Involvement of Rho-kinase in the contractile mechanism of human ureteral smooth muscle

AIM: Even though many agents have been implicated as modulators of ureteral contractile activity, the exact mechanisms that control human ureteral smooth muscle contractility have yet to be clearly defined. Recently, Rho-kinase has been reported to be involved in the contractile mechanism of smooth muscles in various organs. In the present study, we sought to investigate whether or not Rho-kinase is expressed in the human ureteral smooth muscle, and to study its role regarding human ureteral smooth muscle contractility. METHODS: Ureteral samples were obtained from human adult subjects undergoing radical nephrectomy. Immunohistochemistry and Western blotting were performed to determine the presence of Rho-kinase in human ureter. Functional studies were performed with human ureteral strips suspended in organ bath, and the effects of Y-27632, a specific inhibitor of Rho-kinase, on baseline tensions, spontaneous contractions, and electrical field stimulation (EFS)-induced contractions were analyzed. RESULTS: The results of immunohistochemistry and immunoblotting study indicated that Rho-kinase is present in human ureteral smooth muscle. In functional analysis, Y-27632 was shown to decrease the baseline tension. And, both spontaneous and EFS-induced contractile responses of human ureteral strips were attenuated by Y-27632 in dose-dependent manners. CONCLUSIONS: For the first time, the results of the present study indicate that Rho-kinase is present in human ureteral smooth muscle and may play an important role in the intricate mechanism of human ureteral contractility and tone.     

Effect of extracellular calcium and calcium-blocking agents on detrusor contractility: An in vitro study

The effects of varying concentrations of calcium in the bathing solution and the effects of varying doses of the calcium-blocking agents verapamil, diltiazem, and nifedipine on baseline tension, magnitude, and frequency of spontaneous contractions and on the contractile responses to acetylcholine, bethanechol, and electrical stimulation were tested on guinea pig bladder muscle strips suspended in a muscle bath. Over a wide range of calcium concentration (10^?6 ?4.8 × 10^?3 M) no significant changes were noted in the aforementioned spontaneous and induced contractile activity. All parameters were, however, significantly depressed in a calcium-free bathing solution. At doses of 1.0 and 2.0 μg/ml bath each of the calcium-blocking agents significantly depressed the aforementioned spontaneous and induced smooth muscle contractile activity.     

Intraarterial propofol is not directly toxic to vascular endothelium.

To determine if accidental intraarterial injection of propofol results in vascular damage, the effect of bolus administration of propofol on vascular smooth muscle and the endothelium was investigated using the isolated rabbit ear artery. Ear artery segments, removed from urethane anesthetized rabbits, were perfused with Krebs solution (1 ml.min-1) and pressurized to 60 mmHg before being constricted with extraluminal norepinephrine (1.8-4.2 x 10(-6) M). The external diameter of the vessel was measured by an array of light-dependent diodes. Functional responsiveness was determined by the degree of constriction to norepinephrine and the subsequent dilatation of the artery to intraluminal acetylcholine (2 x 10(-6) M) and glyceryl trinitrate (2 x 10(-6) M), and by the myogenic reactivity to a pressure increase from 60 to 100 mmHg. These responses were measured before and after perfusion with 1% propofol for 120 s. Administration of propofol did not result in any vasoactivity nor did it increase the sensitivity to norepinephrine. Vessels maintained their capacity to dilate to both agents, while the myogenic activity was unaffected. Histologic examination of the propofol exposed vessels showed no changes to smooth muscle structure, and the endothelial layer remained intact.     

Effects of botulinum toxin A on the contractile function of dog prostate

OBJECTIVES: To study effects of botulinum toxin A (BoNT/A) on prostate contractile function in dogs. METHODS: One hundred units (N=6) or 200 units (N=5) BoNT/A was injected into dog prostate. Sham control group (N=7) received normal saline injections. Before and 1 mo after injection, prostate urethral pressure response to electrostimulation and intravenous (IV) norepinephrine was measured. Contractile responses of prostate strips were tested in tissue bath. Structural changes were evaluated with conventional histology and smoothelin immunohistochemistry. RESULTS: Injection of normal saline and 100 units BoNT/A did not significantly change prostate urethral pressure response to IV norepinephrine and electrostimulation. However, injection of 200 units BoNT/A significantly reduced prostate urethral pressure response to IV norepinephrine and electrostimulation. Contractile responses of prostate strips to potassium chloride, electrostimulation, and phenylephrine did not differ between sham control and 100U groups. In the 200U group, however, all responses were less than those of sham controls. Control and BoNT/A groups exhibited nitric oxide-related relaxation in prostate strips precontracted by phenylephrine. Injection of 100 units BoNT/A induced mild atrophy of prostate gland; injection of 200 units BoNT/A induced more pronounced atrophic changes in prostate gland and vacuoles formation in smooth muscle cells of stromal tissue. CONCLUSIONS: Injecting BoNT/A into dog prostate reduces contractile function while maintaining relaxation response of the prostate. These effects make BoNT/A a viable option in managing prostate-related symptoms. However, large, randomized clinical studies to determine long-term effects and safety of BoNT/A application in human prostates are required.     

Comparative physiology and biochemistry of rat and rabbit urinary bladder

OBJECTIVE: To compare directly the biochemistry and contractile responses of rat and rabbit bladder to different stimuli. Materials and methods Sexually mature male New Zealand White rabbits and Sprague Dawley rats were compared. Each bladder was excised while the animal was anaesthetized; longitudinal bladder strips were cut and then mounted in an organ bath. Tension (2 g) was placed on all strips and each underwent field stimulation (FS) for a total of 20 s at 1-32 Hz, 1 ms and 80 V and was exposed to carbachol (100 micromol/L), ATP (2 mmol/L) and KCl (120 mmol/L). The tension was monitored continually using a polygraph and data stored digitally in a computer. The responses to each stimulus were determined as the maximum tension generated, maximum rate of tension generation and duration to a maximum response. The Ca2+- ATPase activity of the rat and rabbit bladder was determined. Bladder pressures were then predicted from the strip data using Laplace's law and compared with published values. RESULTS: Contractile responses (per unit tissue mass) of rat bladder strips were significantly greater than those of rabbit bladder strips at all frequencies of FS and to carbachol, KCl and ATP. The rate of contractile force generated by rat bladder strips in response to all stimuli were significantly greater than that generated by rabbit strips. Rabbit bladder strips took significantly longer to generate maximum tension than did rat bladder strips in response to pharmacological stimuli. In response to FS, rat strips took significantly longer than rabbit strips to generate maximum tension. Although the predicted rat bladder pressures were significantly greater than those for rabbit, the predicted pressures for both the rat and rabbit were significantly lower than the pressure responses of the isolated whole bladder model. The contractile data correlated well with the Ca2+-ATPase activity data; rat bladder had seven times the enzyme activity of rabbit bladder. CONCLUSION: Per unit mass, rat bladder is capable of generating more than five times the tension of rabbit bladder. Similarly, the rate of tension generation by rat bladder is three to five times greater than that by rabbit bladder. The duration to maximum tension generated in response to FS compared with pharmacological stimuli was affected by the inherent difference in the rate of contractile response to electrical activation compared with agents which diffuse through tissue, and by the difference in size between rat and rabbit bladder smooth muscle cells.     

Contractile activity of mouse small intestinal longitudinal smooth muscle

BACKGROUND: Interest in genomic modulation experimentally often necessitates use of mouse models. MATERIALS AND METHODS: AIM: To characterize and quantitate smooth muscle contractile activity of the mouse small intestine using in vitro techniques. Full-thickness jejunal and ileal muscle strips from mice were cut in the direction of longitudinal muscle, suspended in tissue baths (37 degrees C), and connected to force transducers. Spontaneous contractility and two dose-response curves to the cholinergic agonist bethanechol and adrenergic agonist norepinephrine were quantitated for 6 h. RESULTS: Total contractile activity increased over 4 to 5 h in jejunum (P < 0.01) but not in ileum. Frequency of contractions (counts/min) in jejunum increased from 16 to 33 (P < 0.01) in the first 4 h, then remained stable; ileal frequency did not change. One hour of cold preservation had no major effect on contractile activity and frequency. Bethanechol increased and norepinephrine decreased contractile activity in dose-dependent fashion. The dose of bethanechol producing 50% increase in maximal response did not differ between the first and second dose-response; in contrast, the concentration of norepinephrine producing 50% decrease in activity for the second dose-response in jejunum was decreased compared to the first dose-response (P < 0.01). Cold preservation had no substantive effect on agonist responses. CONCLUSION: Experiments in murine jejunal but not ileal longitudinal muscle in vitro must consider early changes in contractile activity after tissue harvest. These experiments serve as a baseline for comparison of stimuli or genetic modifications on murine contractile activity of longitudinal muscle in vivo.     

Characteristics of spontaneous contraction and effects of isoproterenol on contractility in isolated rabbit renal pelvic smooth muscle strips

The contractile characteristics and the contractile responses to isoproterenol were examined by measurement of the isometric force in three types of smooth muscle strips obtained from the upper and lower parts of the renal pelvis and longitudinal strips encompassing the entire length of the renal pelvis. Regular rhythmic contraction was recorded from the upper renal pelvic strip with a frequency of 8.4 +/- 0.9 times per minute and from the lower renal pelvic strip with a frequency of 2.3 +/- 0.4 times per minute. The contractile frequency in the whole pelvic strip encompassing the entire longitudinal length of renal pelvis was found dependent on that in the upper renal pelvic strip. Isoproterenol caused an increase of contractile force in the upper pelvic strip and a decrease in the lower pelvic and whole pelvic strips. The results seem to suggest that the smooth muscle of the upper part of the renal pelvis is distinct from other smooth muscles and resembles heart muscle in its contractile response to isoproterenol.     

Intracellular mechanisms of halothane's effect on isolated aortic strips of the rabbit

The intracellular mechanisms of halothane action were examined in vascular smooth muscle from the aorta. Medial layers of the aorta from rabbits were mounted on photodiode tension transducers, stretched to 20 mg resting tension, and "skinned" with saponin. The skinned fiber preparations were then immersed in bathing solutions to study the effects of halothane (0.5-2%) on Ca2+ activation of the contractile proteins, and Ca2+ uptake and release from the sarcoplasmic reticulum (SR) using caffeine-induced tension transients. For comparison, isolated intact aortic rings were mounted on Blinks' dual tissue bath and attached to force transducers. The preparations were contracted with either 40 mM KCl, or norepinephrine (NE) followed by acetylcholine (ACh)- or sodium nitroprusside (SNP)-induced relaxation. At steady state contraction or relaxation, the effects of halothane (1-3%) were studied. The steady state tension during halothane was expressed as a percentage of the steady state tension before administration of halothane. In the isolated intact aortic rings, halothane (1-3%) produced biphasic effects on KCl-induced tension, i.e., an initially slight increase followed by decreases, independent of endothelium. Halothane markedly increased tension in the ACh- or SNP-relaxed state. The effects were dose-dependent. In the skinned aortic strips, halothane slightly decreased maximum Ca2+-activated tension development of the contractile proteins. Halothane decreased Ca2+ accumulation in the SR and increased Ca2+ release from the SR in a dose-dependent manner. The halothane-induced increases in Ca2+ release from the SR were blocked by ryanodine, an SR Ca2+ release channel blocker. It is concluded that halothane directly causes vascular contraction or relaxation, depending on the condition, and that halothane's effects on the SR may play a role.     

Normal detrusor is more sensitive than hypertrophied detrusor to in vitro ischemia followed by re-oxygenation

Partial outlet obstruction results in marked metabolic as well as contractile alterations. Specifically, the ratio of anaerobic to oxidative metabolism is significantly greater in hypertrophied than normal bladder smooth muscle, lactate dehydrogenase (LDH) and lactic acid production are increased, and the contractile apparatus is altered to allow for metabolically more efficient tension generation. In addition, contractile responses of hypertrophied bladder are apparently more resistant than those of normal bladder to hypoxia. In the current experiment, we studied the effects of in vitro ischemia (hypoxia + substrate deprivation) followed by an in vitro model of reperfusion (re-oxygenation + substrate replacement) on contractile responses of normal and hypertrophied urinary bladder strips. We used repetitive field stimulation (FS) during the hypoxic period as a model for hyperreflexia. The purpose of the current study was to compare the responses of normal and hypertrophied bladder smooth muscle to repetitive stimulation in the presence of in vitro ischemia followed by re-oxygenation and substrate replacement. Thirty-two rats were separated into four groups of eight each. The rats in groups 1 and 3 were subjected to partial outlet obstruction. Two weeks later, all rats were anesthetized; their bladders were isolated and cut into four strips. Each strip was mounted in an isolated bath, and after 1-hour incubation in Tyrode's solution containing glucose (in the presence of O(2)), contractile responses to FS, carbachol, and KCl were determined. After this first set of stimulations, the strips were incubated without glucose and in the presence of N(2) for 30 minutes and 1 hour (groups 1 and 2); and for 2 and 4 hours (groups 3 and 4). For groups 1 and 2, the tissues were stimulated at 5-minute intervals with FS at 32 Hz, 1-millisecond duration, 3-second trains (in vitro model of hyperreflexia). For groups 3 and 4, no stimulations were performed during the ischemic period. At the end of the ischemic period, all strips were washed and incubated for 1 hour in the presence of O(2) and with glucose. At the end of this incubation, all strips received a second set of stimulations. a) Partial outlet obstruction resulted in a significant increase in bladder weight. b) Responses to in vitro ischemia: After in vitro ischemia, contractile responses of both normal and hypertrophied tissues to FS were reduced to a significantly greater degree than were responses to carbachol and KCl. The rate of development of contractile dysfunction was significantly greater in normal bladder tissue strips than in hypertrophied bladder strips. c) Responses to repetitive stimulation: The rate of development of contractile dysfunction was significantly greater in all strips subjected to repetitive stimulation than in those not repetitively stimulated; in addition, normal bladder strips were more sensitive than hypertrophied strips to hypoxia and substrate deprivation-induced contractile dysfunction. The rate of contractile failure induced by in vitro ischemia followed by re-oxygenation and substrate replacement was significantly greater for normal bladder strips than for hypertrophied bladder strips. These results indicate that, after partial outlet obstruction, the hypertrophied tissue is more resistant than normal tissue to hypoxia and substrate deprivation.     

Endothelial-dependent vasodilation is associated with increases in the phosphorylation of a small heat shock protein (HSP20)

PURPOSE: Increases in the phosphorylation of a small heat shock protein (HSP20) are associated with cyclic nucleotide-dependent vasorelaxation. The effect of pressure and flow on vessel diameter was studied. We hypothesized that physiologic conditions that induce vasorelaxation would lead to increases in HSP20 phosphorylation. METHODS: Flow-dependent changes in vessel diameter, at different intraluminal pressures, were measured with a laser optical micrometer in intact bovine carotid arteries. Experiments were performed in the presence and absence of norepinephrine (10(-5) mol/L). Increases in the phosphorylation of HSP20 were determined with isoelectric focusing immunoblots. RESULTS: The increase in vessel diameter was most significant at low intraluminal pressures (20 mm Hg), high flow rates (200 mL/min), and in the presence of the vasoconstrictor norepinephrine (10(-5) mol/L). The addition of methylene blue (a guanylate cyclase inhibitor) completely inhibited flow-induced vasodilation. Under conditions in which maximal flow induced vasodilation occurred, there were significant increases in the phosphorylation of HSP20. CONCLUSION: Flow-dependent vasodilation in isolated perfused segments of bovine carotid arteries was maximal when the intraluminal pressures were low and when the vessels were precontracted with norepinephrine. Flow-dependent vasodilation was inhibited by methylene blue and was associated with increases in the phosphorylation of HSP20, suggesting that the vasodilation was mediated by endothelial production of nitric oxide.     

Physiological fatigue of smooth muscle contractions in rat urinary bladder

OBJECTIVE: To characterize the physiological fatigue in bladder smooth muscles that can occur within 60 s of stimulation, which is closer to the duration of normal voiding. MATERIALS AND METHODS: Longitudinal and transverse strips of rat bladder were used; the muscles were mounted in an in vitro multi-muscle chamber, and the decline in contractile tension recorded during continuous electrical stimulation at frequencies of 5-30 Hz for 60 s. The effect of muscle length on fatigue was assessed by monitoring the decline in tension during 30 Hz stimulation at rest length, and at 60% and 100% stretched lengths of the bladder strips. To assess some of the factors involved in the development of fatigue, tension responses of fatigued muscles were monitored on exposure to 80 mm potassium or 1 microm bethanechol. RESULTS: In both longitudinal and transverse bladder strips stimulated at 30 Hz, peak contractile tension declined to 50% of original after approximately 33 s, and to 30% after 60 s of stimulation. After 10 s rest, 60% of the original tension was recovered. Increasing the frequency of fatigue stimulation from 5 to 30 Hz significantly increased the extent of the decline in tension and reduced the time to a 50% decrease in tension. Stretching the bladder strips from rest length to 100% stretched length significantly reduced the extent of tension decline and increased the time to a 50% decrease in tension. Exposure of fatigued muscles to high potassium or bethanechol generated more tension than electrical stimulation. CONCLUSION: Contractile fatigue occurs in both longitudinal and transverse strips of the bladder smooth muscles within the duration of normal voiding. Increasing the frequency of stimulation from 5 to 30 Hz increased the degree and rate of fatigue. Stretching the bladder strips from rest length by 60-100% reduced the degree and rate of fatigue. Bladder fatigue may be caused by decreased depolarization of the smooth muscle membranes, reduced release of acetylcholine from presynaptic nerve terminals, or by other yet undetermined mechanisms.     

Adrenergic innervation and stimulation of canine urethra

Sympathetic nervous innervation of the canine urethra was studied using catecholamine histofluorescent staining and the in vitro muscle bath. Morphologically, adrenergic nerves were found terminating on the urethral smooth muscle. Pharmacologically, urethral strips responded like muscle strips from the bladder base to adrenergic stimulation. This evidence supports the concept that the sympathetic nervous system supplies and modulates the function of the smooth muscle of the urethra and that urethral changes noted with adrenergic stimulation are not secondary solely to stimulation of the rich periurethral vaculature nerve supply.     

Venomotor changes caused by halothane acting on the sympathetic nerves.

Experiments were performed to determine whether depression of venomotor responses with halothane results from interference with sympathetic activation or from an effect on venous smooth muscle cells. Changes in isometric tension of isolated canine saphenous-vein strips were recorded. Adrenergic activation was achieved by transmural electrical stimulation, by addition of tyramine, and by addition of morepinephrine. Halothane (0.5 to 3 per cent) did not significantly alter basal tension. It lessened the reaction of the veins to electrical stimulation but not their response to norepinephrine; it increased the response to tyramine. Since the responses to norepinephrine and tyramine were not decreased, halothane appears to act on the nerve terminal to prevent release of neurotransmitter associated with nerve-terminal depolarization. Thus, halothane causes inhibition of electrically induced venoconstriction in cutaneous veins, probably by interfering with the release of norepinephrine from nerve terminals rather than by an inhibitory effect on the smooth muscle cells.     

In vitro Effect of Amezinium on the Rabbit Urinary Bladder: Muscle Strip and Whole Bladder Evaluation

Dose-response studies for norepinephrine and amezinium were obtained for isolated muscle strips and in vitro whole bladder preparations to investigate the effect of amezinium on the bladder. Specimens (strips from the bladder base and body, and the whole bladder) were obtained from mature female rabbits. By the muscle strip study, amezinium showed a weak contractile effect (up to 40% of spontaneous contraction) on strips from the bladder base. Muscle strips from the bladder body presented no response to amezinium. In the whole bladder preparation, administration of norepinephrine showed an increase in intravesical pressure in 4 out of 7 rabbits, whereas administration of amezinium had negligible effect on intravesical pressure.Administration of amezinium showed no influence on strips from the bladder body and the whole bladder preparation. Direct contractile response in muscle strips from the bladder base by amezinium appeared to be a favourable effect considering urinary storage.     

Study of the intracellular contractile mechanism of the urinary bladder smooth muscle using skinned fiber technique

The intracellular contractile mechanism of the urinary bladder smooth muscle was studied using the saponin-treated skinned fiber in which cell membrane was chemically removed. The chemically skinned bladder muscle showed a tension development which was dependent on Ca2(+)-concentration. The minimal Ca2(+)-concentration for the tension development was 2 X 10(-7) M Ca2+. The maximal tension was induced at 10(-5) M. This maximal tension was approximately the same as the K(+)-induced tension development observed in the intact muscle. In addition, SDS-polyacrylamide gel electrophoresis showed that the contractile proteins were still preserved in the saponin-treated bladder smooth muscle. The Ca2(+)-concentration-tension response curve shifted to the left with an increase in MgATP concentration (from 3 mM to 7 mM), indicating that the sensitivity of the skinned muscle was affected by MgATP. Mg2+ above 6 mM caused a slow tension development by itself in the absence of Ca2+. Ca2(+)-induced tension development was blocked by the addition of W-7 (calmodulin antagonist). This result suggested that calmodulin (Ca2(+)-binding protein) regulates the actin-myosin interaction in the urinary bladder smooth muscle. Caffeine solution (25 mM) caused a rapid tension development in the skinned bladder smooth muscle which was loaded with Ca2(+)-concentration, however, this tension development decreased when the loaded Ca2(+)-concentration exceeded 10(-6) M. It seems from this result that "Ca-induced-Ca release mechanism" also exists in the urinary bladder smooth muscle.     

Effects of calcium and verapamil on vesicourethral smooth muscle of rabbits

Isolated smooth muscle strips from the rabbit bladder body, bladder base, and proximal urethra were contracted with ionic calcium (Ca2+) alone and with the calcium-selective ionophore A23187, acetylcholine, norepinephrine, adenosine triphosphate (ATP), and direct electrical stimulation. The effects of Ca2+ and the calcium entry blocker verapamil on spontaneous muscle activity and on contractions induced by these agonists were examined. Ca2+ -free Tyrode's solution and verapamil, 1 x 10(-7)M and above, relaxed all of the vesicourethral smooth muscle strips. In addition verapamil, 1 x 10(-8) to 1 x 10(-6) M depending on the particular stimulant employed, noncompetitively inhibited smooth muscle contractions elicited by Ca2+, acetylcholine, norepinephrine, ATP, and direct electrical stimulation. It was concluded that transmembrane Ca2+ influx was important not only in the maintenance of tone and spontaneous phasic muscle activity, but also for the activation of contractions induced by all of the stimulants tested. The data also suggest that intracellular Ca2+ fraction(s) participate in the contractile responses to acetylcholine and norepinephrine challenge, but not to contractions evoked by ATP or electricity.     

Modulation of Ca2+ sensitivity regulates contractility of rabbit corpus cavernosum smooth muscle

PURPOSE: We examined the role of the modulation of Ca2+ sensitivity for regulating the contractility of corpus cavernosum smooth muscle. MATERIALS AND METHODS: We applied simultaneous measurements of intracellular Ca2+ concentration and tension in fura-PE3 loaded intact strips and receptor coupled permeabilization by alpha-toxin. RESULTS: In intact fura-PE3 loaded strips the tension induced by 10 microM. phenylephrine was significantly greater than that produced by depolarization with 118 mM. K+, although the extent of intracellular Ca2+ concentration elevations was similar. During sustained contraction induced by 10 microM. phenylephrine the application of 10 microM. Y-27632 (a Rho kinase inhibitor) induced relaxation with a slight decrease in intracellular Ca2+ concentration, while the application of 3 microM. GF109203X (a protein kinase C inhibitor) induced relaxation without changing intracellular Ca2+ concentration. In alpha-toxin permeabilized strips 10 microM. phenylephrine induced a larger increase in force at a constant intracellular Ca2+ concentration and produced a leftward shift in the intracellular Ca2+ concentration-tension relationship, a response that was partially inhibited by pretreatment with Y-27632 or GF109203X. CONCLUSIONS: These results indicate that in rabbit corpus cavernosum smooth muscle phenylephrine induces contraction not only by increasing intracellular Ca2+ concentration, but also by increasing Ca2+ sensitivity of the contractile apparatus in a Rho kinase and protein kinase C dependent manner. Antagonism of Ca2+ sensitization pathways in the corpus cavernosum smooth muscle represents an alternate target for the treatment of erectile dysfunction.     

Foregut smooth muscle reactivity changes in the hydrocephalus-induced infantile rats

BACKGROUND: An association between hydrocephalus and gastroesophageal motor abnormalities that cause gastroesophageal reflux (GER) is well known. Our aim was to investigate hydrocephalus-induced alterations in esophageal and gastric smooth muscle reactivity and their modulation by pharmacological interventions in the rat model. MATERIALS AND METHODS: Hydrocephalus was induced in infantile rats by injection of kaolin into the cisterna magna. Hydrocephalic and sham-operated rats were exsanguinated 2 weeks after surgery. Esophageal and gastric fundus smooth muscle strips were studied in vitro for their contractile and relaxant response to receptor activation in the organ chambers set up. Additionally, esophageal and gastric tissue specimens were examined histologically for GER-induced changes. RESULTS: No histological evidence of esophageal and gastric changes reflecting GER was observed in the specimens of the control and hydrocephalus-induced rats. Maximum contractile responses of esophageal and gastric fundus smooth muscle to KCl and muscarinic receptor agonist carbachol were increased in the hydrocephalic groups compared with the control groups. These changes were statistically significant. Relaxant responses to beta adrenoceptor agonist isoprenaline were similar in the esophageal muscle strips of both hydrocephalic groups and the control groups. However, isoprenaline-induced relaxant responses of the gastric fundus muscle strips in the hydrocephalus-induced groups were significantly decreased as compared with the control groups. The relaxant responses to papaverine in the esophageal and gastric fundus smooth muscle strips were similar in the two groups. CONCLUSIONS: Our study revealed alterations of receptor-dependent and receptor-independent foregut smooth muscle reactivity in the hydrocephalus-induced rat pups. Therefore, we suggest that impaired smooth muscle reactivity at least in part may contribute to abnormalities of foregut motor function seen in patients with hydrocephalus.     

Increased expression of endothelin B receptors in the diabetic rabbit urinary bladder: functional relevance

OBJECTIVES: To determine the effect of diabetes mellitus on the density and distribution of endothelin A (ETA ) and endothelin B (ETB ) receptor subtypes in the rabbit urinary bladder, and to assess the in vitro functional properties of endothelin-1 (ET-1) receptors in bladder smooth muscle strips from diabetic and healthy rabbits. MATERIALS AND METHODS: Diabetes mellitus was induced in six male New Zealand White rabbits with alloxan and their urinary bladders excised 6 months after the induction of diabetes. On serial detrusor and bladder neck sections, low- and high-resolution autoradiography was performed using radioligands for ET-1, ETA and ETB receptors; these sections were then analysed densitometrically. The results were compared with those from six age-matched healthy control rabbits. Functional responses were investigated using isometric tension studies. RESULTS: ETA and ETB receptor binding sites were localized to both the urothelium and smooth muscle of the detrusor and bladder neck. There were significantly more ETB receptor binding sites in the diabetic detrusor and bladder neck sections than in controls. ET-1 smooth muscle contractile responses were ETA receptor-mediated. The smooth muscle contractile responses to ET-1 were unaltered in the detrusor, but significantly impaired in the bladder neck of diabetic animals compared with controls. CONCLUSION: Alteration in the expression of ETB receptors and in vitro contractile smooth muscle responses to ET-1 in the diabetic rabbit urinary bladder neck may play a role in the pathophysiology of diabetic cystopathy.     

Altered in vitro adrenergic responses of dog detrusor msucle after chronic bladder outlet obstruction.

Muscle strips from the bladder body and dome of normal and control dogs usually demonstrate a relaxing (beta-adrenergic) response to norepinephrine. After bladder outlet obstruction was caused by urethral constriction, all body muscle strips from 7 of 12 dogs (58 per cent) demonstrated contractile (alpha-adrenergic) responses to norepinephrine. Bladder base muscle strips continued to show alpha-adrenergic responses. Desensitization or decreased beta-adrenergic receptor activity may play a part in causing the low compliance and detrusor instability seen in patients with bladder outlet obstruction.