactions in rabbit internal anal sphincter.

The aim of the present study was to investigate the relative importance of the different putative nonadrenergic noncholinergic (NANC) mediators and their interplay with cholinergic nerves in the rabbit internal anal sphincter (IAS). IAS preparations were mounted in organ baths for recording of isometric tension. Transmural field stimulation (TMS; 5-s trains; supramaximal voltage, 140-160 V; 0.4-ms impulse duration) was applied every 2 min with frequencies varying from 0.2 to 32 Hz. TMS induced frequency-dependent relaxations that amounted to 89.3 +/- 2.2% (n = 7). N omega-nitro-L-arginine (L-NNA; 10(-7)-10(-4) M; 8 Hz) reduced relaxations and this effect was partially inhibited by preincubation with L-arginine (10(-4) M). The effect of L-NNA was attenuated by atropine preincubation. Apamin (10(-6) M) shifted the frequency-response curve to the right but left maximal relaxations in response to TMS unaffected. In the presence of L-NNA (10(-4) M) and atropine (10(-6) M), the action (area between the frequency-response curve with or without a substance) of apamin was more pronounced, but, despite the presence of both L-NNA and apamin, some relaxation still remained. The frequency-response curve (control) was significantly shifted to the right by carbachol (10(-6) M). Concentration-response experiments showed that the response to exogenous nitric oxide (NO; 10(-7)-10(-4) M) was unaffected by carbachol (10(-6) M) preincubation, whereas responses to vasoactive intestinal polypeptide (VIP) and ATP were significantly reduced.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological identification of different inhibitory mediators involved in the innervation of the internal anal sphincter.

1. Inhibitory non-adrenergic, non-cholinergic (NANC) responses were studied in isolated strips from the rabbit internal anal sphincter. 2. In the presence of atropine and guanethidine, transmural field stimulation induced frequency-dependent relaxations that reached a plateau at frequencies > or = 4 Hz. 3. These relaxations were inhibited by apamin (10(-6) M) and by N omega-nitro-L-arginine (L-NOARG, 10(-4) M). With these two substances in combination, relaxations were still seen in response to field stimulation, but only at frequencies > 2 Hz. 4. In the presence of both apamin (10(-6) M) and L-NOARG (10(-4) M), responses at high frequencies consisted of a fast relaxation followed by a slow return to prestimulus tension level. alpha-Chrymotrypsin hastens the return of tension to prestimulus level after high frequency stimulation. 5. Zinc-protoporphyrin IX, an inhibitor of haeme oxygenase, had a significant inhibitory effect on relaxations induced by transmural field stimulation. It was found, however, that responses to sodium nitroprusside and to isoprenaline (both 10(-9)-10(-4) M) were reduced comparably, indicating that the effect of zinc-protoporphyrin IX was unspecific. 6. It is concluded that pharmacological analysis allows identification of at least three distinguishable components of the inhibitory NANC innervation of the rabbit internal anal sphincter. The study does not allow conclusions about the role of carbon monoxide, a recently proposed mediator of NANC responses in opossum internal anal sphincter.

Mechanical properties of isolated smooth muscle from human rectum and internal anal sphincter.

The passive and active length-tension relations of the circular smooth muscle layer of the human distal rectum and the proximal and distal internal anal sphincter were investigated. Muscle strips were prepared and mounted in organ baths for recording of isometric tension. Resting lengths (LR) were measured, and the preparations were elongated stepwise. At each length, the corresponding values for passive tension, spontaneous active resting tension, and the submaximal active tension were recorded. Elongations of 200-380% of LR were possible before a sharp increase in passive tension occurred. None of the mean tension values measured at length for maximal active tension (LO) differed significantly among the three muscle types. All strips developed active resting tension. This tension was myogenic and contributed 10 +/- 3, 23 +/- 6, and 27 +/- 6% to the total active performance of rectal and proximal and distal sphincter preparations, respectively. Collagen constituted approximately 50% of smooth muscle biopsies, with highest contents in distal internal anal sphincter. This study provides an acceptable method for assessing the optimal experimental length by stretching the strips in an inactive state to 200% of LR, followed by individual adjustment of the passive tension to 5 mN/mm2 measured at 200% of LR.

[The role of nitrogen oxide synthesis for relaxation of the internal anal sphincter]. / Betydningen af nitrogenoxidsyntese for relaksation af den interne anale sphincter.

The purpose of the present study was to examine the role of the L-arginine-nitric-oxide pathway in neurogenic relaxation of the internal anal sphincter. Muscle strips representing the internal anal sphincter were prepared from 17 adult opossums. The preparations were mounted in organ baths for recording of isometetric tension. N omega-nitro-L-arginine, an agent known to inhibit the L-arginine-nitric oxide pathway, concentration-dependently reduced relaxation induced by transmural field stimulation. At the highest concentration of N omega-nitro-L-arginine (10(-4) M), no relaxation was evoked at any frequency tested (0.5-40 Hz). The inhibitory response to exogenous VIP was unaffected by N omega-nitro-L-arginine pretreatment, indicating that VIP relaxation does not utilize the L-argining-nitric oxide pathway. It is concluded that the non-adrenergic, non-cholinergic innervation of the internal anal sphincter involves an inhibitory substance generated from the L-arginine--No pathway. Whether this substance is nitric oxide or a related nitroso compound remains to be settled.

Involvement of the L-arginine-nitric oxide pathway in internal anal sphincter relaxation.

The purpose of this study was to examine the role of the L-arginine-nitric oxide pathway in neurogenic relaxation of the internal anal sphincter. Muscle strips representing the internal anal sphincter were prepared from 17 adult opossums. The preparations were mounted in organ baths for recording of isometric tension. N omega-nitro-L-arginine, an agent known to inhibit the L-arginine-nitric oxide pathway, concentration-dependently reduced relaxations induced by transmural field stimulation. At the highest concentration of N omega-nitro-L-arginine (10(-4) mol/L), no relaxation was evoked at any frequency tested (0.5-40 Hz). The inhibitory response to exogenous vasoactive intestinal polypeptide was unaffected by N omega-nitro-L-arginine pretreatment, indicating that vasoactive intestinal polypeptide relaxation does not use the L-arginine-nitric oxide pathway. In addition, responses to forskolin and sodium nitroprusside were not influenced by N omega-nitro-L-arginine preincubation, suggesting that the effect observed was not caused by a direct influence on the adenylate or the guanylate cyclases. It is concluded that the nonadrenergic, noncholinergic innervation of the internal anal sphincter involves an inhibitory substance generated from the L-arginine-nitric oxide pathway. Whether this substance is nitric oxide or a related nitroso compound remains to be settled.