Aging-associated prostate smooth muscle hypercontractility in rats

Abstract Benign prostatic hyperplasia (BPH) is a multifactorial disease, highly associated with aging and characterized by increased prostate smooth muscle (PSM) contractility. Animal models have been employed to explore the aging-associated PSM hypercontractility; however, studies have focused in old animals, neglecting the initial alterations in early ages. The determination of prostatic dysfunctions onset is crucial to understand the BPH pathophysiology and to propose new BPH treatments. Considering that PSM contractility in 10-month-old rats has already been explored, the aim of the present study was to characterize the PSM contractility in younger rats. Male Wistar control (3.5-month-old), 6- and 8-month-old rats were used. Concentration-response curves to phenylephrine and electrical-field stimulation (EFS) were conducted in prostate from all groups. For the first time, we showed that 6- and 8-month-old rats exhibit PSM hypercontractility. The increased prostate contractility to phenylephrine starts around at 6-month-old, worsening during the aging. The 8-month-old rats exhibited hypercontractility to phenylephrine and EFS compared to the control and 6-month-old groups. Reduced phenylephrine potency was observed in 8-month-old rats, indicating an increased age-dependent prostate sensibility to this agonist. Collectively, our findings support the use of 6- and 8-month-old aged rats as new models to explore prostate hypercontractility in BPH.

A Direct Inhibitory Effect of Botulinum Toxin Type A on Antral Circular Muscle Contractility of Guinea Pig

PURPOSE: Recent studies suggest new mechanisms of Botulinum toxin (BoNT) other than inhibiting acetylcholine (ACh) release from nerve terminals. The aim of this study was to determine whether other mechanisms for BoNT exist, so that it directly inhibits smooth muscle contraction. MATERIALS AND METHODS: Guinea pig antral muscle strips were studied in vitro after 2 hours of exposure to Botulinum toxin type A (BoNT/A). Contractile responses to electric field stimulation (EFS), high K+ (60 mM) and ACh (100 microM) were evaluated 24 and 48 hours after antral intramuscular injection of BoNT/A or vehicle. RESULTS: BoNT/A inhibited muscular contraction caused by high K+ and ACh. Contractile responses to low (1 & 4 Hz) and high (8 & 20 Hz) frequency EFS of antral muscle strips 24 and 48 hours after antral intramuscular injection of BoNT/A were significantly inhibited. CONCLUSION: The ability of BoNT/A to directly inhibit antral muscular contractility suggests a new mechanism for the pharmacologic actions of BoNT-direct inhibition of muscular contraction.

MLCK and PKC Involvements via Gi and Rho A Protein in Contraction by the Electrical Field Stimulation in Feline Esophageal Smooth Muscle

We have shown that myosin light chain kinase (MLCK) was required for the off-contraction in response to the electrical field stimulation (EFS) of feline esophageal smooth muscle. In this study, we investigated whether protein kinase C (PKC) may require the on-contraction in response to EFS using feline esophageal smooth muscle. The contractions were recorded using an isometric force transducer. On-contraction occurred in the presence of NG-nitro-L-arginine methyl ester (L-NAME), suggesting that nitric oxide acts as an inhibitory mediator in smooth muscle. The excitatory composition of both contractions was cholinergic dependent which was blocked by tetrodotoxin or atropine. The on-contraction was abolished in Ca2+-free buffer but reappeared in normal Ca2+-containing buffer indicating that the contraction was Ca2+ dependent. 4-aminopyridine (4-AP), voltage-dependent K+ channel blocker, significantly enhanced on-contraction. Aluminum fluoride (a G-protein activator) increased on-contraction. Pertussis toxin (a Gi inactivator) and C3 exoenzyme (a rhoA inactivator) significantly decreased on-contraction suggesting that Gi or rhoA protein may be related with Ca2+ and K+ channel. ML-9, a MLCK inhibitor, significantly inhibited on-contraction, and chelerythrine (PKC inhibitor) affected on the contraction. These results suggest that endogenous cholinergic contractions activated directly by low-frequency EFS may be mediated by Ca2+, and G proteins, such as Gi and rhoA, which resulted in the activation of MLCK, and PKC to produce the contraction in feline distal esophageal smooth muscle.

P2X and P2Y Receptors Mediate Contraction Induced by Electrical Field Stimulation in Feline Esophageal Smooth Muscle

It is well-known that electrical field stimulation (EFS)-induced contraction is mediated by a cholinergic mechanism and other neurotransmitters. NO, ATP, calcitonin gene-related peptide (CGRP), and substance P are released by EFS. To investigate the purinergic mechanism involved in the EFS-induced contraction, purinegic receptors antagonists were used. Suramine, a non-selective P2 receptor antagonist, reduced the contraction induced by EFS. NF023 (10(-7)~10(-4) M), a selective P2X antagonist, inhibited the contraction evoked by EFS. Reactive blue (10(-6)~10(-4) M), selective P2Y antagonist, also blocked the contraction in a dose-dependent manner. In addition, P2X agonist alpha,beta-methylene 5'-adenosine triphosphate (alphabetaMeATP, 10(-7)~10(-5) M) potentiated EFS-induced contraction in a dose-dependent manner. P2Y agonist adenosine 5'-[beta-thio]diphosphate trilithium salt (ADPbetaS, 10(-7)~10(-5) M) also potentiated EFS-induced contractions in a dose-dependent manner. Ecto-ATPase activator apyrase (5 and 10 U/ml) reduced EFS-induced contractions. Inversely, 6-N,N-diethyl-D-beta,gamma-dibromomethylene 5'-triphosphate triammonium (ARL 67156, 10(-4) M) increased EFS-induced contraction. These data suggest that endogenous ATP plays a role in EFS-induced contractions which are mediated through both P2X-receptors and P2Y-receptors stimulation in cat esophageal smooth muscle.

Alteration of nitrergic neuromuscular transmission as a result of acute experimental colitis in rat

Nitric oxide (NO) is a non-adrenergic, non-cholinergic neurotransmitter found in the enteric nervous system that plays a role in a variety of enteropathies, including inflammatory bowel disease. Alteration of nitrergic neurons has been reported to be dependent on the manner by which inflammation is caused. However, this observed alteration has not been reported with acetic acid-induced colitis. Therefore, the purpose of the current study was to investigate changes in nitrergic neuromuscular transmission in experimental colitis in a rat model. Distal colitis was induced by intracolonic administration of 4% acetic acid in the rat. Animals were sacrificed at 4 h and 48 h postacetic acid treatment. Myeloperoxidase activity was significantly increased in the acetic acid-treated groups. However, the response to 60 mM KCl was not significantly different in the three groups studied. The amplitude of phasic contractions was increased by Nomega-nitro-L-arginine methyl ester (L-NAME) in the normal control group, but not in the acetic acid-treated groups. Spontaneous contractions disappeared during electrical field stimulation (EFS) in normal group. However, for the colitis groups, these contractions initially disappeared, and then reappeared during EFS. Moreover, the observed disappearance was diminished by L-NAME; this suggests that these responses were NO-mediated. In addition, the number of NADPH-diaphorase positive nerve cell bodies, in the myenteric plexus, was not altered in the distal colon; whereas the area of NADPH-diaphorase positive fibers, in the circular muscle layer, was decreased in the acetic acidtreated groups. These results suggest that NO-mediated inhibitory neural input, to the circular muscle, was decreased in the acetic acid-treated groups.

Relaxing Effects of Isoproterenol and Nitric oxide on the Contractile responses of the Rat Bladder Muscle Strip

No abstract available.

Role of Nitric Oxide in the Relaxation of Rabbit Vaginal Smooth Muscle / 대한비뇨기과학회지

PURPOSE: Vaginal engorgement depends, in part, on the relaxation of vaginal smooth muscle. The aim of this study was to evaluate the role of nitric oxide(NO) in the relaxation of the vaginal smooth muscle. MATERIALS AND METHODS: New Zealand White female rabbits(n=8) were sacrificed and distal 1/3 of the vagina was dissected. Strips of vaginal tissues were immediately processed for isometric tension measurement in the organ bath. The vaginal strips were precontracted with phenylephrine and the responses to electrical field stimulation(EFS) or sodium nitroprusside were examined. Each preparations was also processed immunohistochemically to determine the presence of neuronal NO synthase(n-NOS) in the tissue. RESULTS: EFS caused a frequency-dependent relaxation, which was significantly inhibited in the presence of Nw-nitro-L-arginine methyl ester(L-NAME), a competitive inhibitor of NOS. Sodium nitroprusside, a NO donor, caused concentration-dependent relaxations in the vaginal tissue and the relaxation was not affected by L-NAME(10-4M). n-NOS immunoreactivity was detected in perivascular space and vicinity of vaginal smooth muscle. CONCLUSIONS: These results suggest that the relaxation of the rabbit vaginal smooth muscle is partly mediated by the NO pathway.

Contractile Response of the Rat Vas Deferens to Electrical Field Stimulation, Phenylephrine and Acetylcholine under Hypoxia / 대한비뇨기과학회지

PURPOSE: The proper functioning of all smooth muscle structures depends on the ability of normal blood to deliver oxygen and nutrients to the muscles. In addition, hypoxia has been shown to inhibit the contractile response to various forms of stimulation. The contractile response of the vas deferens can be divided into two phases: an initial rapid increase in tension(phasic contraction) and prolonged period of sustained tension(tonic contraction). The aim of this study was to determine the effect of hypoxia on the ability of the vas deferens to sustain tension . MATERIALS AND METHODS: The isolated strips of rat vas deferens were studied for Isometric tension measurement under normoxia and hypoxia in the organ chamber. Effects of phenylephrine(Phe) and acetylcholine(Ach) on the rat vas deferens tissue were monitored under normoxia and hypoxia. RESULTS: The results of these studies can be summerized as follows; (1) hypoxia induced time dependent decrease in both phasic and tonic contraction in response to electrical field stimulation(4 and 32Hz). The rate of inhibition of the tonic contraction was significantly and immediatly greater than that of the phasic contraction in both the prostatic and epididymal vas deferens, which was much prominent. (2) hypoxia(5min) increased the basal tension of prostatic vas deferens only to Phe(10(-3)M) and Ach(10(-3)M). But In the response of epididymal vas deferens to Phe(10(-3)M) and Ach(10(-3)M), rhythmic contractions disappeared. CONCLUSIONS: In conclusion, the contractile response of rat Vas deferens to electrical field stimulation under hypoxia were decreased and basal tension of prostatic vats deferens to Phe(10(-3)M) or Ach(10(-3)M) was increased This effect can interfere the sperm expulsion by changing normal contractability of the vas deferens.

The Effect of Electrical Field Stimulation and alpha-Adrenergic Agonist on the Contraction of Vas Deferens after Vasectomy in the Rat / 대한비뇨기과학회지

This study was designed to determine the effect of electrical field stimulation (EFS) and adrenergic agonist on the contractility of vasectomized prostatic and epididymal segments at postvasectomized 2, 5 and 10 weeks, and to observe innervation changes of the vas deferens after vasectomy. The contractile response was recorded on a polygraph via force transducer and expressed as the g tension per 100 mg tissue. And we reviewed histopathologic sections stained with S-100 protein by light microscopy. The results were as follows: 1. In control groups, contractile responses of prostatic and epididymal segments to EFS (4, 8, 16, 32 &64 Hz) were gradually increased by increasing frequencies. But contractile responses of vasectomized epididymal segments to all frequencies of EFS declined. Contractile responses of vasectomized prostatic segments were significantly greater than that of vasectomized epididymal segments (p<0.05). 2. Contractile responses of epididymal segments to phenylephrine hydrochloride 0.00001M were significantly greater than that of prostatic segments (p<0.05). Contractile responses of prostatic segments were tend to decline. In epididymal segments, contractile response of post-vasectomized 5 weeks group was significantly greater than that of control and post-vasectomized 2 weeks groups (p<0.05). 3. In control and vasectomized prostatic segment, nerve bundles were strongly positive and intact histopathologically for the S-100 protein immunohistochemical stain. In epididymal segment, nerve bundles were intact in control group. However, vacuolar degeneration tend to be gradually increased and stained weakly by increasing duration in vasectomized epididymal segment. These results suggest that the progression of degenerative change of adrenergic innervation after vasectomy may play an important role in progressively decreasing contractility of the vas deferens after vasectomy.

Effects of Electrical Field Stimulation of the Isolated Corpus Cavernosum from Hypertensive Rats / 대한비뇨기과학회지

The present study was aimed to investigate whether and to what extent hypertension affects the relaxation of the corpus cavernosum. The corpus cavernosum was isolated from 12-week 2- kidney, 1-clip hypertensive rats. The corporal strips were isolated and suspended longitudinally in an organ bath. They were precontracted with phenylephrine, and their responses to electrical field stimulation (EFS) were examined. EFS caused a frequency-dependent contraction (60%) or relaxation (40%) of the corpus cavernosum precontracted with phenylephrine. The contraction response was inhibited or abolished and only frequency-dependent relaxation appeared in the presence of atropine (0.00001mol/L) and guanethidine (0.00001mol/L). The relaxation response to EFS of the corporal preparation precontracted with phenylephrine was attenuated or abolished in the presence of L-NAME (0.0001mol/L). The corporal preparation from the hypertensive rats also showed a frequency-dependent relaxation, however, the degree of which was lower at a low frequency of stimulation than that from the normotensive control. These results suggest that endothelium-derived nitric oxide released upon neural stimulation partly mediate the relaxation of the corpus cavernosum. It is also suggested that hypertension is associated with a partly attenuated relaxation response to EFS.