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.     

In vitro rat bladder function after neonatal estrogenization

PURPOSE: Experiments were done to evaluate the functional effects of neonatal diethylstilbestrol (DES) treatment on bladder function in male and female Noble rats. MATERIALS AND METHODS: At 5 months after neonatal DES bladders were removed and weighed. Ventral and dorsal bladder strips were prepared to evaluate the effects of neonatal DES on contractile responses to electrical field stimulation, carbachol, adenosine triphosphate, phenylephrine and KCl. Relaxant responses to the catecholamines arterenol (norepinephrine), epinephrine and isoproterenol were also monitored. RESULTS: Neonatal DES resulted in significant increases in bladder mass in males and females. Contractile and relaxant responses were largely unchanged by neonatal DES treatment and the only change observed was a decreased response of ventral strips from male neonatal DES rats to 4 and 8 Hz. stimulation. Ventral strips from male control and neonatal DES rats responded to field stimulation and carbachol with significantly greater responses than dorsal strips and were more sensitive to the relaxant actions of norepinephrine and epinephrine. CONCLUSIONS: The data confirm that neonatal DES causes infravesical obstruction. However, in contrast to published reports of the effects of surgically induced mild outlet obstruction, neonatal DES treatment has little effect on in vitro bladder strip contractile or relaxant function. Thus, the neonatal DES treated rat does not seem to be a useful model in which to study the in vitro effects of partial outlet obstruction on the bladder.     

Direct effect of amezinium on rabbit urethra: Effect of estrogen and progesterone treatment

The effect of amezinium, a new antihypotensive agent, and hormonal treatment on the female rabbit urethra was investigated. Cumulative dose responses were obtained for amezinium and norepinephrine on strips of muscle from the urethras of ovariectomized female rabbits by means of the tissuebath system. Amezinium enhanced the response to electrical field stimulation and showed a direct contractile response on the urethra. These responses were only about 20% of the maximum norepinephrine response. The contractile response to amezinium was completely blocked by prazosin. When rabbits were pretreated with estrogen, with or without progesterone, for 4 weeks, the response to amezinium increased to 40% of the maximum norepinephrine response. Although amezinium enhances muscle contractile responses to electrical stimulation, this effect is strong when amezinium is used alone; concurrent estrogen treatment improves the effects of amezinium.EDITORIAL COMMENT The authors present their initial investigation on the effect of amezinium on the tone of female rabbit urethral muscle. The study is well designed, using classical experimental methodology. The investigators show that amezinium has a moderate contractile effect on female rabbit urethral muscle strips. This effect is blocked by the addition of prazosin, a direct adrenergic antagonist, resulting in urethral muscular relaxation. The effect of amezinium is enhanced by pretreatment with estrogen, either alone or in combination with progesterone. Pretreatment with progesterone has no significant impact on the urethral muscular contraction caused by amezinium. Amezinium has been used in human studies for the treatment of hypotension, and appears to be well tolerated. Only further extensive investigation will show whether this interesting compound has clinical use in the treatment of female genuine stress urinary incontinence.     

Pretreatment with phenoxybenzamine attenuates the radial artery's vasoconstrictor response to alpha-adrenergic stimuli

BACKGROUND: Although the radial artery bypass conduit has excellent intermediate-term patency, it has a proclivity to vasospasm. We tested the hypothesis that brief pretreatment of a radial artery graft with the irreversible adrenergic antagonist phenoxybenzamine attenuates the vasoconstrictor response to the vasopressors phenylephrine and norepinephrine compared with the currently used papaverine/lidocaine. METHODS: Segments of human radial artery grafts were obtained after a 30-minute intraoperative pretreatment with a solution containing 20 mL of heparinized blood, 0.4 mL of papaverine (30 mg/mL), and 1.6 mL of lidocaine (1%). The segments were transported to the laboratory and placed into a bath containing Krebs-Henseleit solution and 10, 100, or 1000 micromol/L phenoxybenzamine or vehicle. The segments were tested in organ chambers for contractile responses to increasing concentrations of phenylephrine and norepinephrine (0.5-15 micromol/L). RESULTS: Contractile responses to 15 micromol/L phenylephrine in control radial artery segments averaged 44.2% +/- 9.1% of the maximal contractile response to 30 mmol/L KCl. Papaverine/lidocaine modestly attenuated contraction to 15 micromol/L phenylephrine (32.1% +/- 5.9%; P =.22), but 1000 micromol/L phenoxybenzamine completely abolished radial artery contraction (-7.2% +/- 4.4%; P <.001). The effect of 10 and 100 micromol/L phenoxybenzamine on attenuating vasocontraction was intermediate between 1000 micromol/L phenoxybenzamine and papaverine/lidocaine. Responses to 15 micromol/L norepinephrine in control radial artery segments averaged 54.7% +/- 7.5% of maximal contraction to 30 mmol/L KCl. Papaverine/lidocaine modestly attenuated the contraction response of radial artery segments (35.6% +/- 5.1%; P =.04). In contrast, 1000 micromol/L phenoxybenzamine showed the greatest attenuation of norepinephrine-induced contraction (-10.5% +/- 2.0%; P <.001). CONCLUSIONS: A brief pretreatment of the human radial artery bypass conduit with 1000 micromol/L phenoxybenzamine completely attenuates the vasoconstrictor responses to the widely used vasopressors norepinephrine and phenylephrine. Papaverine/lidocaine alone did not block vasoconstriction to these alpha-adrenergic agonists.     

The effect of hydrocephalus on lower esophageal sphincter smooth muscle reactivity: experimental study

Purpose

The aim of this study was to assess the pharmacophysiological significance of the enteric nervous system for the mechanical responses of lower esophageal sphincter (LES) in infantile rats with kaolin-induced hydrocephalus.

Material and methods

Hydrocephalus was created in 7-day-old rats by injection of kaolin into the cisterna magna. After 10 days, rats were decapitated. Contractile (KCl, carbachol) and relaxant (isoprenaline, papaverine) responses were determined by using in vitro muscle technique in isolated LES smooth muscle strips.

Results

The receptor-mediated contractile and relaxant response to carbachol and isoprenaline in the LES smooth muscle was impaired in rats with hydrocephalus. There was no significant difference in the KCl and papaverine response in hydrocephalic and sham operated rats.

Conclusion

Our findings suggest that hydrocephalus may impair receptor-mediated contractile and relaxant activity of LES smooth muscle leading to gastroesophageal reflux.     

Functional response of bladder strips from streptozotocin diabetic rats depends on bladder mass

PURPOSE: We investigated the relationship of bladder mass to responses to electrical field stimulation and adrenergic agonists in diabetic rat bladders. MATERIALS AND METHODS: Longitudinal strips were removed from the ventral and dorsal detrusor of age matched control, 2-month diabetic and sucrose drinking rats. Contractile responses to electrical field stimulation, KCl and phenylephrine, and relaxation in response to norepinephrine and isoproterenol were measured. RESULTS: Bladders from sucrose drinking and diabetic rats weighed significantly more than those of controls. Diabetic rats were divided into 2 groups with the bladder weighing less than or greater than 265 mg. Strips from small diabetic bladders were generally more responsive to field stimulation and norepinephrine than those from control or sucrose drinking rats. Conversely decreased function was especially apparent in dorsal strips from large diabetic bladders. Ventral strips were significantly more sensitive to the relaxant actions of norepinephrine and isoproterenol than dorsal strips. CONCLUSIONS: Our results suggest that the responsiveness of diabetic rat bladder to electrical field stimulation and adrenergic agonists is related to bladder mass, analogous to observations after partial outlet obstruction. Decreased function was particularly apparent in dorsal strips from diabetic rats with a large bladder.     

Effects of prostaglandin E1 on isolated dog renal artery

Actions of prostaglandin (PG) E1 were investigated using isolated dog renal arterial strips. Norepinephrine increased the tension of the renal arterial strips contracted with potassium, and this response was depressed by phentolamine. Isoproterenol produced relaxant effects on these arteries, and this response was converted to contractile one by propranolol. Diltiazem dose dependently relaxed the potassium-contracted strips. PGE1 (10(-9)-3 X 10(-8) Gm./ml.) constricted the renal arterial strips, while in higher concentrations (10(-7)-3 x 10(-7) Gm./ml.) it caused relaxations of them. Contractile responses by PGE1 were not affected by phentolamine or phenoxybenzamine, but were suppressed by diltiazem. On the other hand, relaxant effects of PGE1 were not changed by propranolol. Papaverine or theophylline significantly inhibited the contractions induced by PGE1. From these results it is suggested that (1) in the dog renal artery adrenergic alpha-receptors must be more dominant than beta-receptors; (2) PGE1 will produce a depolarization of renal arterial smooth muscle and/or increase an active transport of calcium ions into smooth muscle cells; and (3) the relaxant responses by PGE1 may be related to an increase in cellular cyclic adenosine monophosphate (AMP) contents.     

The effects of melatonin on ischemia-reperfusion induced changes in rat corpus cavernosum

PURPOSES: We determined the change in contractile activity and oxidant damage after ischemia-reperfusion of rat corpus cavernosum and investigated the effects of melatonin (Sigma Chemical Co., St. Louis, Missouri) on these parameters. MATERIALS AND METHODS: The abdominal aorta of male Wistar albino rats was occluded to induce ischemia-reperfusion. Melatonin (10 mg./kg.) or vehicle (1% alcohol in saline per kg.) was administered subcutaneously before ischemia-reperfusion. In the sham operated control group the abdominal aorta was left intact and the rats were treated with melatonin or vehicle. After decapitation corporeal tissues were placed in organ baths or stored for biochemical measurements. RESULTS: In sham operated rats phenylephrine added cumulatively caused a concentration dependent contraction in corpus cavernosum strips precontracted with KCl and acetylcholine added cumulatively to strips precontracted with phenylephrine caused a dose dependent relaxation response. In the ischemia-reperfusion group contraction and relaxation responses decreased significantly compared within controls. Melatonin treatment in the ischemia-reperfusion group reversed these responses. Myeloperoxidase activity and the lipid peroxidation level of the corporeal tissues in the ischemia-reperfusion group were significantly higher than in the sham operated control group. Melatonin treatment in the ischemia-reperfusion group decreased myeloperoxidase activity and the lipid peroxidation level compared with ischemia-reperfusion alone, whereas melatonin treatment alone had no significant effect on these parameters. CONCLUSIONS: In this study the corporeal tissues of rats exposed to ischemia-reperfusion had lower responses to contractile and relaxant agents than those of sham operated rats. Treatment with melatonin before ischemia-reperfusion almost completely reversed smooth muscle responses and prevented the increased myeloperoxidase activity and lipid peroxidation of corporeal tissues.     

Effects of phosphodiesterase type 5 inhibitor on the contractility of prostate tissues and urethral pressure responses in a rat model of benign prostate hyperplasia

AIM: This study was performed to investigate the effect of DA-8159, a selective phosphodiesterase 5 (PDE5) inhibitor, on benign prostatic hyperplasia (BPH) both in vitro and in vivo. METHODS: We assessed the influence of DA-8159 on the contractility of rat prostate tissues in an organ-bath experiment. In addition, in order to investigate whether chronic administration of DA-8159 prevents the increase of electrostimulation-induced intraurethral pressure (IUP) responses associated with BPH, BPH was induced by steroid hormones (testosterone plus 17beta-estradiol) and DA-8159 (5, 20 mg/kg) was concomitantly administered once a day for 8 weeks. After that the electrostimulation-induced IUP responses were measured. Finally, we investigated the acute treatment effect of DA-8159 on IUP responses in an established BPH model after a single intravenous injection of DA-8159 (0.3, 1 mg/kg). RESULTS: DA-8159 concentration-dependently reduced the contraction of the isolated prostate strips with an IC50 value of 70 microM. In chronic treatment study, while the BPH control rats showed a significantly increased IUP both at the baseline and by electrostimulation, the chronic DA-8159 treatment significantly attenuated the increase in IUP responses in a dose- and frequency-dependent manner. In the acute treatment study, a single intravenous injection of DA-8159 also prevented the increase in urethral pressure in a dose-dependent manner. CONCLUSIONS: These results suggest that DA-8159 may be beneficial on lowering the urethral pressure associated with BPH via dilatation of the prostate, but a further evaluation of the efficacy on humans needs to be performed.     

Response of the fetal sheep bladder to urinary diversion

PURPOSE: In adults urinary diversion results in bladder atrophy and a rapid decrease in contractile function. Little is known about the effects of urinary diversion on bladder development. In this regard we characterized the responses of fetal sheep bladder strips obtained from animals that underwent urinary diversion. MATERIALS AND METHODS: Urinary diversion was performed on fetal sheep after 90 days of gestation (term 147 days) and bladder tissue was obtained 2 weeks later. Contractile and relaxant responses of full-thickness bladder strips were tested. RESULTS: Bladders from fetal sheep subjected to urinary diversion weighed significantly less than control fetal bladders. Histological studies demonstrated marked connective tissue infiltration and the reorganization of smooth muscle elements. Carbachol stimulated a tonic contraction, while field stimulation administered during the tonic contraction elicited a phasic relaxation or a biphasic response, consisting of an initial relaxation and then a phasic contraction in control and diverted bladders. Contractile responses of defunctionalized strips to carbachol were significantly less than those of control bladder strips. Contractile responses of defunctionalized bladder strips to field stimulation at 1 Hz. were significantly greater than those of control strips. Responses of the 2 sets of fetal bladder strips to higher frequencies were similar, as were the contractile responses to adenosine triphosphate and KCl. Field stimulated relaxations in the presence of carbachol stimulated contraction of defunctionalized bladder strips were significantly greater than those of control strips, while the relaxant responses of each set of fetal bladder strips to isoproterenol and nitroprusside were similar. CONCLUSIONS: Urinary diversion in normal fetal sheep resulted in marked structural changes, reduced carbachol stimulation and increased field stimulation relaxation.     

Effects of aminoguanidine and N(omega)-nitro-L-arginine methyl ester on vascular hyporeactivity induced by endotoxaemia.

OBJECTIVE: To investigate the effects of endotoxaemia on the reactivity of the aortic bed in rats, and to compare the effects of the nitric oxide (NO) synthase inhibitors aminoguanidine and N(omega)-nitro-L-arginine methyl ester (L-NAME), on endotoxaemia-induced changes in vascular reactivity. DESIGN: Randomised experiment. SETTING: University laboratory, Turkey. SUBJECTS: 54 Wistar rats. INTERVENTIONS: Rats were divided into control (n = 24) and endotoxaemia (n = 30) groups and were treated with an intraperitoneal injection of saline (control) and lipopolysaccharide (20 mg/kg), respectively. Subgroups of control and endotoxaemic rats were given either aminoguanidine or L-NAME by the same route. MAIN OUTCOME MEASURES: Contractile responses to phenylephrine and relaxation responses to acetylcholine 4 hours after treatment. RESULTS: Incubation with aminoguanidine and L-NAME potentiated the phenylephrine-induced contractile response and inhibited acetylcholine-induced relaxation in aortic rings in the control group. The vascular responses to phenylephrine and acetylcholine were less pronounced in the endotoxaemia group, and in vitro incubation with aminoguanidine and L-NAME partially restored the contraction induced by phenylephrine but did not affect the impaired response to acetylcholine. Aminoguanidine given in vivo prevented the impairment of vascular responses to both phenylephrine and acetylcholine whereas L-NAME gave no such protection. CONCLUSION: Aminoguanidine acted similarly to L-NAME when incubated with the tissues in vitro, and did not show selectivity to inducible compared with constitutive isoforms of NO synthase. The finding that aminoguanidine but not L-NAME, prevented the endotoxin-induced impairment of vascular reactivity when administrated in vivo, therefore, suggested a role other than inhibition of NO synthase.     

Effect of Mucosal Removal on the Response of the Feline Bladder to Pharmacological Stimulation

The urothelium plays an important role in the maintenance of normal bladder function. It provides a nonpermeable barrier to the contents of urine. The urothelium is directly involved in the transduction of both intravesical pressure and intravesical volume information to the afferent nerve fibers located within the lamina propria area. A third function may be to modulate bladder contractile function through local secretion of bioactive substances into the muscularis layers adjacent to the urothelium. To test this last hypothesis, the following experiments were performed: Strips of female cat bladders were isolated from the bladder body, base and urethra. The mucosa of alternate adjacent strips was removed, and the contractile response to field stimulation (FS), bethanechol (body), phenylephrine (base, urethra) and KCl was determined.For the bladder body, the strips without mucosa responded to FS, bethanechol, adenosine triphosphate (ATP) and KCl significantly greater than the strips with mucosa intact. For the bladder base and urethra, the contractile responses to FS, KCl and phenylephrine were significantly greater for the strips with mucosa removed as compared with the strips with mucosa intact. For the urethra and bladder base, FS in the presence of phenylephrine produced a relaxation. For the bladder base, the degree of FS relaxation of the isolated strips with mucosa removed was significantly greater than the strips with mucosa intact. For the urethra, FS relaxation was similar for the two groups. In conclusion, removal of the urethelium significantly and substantially increased the contractile response to FS, KCl, bethanechol and phenylephrine. Field stimulation relaxation in the bladder base was also enhanced. Thus in the cat, the mucosa has a significant inhibitory effect on the contractile response of the bladder to stimulation. The mechanism of this activity is not clear at the present time but will be the subject of further study.     

Alterations in the mechanical properties of bladder smooth muscle in hydrocephalus rat model

Objectives

It is now well established that hydrocephalus is associated with impaired bladder function. The aim of this study was to determine the effects of hydrocephalus on bladder smooth muscle (BSM) reactivity in the rat model.

Materials and Methods

Hydrocephalus was induced in 7-day-old rats by injection of kaolin into the cisterna magna (AH group). Control group rats underwent a sham operation. After 10 days, rats were decapitated. Each bladder was excised and BSM strips placed in an organ bath where contractile and relaxant responses were studied.

Results

Contractile response of BSM to KCl decreased in the AH group. Increased response to muscarinic agonist carbachol was observed in the AH group. The relaxant response to adrenergic agonist isoprenaline was significantly decreased in the AH group, whereas non-receptor-dependent agonist papaverine was unchanged in 2 groups.

Conclusion

Bladder smooth muscle reactivity is affected by the formation of hydrocephalus essentially by both receptor-dependent and non-receptor-dependent mechanisms. This pathway may be a novel target for the pharmacologic treatment of bladder dysfunction secondary to hydrocephalus.     

Physiological effects of human muscle-derived stem cell implantation on urethral smooth muscle function

The physiological effects of human muscle-derived stem cell (MDSC) implantation on urethral smooth muscle function were investigated in pudendal nerve-transected nude rats with human MDSC (TM) or saline (TS) injection into the proximal urethra compared with sham-operated, saline-injected nude rats (SS). Leak point pressure (LPP) before and after hexamethonium application, which can block autonomic efferent nerves, and proximal urethral contractile responses to carbachol and phenylephrine in muscle strip study were examined 6 weeks after the implantation. There was no significant difference between the LPPs in SS and TM. Following hexamethonium application, the LPP in TM was, however, significantly decreased compared with SS. The contractile responses to phenylephrine, but not to carbachol, in TM were significantly increased compared with SS and TS. These results suggest that the restorative effects of MDSCs are mediated by autonomic nerves and that increased sensitivity of alpha(1)-adrenoceptors may be related to restore the deficient urethral function.     

Changes in bladder function in the one year spontaneously diabetic BB rat.

Micturition characteristics and in vitro urinary bladder function were investigated in insulin-treated spontaneously diabetic BB rats and age-matched non-diabetic controls one year after the onset of diabetes. BB rats weighed less than controls and were hyperglycemic. Diabetic rats consumed larger volumes of water and excreted larger volumes of urine than controls. The frequency of micturitions and the mean volumes of urine excreted per micturition were significantly increased in BB rats compared to age-matched controls. Associated with the micturition changes in the BB rats were significant increases in bladder body mass. Contractile responses of strips from bladder bodies and bases were measured in response to nerve stimulation, carbachol, phenylephrine, ATP, and KCl. No significant differences between controls and diabetics were found in the absolute contractile responses of bladder body strips to nerve stimulation, carbachol, ATP, or KCl. However, if the data were transformed to correct for the increases in tissue mass in the diabetics, there were significant decreases in the responses of bladder body strips from BB rats to carbachol, ATP, and KCl, but not to nerve stimulation. Even after transformation, there were no differences in the responses of bladder base strips to carbachol, phenylephrine, or KCl. The data indicate that significant changes in micturition characteristics are evident one year after the onset of diabetes in the spontaneously diabetic BB rat. These changes are slow in development, since they are absent six months after the onset of diabetes. The changes in micturition and bladder strip contractility are qualitatively similar to, but quantitatively modest in comparison with those caused by streptozotocin-induced diabetes mellitus. The quantitative differences are probably attributable to an ameliorative effect of the insulin received by the BB rat.     

Age-related changes in contractile force of rabbit detrusor muscle to prostaglandin E1, E2 and F2 alpha

Contractile responses of urinary bladder muscle strips to prostaglandin (PG) E1, E2 and F2 alpha were compared in young and old rabbits. All PGs tested caused an increase in contractile force of urinary bladder muscle strips from young (3 weeks) and old (greater than 2 years) rabbits. The contractile response was most marked with PGE2 at concentrations of 10(-10)-10(-7) M in muscle strips from both young and old rabbits. At a high concentration (10(-5) M), the contractile response was most marked with PGF2 alpha in young rabbit bladder muscle strips, whereas in old rabbit bladder muscle strips the magnitude of the responses to PGE2 and PGF2 alpha were equal at 10(-6) M and both were greater than the response to PGE1. The contractile response to PGE1 was greater in old detrusor than in young detrusor at concentrations greater than or equal to 10(-6) M, whereas the contractile response to PGE2 (10(-7)-10(-5) M) and PGF2 alpha (10(-6)-10(-5) M) were greater in young detrusor than in old detrusor. These data show that rabbit detrusor muscle shows a contractile response to PGE1, E2 and F2 alpha and that the magnitude of these responses vary with age.     

Activity of angiotensin peptides in clitoral cavernosum of alloxan induced diabetic rabbit

OBJECTIVES: To assess the role of peptides of the angiotensin (ANG) on the regulation of clitoral cavernosum tone and changes in ANG binding affinity in the rabbit with diabetes mellitus. MATERIAL AND METHODS: The isometric tension measurement and in vitro autoradiography were used in sham and diabetic clitoral cavernosum. RESULTS: In tension study, contractility in response to ANG I, ANG II, ANG III and ANG IV was enhanced in diabetic clitoral cavernosum strips (EC50 was 67.6 +/- 27.2, 4.3 +/- 0.4, 189.3 +/- 37.3, 443.2 +/- 0.4 nM for diabetic versus 155.2 +/- 76.1, 38.3 +/- 0.1, 528.0 +/- 75.2, 616.9 +/- 69.5 nM for sham, respectively). Contractile responses to ANG II was significantly inhibited by type 1 ANG II receptor (AT1) antagonist but not by type 2 ANG II receptor (AT2) antagonist in both groups. Percentages in contractions by ANG II (1 nM) in the presence of Dup 753 decreased significantly 36.2 +/- 4.6 to 6.3 +/- 2.4% in sham and 56.1 +/- 7.7 to 6.0 +/- 4.8% in diabetic group. The binding affinities were enhanced in diabetic clitoral cavernosum for ANG II (dissociation constant, 4.9 +/- 1.0 for sham versus 0.9 +/- 0.2 nM for diabetic) and for ANG I, ANG III, and ANG IV (inhibitory constant, 28.6 +/- 1.5, 398.7 +/- 157.2, and 3966.5 +/- 1524.1 nM for sham versus 20.6 +/- 5.7, 78.5 +/- 23.7, and 1098.7 +/- 195.5 nM, for diabetic, respectively, all p < 0.05). Sensitivities of AT1 and AT2 receptors to ANG II enhanced in diabetic than sham clitoral cavernosum tissue. CONCLUSIONS: This results suggest that the contractile responses to all four ANG peptides are enhanced in the diabetic clitoral cavernosum. Enhancement of contractility in diabetic clitoral cavernosum may be related to the increased affinity to ANG II receptors for ANG peptides.     

Potassium channels and human corporeal smooth muscle cell tone: further evidence of the physiological relevance of the Maxi-K channel subtype to the regulation of human corporeal smooth muscle tone in vitro

PURPOSE: Recent evidence indicates that the large conductance, voltage dependent, Ca2+ sensitive K channel or Maxi-K has an important role in the modulation of human corporeal smooth muscle tone and, thus, in erectile capacity. We further clarified the contribution of the Maxi-K channel subtype to the generation of contractile responses in isolated human corporeal tissue strips. MATERIALS AND METHODS: We performed pharmacological studies of phenylephrine contracted isolated corporeal tissue strips in the presence and absence of the 2 Maxi-K channel blockers tetraethylammonium chloride (TEA) and charybdotoxin, and the Maxi-K opener NS1619. K channel treatment effects were evaluated using 2 parameters, including 1) the steady state parameter of the empirically determined peak magnitude of the steady state contractile response and 2) the kinetic parameter of time required to achieve half of the peak steady state contractile response or half-time. Electrophysiological studies in freshly isolated and cultured myocytes were performed in parallel to corroborate findings further at the tissue level. RESULTS: Pre-incubating isolated human corporeal tissue strips with 1 mM. TEA and 1 microM. charybdotoxin was associated with an approximate 20% increase in the peak steady state contractile response and a corresponding approximate 20% decrease in the half-time of the phenylephrine induced contractile response. Conversely, pre-incubation with 10 microM. NS1619 produced a significant, approximately 20% decrease in the peak steady state contractile response and an approximate 38% increase in the half-time of the phenylephrine induced contractile response. Adding 30 to 180 microM. NS1619 to phenylephrine pre-contracted smooth muscle strips resulted in a 30% to 50% reduction in steady state contractile tension. No detectable effect of NS1619 was observed in 120 mM. KCl or 100 mM. TEA pre-contracted corporeal tissue strips. Whole cell recordings of freshly isolated and cultured corporeal myocytes confirmed that 30 microM. NS1619 induced a charybdotoxin sensitive hyperpolarizing current mediated by the Maxi-K channel. CONCLUSIONS: These in vitro studies confirm and extend previous observations indicating the importance of the Maxi-K channel for regulating human corporeal smooth muscle tone, and by extension, erectile capacity and function.     

Inhibition of poly (ADP-ribose) synthetase improves pulmonary arterial endothelium-dependent relaxation after ischemic-reperfusion injury of splanchnic artery in rats

The role of poly (adenosine diphosphate-ribose) synthetase (PARS) in the contractile and relaxant responses of pulmonary arteries injured by ischemia and reperfusion (IR) of splanchnic artery has not been evaluated. We examined these responses by using 3-aminobenzamide, a pharmacological inhibitor of PARS. IR models in rats were induced by clamping the superior mesenteric artery for 60 min, followed by release of the clamp for 60 min. In the 2 treated groups, 5 or 10 mg/kg of 3-aminobenzamide was administered as an IV bolus at 10 min before reperfusion, followed by infusion rates of 5 and 10 mg.kg(-1).h(-1), respectively, during the period of reperfusion (IR + PARS inhibitor 5 and 10 groups). In the vehicle-treated group, 3-aminobenzamide was not given, but IV saline was administered (IR group). In the control group, surgery was performed, but the superior mesenteric artery was not occluded (sham group). The pulmonary arteries were isolated, and effects of drugs were evaluated in vitro. The IR group showed no attenuation of the contractile responses of the pulmonary artery to phenylephrine. The relaxant responses to endothelium-dependent vasodilators, acetylcholine, and A23187 in the IR group were significantly inhibited when compared with the sham group. The reduction in the relaxant response to endothelium-dependent vasodilators was improved in the IR + PARS inhibitor 5 and 10 groups when compared with the IR group. We concluded that IR attenuated the relaxant responses of the pulmonary artery to endothelium-dependent vasodilators and that PARS inhibitors ameliorate the reduction in the relaxant response.     

Effect of age on rabbit bladder function and structure following partial outlet obstruction

PURPOSE: We determined whether young and old rabbits respond differently to partial bladder outlet obstruction. MATERIALS AND METHODS: A total of 16 male New Zealand White rabbits were separated into 2 groups of 8 each. Group 1 consisted of young rabbits (age 7 weeks) and group 2 consisted of old rabbits (age 2 years). Four rabbits per group underwent partial outlet obstructions and 4 underwent sham operation. Four weeks following surgery individual bladder strips were used for contractile studies and the remaining tissue was examined histologically. RESULTS: Contractile responses to all forms of stimulation between the young and old sham operated groups were similar. Contractile responses to all forms of stimulation were significantly decreased to the same degree in the 2 obstructed groups. However, the rate of tension generation to field stimulation was decreased to a significantly greater degree in young vs old bladders. Although young and old bladders showed smooth muscle hypertrophy, older rabbits showed significantly greater thickening of the serosa than young rabbits. Young rabbits showed significant inflammation, hemorrhage and expansion of the lamina propria, whereas old rabbits showed none of these characteristics. CONCLUSIONS: Although there were only minor differences in the physiological response of young and old bladders to obstruction, young rabbits showed a significantly greater degree of histological damage. This may have been due to the thinner wall and greater sensitivity to distention.