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Biomedical subjects

A F Brading

Publications and source records attributed to A F Brading.

At least 73 records · Page 4Linked to original sources
PubMed1996

Urinary bladder blood flow changes during the micturition cycle in a conscious pig model.

PURPOSE: To develop a method using laser Doppler flowmetry in conscious pigs, which allows the accurate simultaneous measurement of cystometric and cardiovascular parameters together with changes in vesical blood flow. The animal model was then used to investigate the changes in blood flow in the urinary bladder which occur during the micturition cycle. MATERIALS AND METHODS: Seven large white female pigs were subjected to chronically implanted vascular access and urodynamic catheters as well as an intramural vesical laser Doppler probe. The animals underwent repeated conscious urodynamics with simultaneous measurement of cardiovascular, urodynamic and vesical blood flow parameters. RESULTS: The model shows both compliant and low-compliance behavior and allows greater investigation of the effects of intravesical pressure on blood flow. Blood flow is not altered, during compliant filling and voiding transiently decreases flow to 38% of resting levels, with a rapid return to normal. Low-compliance filling results in a progressive fall in blood flow to a minimum of 45% of normal. At all times an inverse relationship between intravesical pressure and blood flow is maintained. CONCLUSIONS: The pig model proved to be well suited to the experimental conditions and provided reproducible results. The principal determinant of blood flow within the wall of the bladder is the pressure within its lumen. During normal filling the blood supply of the bladder is able to adapt to the large increase in surface area which occurs, maintaining blood flow until the pressure increases.

Animals↗
PubMed1996

Intrinsic urethral closure mechanisms in the female pig.

This study investigates the role of the various components of the female pig urethral wall in the generation of the urethral closure pressure. Prior to voiding urethral pressure fails and this is accompanied by a rise in lamina propria blood flow. Pharmacological manipulation shows that striated muscle is not involved in the generation of the urethral closure pressure. Drugs active upon smooth muscle change urethral pressure significantly by a mechanism independent of their cardiovascular system effects. Histological studies show that it is possible to correlate the disposition of circular smooth muscle with the urethral pressure profile. In vitro smooth muscle from the high pressure zone is pharmacologically different to that from the proximal urethra in a manner which may reflect their physiological roles.

Animals↗
PubMed1995

Characteristic features of inhibitory junction potentials evoked by single stimuli in the guinea-pig isolated taenia caeci.

1. Changes in membrane potential of the guinea-pig isolated taenia caeci evoked by single stimuli have been investigated using intracellular recording techniques. Nifedipine (10 microM) was used to arrest spontaneous muscle action potentials. Single stimuli elicited complex junction potentials which consisted of both excitatory and inhibitory components. 2. The excitatory component of the compound junction potential was unaffected by hexamethonium (100 microM) but abolished by atropine (1 microM) and omega-conotoxin GVIA (10-100 nM). 3. In the presence of atropine, single stimuli elicited fast inhibitory junction potentials (IJPs). IJPs were sometimes biphasic during repolarization with a noticeable 'slow tail'. Apamin (30-100 nM) potently inhibited the fast IJP and revealed an underlying slow IJP. 4. The fast IJP was also abolished by omega-conotoxin GVIA (100 nM). However, the slow IJP was insensitive to omega-conotoxin GVIA but was abolished by cadmium (30 microM). 5. Guanethidine (3 microM) and N omega-nitro-L-arginine (10-100 microM) had no detectable effects on either of the IJPs. The dye Reactive Blue 2 reduced the amplitude of the fast IJP but this reduction was associated with a membrane hyperpolarization. 6. The existence of two distinct IJPs in the guinea-pig taenia caeci has been demonstrated. The ability of omega-conotoxin GVIA to selectively abolish the fast IJP leaving the slow IJP intact suggests that separate nerves are involved in mediating these responses.

Action Potentials↗
PubMed1995

Nitrergic inhibitory innervation of porcine rectal circular smooth muscle.

This study was performed to determine whether nitric oxide contributes to inhibitory non-adrenergic non-cholinergic (NANC) neurotransmission in the circular smooth muscle layer of pig rectum. Smooth muscle strips were mounted for isometric tension recording in superfusion organ baths. In the presence of atropine sulphate and guanethidine, transmural electrical field stimulation (EFS) produced frequency-dependent relaxation of precontracted muscle strips. N omega-nitro-L-arginine (L-NOArg), a powerful competitive antagonist of nitric oxide synthase, reduced the relaxant response in dose-dependent fashion; this response was maximally reduced by mean(s.e.m.) 86.5(2.6) per cent (P = 0.0003) at a concentration of 3 x 10(-5) mol/l L-NOArg. The response was restored by the addition of L-arginine. Sodium nitroprusside, an exogenous donor of nitric oxide, mimicked the relaxant response. Responses to EFS were abolished by tetrodotoxin. These results suggest that inhibitory NANC neurotransmission in this tissue is mediated, at least in part, by nitric oxide. The failure of L-NOArg to completely abolish the relaxant response suggests that additional neurotransmitters may be involved.

Animals↗
PubMed1995

Interaction of Ca2+ agonist and depolarization on Ca2+ channel current in guinea pig detrusor cells.

The interaction of large depolarization and dihydropyridine Ca2+ agonists, both of which are known to enhance L-type Ca2+ channel current, was examined using a conventional whole-cell clamp technique. In guinea pig detrusor cells, only L-type Ca2+ channels occur. A second open state (long open state: O2) of the Ca2+ channels develops during large depolarization (at +80 mV, without Ca2+ agonists). This was judged from lack of inactivation of the Ca2+ channel current during the large depolarizing steps (5 s) and slowly deactivating inward tail currents (= 10-15 ms) upon repolarization of the cell membrane to the holding potential (-60 mV). Application of Bay K 8644 (in 2.4 mM Ca(2+)-containing solutions) increased the amplitude of the Ca2+ currents evoked by simple depolarizations, and made it possible to observe inward tail currents (= 2.5-5 ms at -60 mV). The open state induced by large depolarization (O2*) in the Bay K 8644 also seemed hardly to inactivate. After preconditioning with large depolarizing steps, the decay time course of the inward tail currents upon repolarization to the holding potential (-60 mV) was significantly slowed, and could be fitted reasonably with two exponentials. The fast and slow time constants were 10 and 45 ms, respectively, after 2 s preconditioning depolarizations. Qualitatively the same results were obtained using Ba2+ as a charge carrier. Although the amplitudes of the inward currents observed in the test step and the subsequent repolarization to the holding potential were decreased in the same manner by additional application of nifedipine (in the presence of Bay K 8644), the very slow deactivation time course of the tail current was little changed. The additive enhancement by large depolarization and Ca2+ agonists of the inward tail current implies that two mechanisms separately induce long opening of the Ca2+ channels: i.e., that there are four open states.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1995

Regional variations in the neural control of the female pig urethra.

OBJECTIVE: To establish the regional variation, if any, in the distribution of sympathetic and parasympathetic nerves within the urethra of the female pig and to correlate this with regional variations in the response of the smooth muscle to sympathetic and parasympathetic nerve stimulation and the application of phenylephrine and carbachol. MATERIALS AND METHODS: Female pig urethras were obtained from a local abattoir. Serial sections were cut from the proximal, middle and distal regions of the urethra and stained using tyrosine hydroxylase immunohistochemistry and acetylcholinesterase histochemistry for the demonstration of sympathetic and parasympathetic nerves, respectively. Strips of smooth muscle dissected from the same regions of the urethra were also mounted in organ baths to record isometric tension. Responses to nerve stimulation and alpha-adrenoceptor and muscarinic receptor activation were recorded. RESULTS: Tyrosine hydroxylase- and acetylcholinesterase-positive staining was demonstrated throughout the urethra. However, the density of sympathetic innervation was greatest in those strips dissected from the distal urethra, whilst the parasympathetic innervation was uniform throughout the length. Strips of urethral smooth muscle mounted for tension recording generated spontaneous tone. Smooth muscle dissected from the proximal urethra developed the greatest tone, whilst strips from the distal urethra generated significantly less. Responses to nerve stimulation were complex; sympathetic nerve stimulation elicited frequency-dependent contraction in all strips, but the response was most pronounced in the distal strips where tone was low. Conversely, parasympathetic nerve stimulation elicited the greatest contractile response from the proximal urethral strips. In all strips, but in particular those dissected from the proximal urethra, the contractile responses were attenuated by the occurrence of a non-adrenergic, non-cholinergic (NANC), non-nitrergic relaxation as stimulation frequency was increased. Phenylephrine and carbachol also produced concentration-dependent contraction of all urethral strips. Like the nerve-mediated responses, contraction in response to phenylephrine was most pronounced in the distal urethral strips whilst the response to carbachol was most pronounced in the proximal urethral strips. CONCLUSIONS: The results demonstrated a regional variation in the distribution of sympathetic nerves within the urethra of the female pig which would appear to be mirrored not only in the responsiveness of the tissue to sympathetic nerve stimulation but also in its response to alpha-adrenoceptor stimulation. In contrast, although no regional variation in the distribution of parasympathetic nerves could be demonstrated histologically, responses to nerve stimulation and the muscarinic agonist carbachol were most pronounced in the proximal urethral strips.

Acetylcholinesterase↗
PubMed1995

Factors involved in the relaxation of female pig urethra evoked by electrical field stimulation.

1. Non-adrenergic, non-cholinergic (NANC) relaxations induced by electrical field stimulation (EFS) were studied in pig isolated urethra. The mechanism for relaxation was characterized by measurement of cyclic nucleotides and by study of involvement of different subsets of voltage-operated calcium channels (VOCCs). 2. EFS evoked frequency-dependent and tetrodotoxin-sensitive relaxations in the presence of propranolol (1 microM), phentolamine (1 microM) and scopolamine (1 microM). At low frequencies (< 12 Hz), relaxations were rapid, whereas at high (> 12 Hz) frequencies distinct biphasic relaxations were evoked. The latter consisted of a rapidly developing first phase followed by a more long-lasting second phase. 3. Treatment with the NO-synthesis inhibitor NG-nitro-L-arginine (L-NOARG; 0.3 mM) inhibited relaxations at low frequencies of stimulation. At high frequencies (> 12 Hz) only the first relaxation phase was affected. 4. Measurement of cyclic nucleotides in preparations subjected to continuous nerve-stimulation, revealed an increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels from 1.3 +/- 0.3 to 3.0 +/- 0.4 pmol mg-1 protein (P < 0.01). In the presence of L-NOARG, there was a significant decrease in cyclic GMP content to control. However, there was no increase in cyclic GMP content in response to EFS. Levels of cyclic AMP remained unchanged following EFS. 5. Treatment with the N-type VOCC-inhibitor, omega-conotoxin GVIA (0.1 microM) reduced NO-dependent relaxations, the effect being most pronounced at low frequencies (1-4 Hz) of stimulation. The NO independent second phase of the relaxation, studied in the presence of L-NOARG (0.3 mM) at 16-30 Hz, was however markedly reduced or abolished by omega-conotoxin GVIA. omega-Conotoxin MVIIC (1 microM)or omega-agatoxin IVA (30 nM) had no effect on electrically evoked relaxations.6. These results suggest that NANC-nerve derived urethral relaxation in the pig consists of two apparently independent components. One is mediated by NO and associated with an increase in cyclic GMP content. The other mediator is unknown and produces relaxations not associated with changes in levels of cyclic nucleotides. The release of this mediator seems to involve the N-type VOCC, since the relaxation was markedly reduced or abolished by omega-conotoxin GVIA.

Animals↗
PubMed1995

Possible contribution of long open state to noninactivating Ca2+ current in detrusor cells.

The whole cell patch-clamp technique was used to measure Ca2+ current in isolated smooth muscle cells from guinea pig urinary bladder. Noniactivating Ca2+ channel current was modeled incorporating the long open state of the Ca2+ channel. When inactivation was examined over a wide voltage range, a completely U-shaped curve was obtained. Lack of inactivation at +80 mV could be attributed to the long open state induced by large depolarization as well as to minimal Ca2+ influx and Ca(2+)-dependent inactivation. Activation parameters were obtained by comparing the amplitudes of conditioned (by +80 mV, 5 s) and unconditioned test potentials. With the use of the activation curve and the U-shaped inactivation curve, a noninactivating current that peaks around +20 mV was obtained. This current is composed of a so-called "window" current and a persistent current brought about by the long open state. Differences in the voltage dependence of the development of the long open state in various smooth muscles, as well as differences in the equilibrium constant between open and inactivated states, could underlie the different patterns of contractile behavior that characterize smooth muscles.

Animals↗
PubMed1995

Physiological and morphometric studies into the pathophysiology of detrusor hyperreflexia in neuropathic patients.

The in vitro responses of isolated detrusor strips obtained from neuropathic patients with neuropathic bladder dysfunction were found to be supersensitive to both carbachol [ED50 1.2 x 10(-6) M. versus 2.5 x 10(-6) M. in control strips; p < 0.005] and potassium chloride [ED50 41.8 mM. versus 49.3 mM. in control strips, p < 0.05]. There were no significant differences in the frequency-response curves obtained with intramural nerve stimulation. However, expressed as a percentage of the maximal response with carbachol, the maximal responses to intramural nerve stimulation in neuropathic strips were reduced [58.3 +/- 21% versus 74.4 +/- 18% for control strips; p < 0.005, Student t test]. Morphometric studies revealed a lower density of 'presumptive' cholinergic nerves in neuropathic detrusor (1.0 +/- 1.4 x 10(-4) microns -2 compared with 3.2 +/- 1.3 x 10(-4) microns -2 in controls, p < 0.05, Mann Whitney U test). The combined physiological and morphometric results were in keeping with a state of postjunctional supersensitivity of neuropathic detrusor secondary to a partial parasympathetic denervation of the smooth muscle. This may be an important factor in the etiology of detrusor hyperreflexia. The contractility of neuropathic tissue in response to field stimulation was found to be much lower than normal (2.4 +/- 1.5 g./10 mg. versus 5.9 +/- 3.0 g./10 mg., p < 0.001; Mann Whitney U test). This reduced contractility to neuronal stimulation might be responsible for some of the characteristics of bladder dysfunction that are seen in patients with similar neurological conditions.

Adult↗
PubMed1994

Distribution of nitric oxide synthase containing neurons in the rectal myenteric plexus and anal canal. Morphologic evidence that nitric oxide mediates the rectoanal inhibitory reflex.

PURPOSE: Following the demonstration that a novel neurotransmitter, nitric oxide (NO), is released during neurogenic relaxation of the internal anal sphincter in vitro, it has been suggested that NO could mediate the rectoanal inhibitory reflex in vivo. The aim of this study was to establish whether the distribution of NO-producing nerves in the anorectum is consistent with this proposed role. METHODS: NO is synthesized in neurons which contain the enzyme nitric oxide synthase and their presence in the anorectum was determined in tissue obtained from nine abdominoperineal and three anterior resection specimens in patients undergoing surgery for rectal carcinoma. Cryostat sections were stained for nitric oxide synthase immunoreactivity, pan-neuronal/axonal immunoreactivity, and NADPH diaphorase activity. RESULTS: Nitric oxide synthase immunoreactivity is present in a subpopulation of neurons in rectal myenteric ganglia which also contain NADPH diaphorase activity. Use of the latter histochemical technique enabled the structure and distribution of nitric oxide synthase containing neurons to be determined in whole-mount preparations. Individual neurons have Dogiel type 1 morphology and are present throughout the rectal myenteric plexus. In the distal rectum, positively stained axons enter shunt fascicles which descend into the anal canal, where they ramify into and throughout the internal anal sphincter. Within the sphincter, positively stained nerves lie in close proximity to smooth muscle cells. CONCLUSION: These results are consistent with the hypothesis that NO is the neurotransmitter that mediates the rectoanal inhibitory reflex.

Adult↗
PubMed1994

Abnormalities of nitric-oxide-producing neurons in Hirschsprung's disease: morphology and implications.

Nitric oxide (NO) is a recently discovered neurotransmitter that is thought to mediate relaxation of gut smooth muscle during peristalsis. To assess its role in the pathophysiology of Hirschsprung's disease, the authors examined the distribution of neurons that produce NO in specimens from seven infants with this condition. Immunohistochemical analysis of cryostat sections for nitric oxide synthase (NOS) immunoreactivity (NOS catalyzes the production of NO) showed that NOS is localized in a substantial subpopulation of enteric neurons in both the myenteric and submucosal plexuses in the ganglionated gut, but it was completely absent in aganglionic bowel. NOS immunoreactivity specifically colocalizes in neurons that also contain NADPH-diaphorase activity. This finding enabled the distribution of NO-producing neurons to be determined using whole-mount histochemistry, a technique that allows the enteric neural network to be examined intact. In normal bowel, NO-producing neurons are arranged in star-shaped myenteric and submucosal ganglia, which are joined to one another by nerve fibers to form a meshwork of variable geometry. Individual neurons exhibit Dogiel type 1 morphology. Axonal processes leave the myenteric plexuses and lie parallel to muscle bundles in both muscle layers of the gut. In the transition zone, ganglia are initially present, but their orientation changes so that both they and the internodal strands that connect them are aligned linearly along the craniocaudal axis of the gut tube. More distal still, ganglia and then all NOS activity disappear completely. These results suggest that in Hirschsprung's disease, the failure of aganglionic bowel to relax during peristalsis might be caused by the absence of NO-producing neurons.

Amino Acid Oxidoreductases↗
PubMed1994

An assessment of the contribution of visco-elastic factors in the aetiology of poor compliance in the human neuropathic bladder.

OBJECTIVE: To compare the mechanical properties of fullthickness bladder strips from poorly compliant neuropathic bladders with controls and to determine the overall contribution that mechanical factors might have in the aetiology of the poor compliance of medium-fill cystometry. PATIENTS AND METHODS: The visco-elastic properties of full-thickness bladder strips from 11 neuropathic patients (with poorly compliant bladders during medium-fill cystometry) were compared with strips from 11 control bladders. A strip (measuring 2 cm long and 0.5 cm wide) was mounted in an organ bath and stretched by 1 cm at a slow and at a fast rate. The stretches were repeated in modified Krebs solution containing zero calcium and 12 mM magnesium. The final experiment involved stretching the strip by 1 cm in < 1 s (instantaneous stretch). RESULTS: Only modest differences in the peak tensions of both tissues were uncovered by the slow and fast stretches (fast stretch: 14.6 +/- 5.5 in neuropaths vs 10.1 +/- 4.1 g in controls, P = NS; slow stretch: 9.6 +/- 3.5 in neuropaths vs 6.7 +/- 2.5 g in controls, P < 0.05). Stretches carried out in modified Krebs solution resulted in lower tensions. Fast, intermediate and slow components of viscous decay (derived from the rate of tension decay following the instantaneous stretch) were not significantly different in neuropaths compared to controls (P = NS). CONCLUSION: The differences in the mechanical properties between neuropathic and control bladder strips were small and could not alone have accounted for the large differences in bladder compliance that was observed between neuropathic and normal patients during medium-fill cystometry. This implied that neurogenic rather than mechanical factors were more important in the aetiology of the observed poor compliance in these patients.

Adolescent↗
PubMed1993

Regulation of tone in pig urethral smooth muscle.

Cystometry and urethral pressure profilometry performed in Large White pigs reveal a fall in urethral pressure before micturition. The area of highest pressure in the female is in the mid-urethra. Circular smooth muscle dissected from this region generates a high spontaneous tone, which is increased by phenylephrine and carbachol, but is unaffected by guanethidine and atropine. Electrical field stimulation using different parameters produces frequency-dependent relaxations or a combination of relaxation and contraction, all sensitive to tetrodotoxin. Only the contraction is inhibited by atropine and guanethidine. However, phasic relaxations are abolished by N-nitro-L-arginine, an effect partially reversed by L- but not by D-arginine. Oxyhemoglobin also marginally reduces the relaxations. Sodium nitroprusside produces concentration-dependent relaxations of the urethral smooth muscle, maximal at 10(-5) M. It is suggested that the urethral muscle generates a high myogenic tone that maintains continence and can be enhanced by adrenergic and cholinergic input, or inhibited by NANC innervation, partially mediated by the transmitter nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1993

Experimental model of bladder outflow tract obstruction in the guinea-pig.

Bladder outflow tract obstruction was produced in immature female guinea-pigs. Obstruction caused an increase in voiding pressure and bladder weight and a decrease in bladder compliance. No change occurred in the sensitivity of obstructed detrusor strips to exogenous agonists, but the force of contraction and response to electrical stimulation of the intrinsic nerves were less than in the strips from controls. The response of strips from sham-operated animals to exogenous agonists and to electrical stimulation was greater than that from obstructed animals. The effects of length and tension could not account for the in vitro responses from obstructed animals. Histology after obstruction showed muscle hypertrophy, connective tissue infiltration and decrease in nerve density. Many of the changes resembled those seen in the obstructed human bladder.

Adenosine Triphosphate↗
PubMed1993

Effects of cromakalim on the electrical slow wave in the circular muscle of guinea-pig gastric antrum.

1. In circular muscle strips of the antrum of guinea-pig stomach, the effects of cromakalim were studied on mechanical activity and intracellular membrane potential. 2. Cromakalim inhibited mechanical activity at concentrations higher than 1 microM, accompanied by membrane hyperpolarization and a decrease in membrane resistance. The hyperpolarization was markedly potentiated in K(+)-free solution and was still observed in the absence of Na+. 3. Slow wave electrical activity was relatively resistant to cromakalim. Changes in its amplitude and frequency were not consistent but blockade of slow waves was never observed. In many preparations cromakalim induced spike-like potentials at the top of slow waves, or when spike-like potentials already existed they were potentiated. However, mechanical activity was always inhibited. 4. Inhibition by cromakalim of the phasic contractions associated with the slow waves, could not be reversed by increasing the external K+ concentration (12-30 mM). 5. The results suggest that in guinea-pig stomach muscle mechanical suppression by cromakalim does not simply result from membrane hyperpolarization or from inhibition of slow waves. A clear dissociation was found between the mechanical and electrical activities. Slow waves, particularly their frequency, are relatively insensitive to membrane hyperpolarization.

Animals↗
PubMed1993

Evidence for multiple open states of the Ca2+ channels in smooth muscle cells isolated from the guinea-pig detrusor.

1. Whole-cell voltage clamp techniques were used to examine the properties of voltage-dependent Ca2+ channel currents in single smooth muscle cells enzymatically dissociated from guinea-pig urinary bladder. Potassium currents were blocked with intracellular Cs+. A holding potential of -60 mV was normally applied. 2. When the membrane potential was returned to the holding potential after a depolarizing step, tail currents were seen after depolarizations to positive potentials, and the size of the tail current increased with increasing positivity of the preceding depolarization. 3. After depolarization to +80 mV (a potential at which little inward current flowed through the Ca2+ channels) tail currents on returning to the holding potential increased in size as the duration of the depolarization was increased. 4. Investigation of the mechanism mediating the tail currents showed that they were not flowing through non-selective cation channels, and had no contribution from Ca(2+)-activated Cl- channels or Na(+)-Ca2+ exchange. 5. The tail currents and the inward currents evoked by a simple depolarizing test potential were equally decreased by nifedipine in a dose-dependent manner. This suggests that L-type Ca2+ channels are responsible for both of the two types of inward currents. The inward currents were also inhibited in a similar manner when caffeine was applied. 6. Although the tail currents evoked on stepping from +80 mV to a holding potential of -60 mV increased in size with the duration of the conditioning potential, the total membrane Ca2+ conductance did not increase, since the inward currents evoked on stepping to +20 mV (a potential at which the Ca2+ channels are still fully activated) did not change with time. 7. The amplitude of the inward current evoked by a simple depolarizing test potential was similar to that evoked on stepping to the same test potential after preconditioning at +80 mV, if the test potential was higher than +20 mV. However, following repolarization to the holding potential, the amplitude of the subsequent tail current was larger and the deactivation time constant longer, after the conditioning depolarization. These results suggest that the voltage-dependent Ca2+ channels have at least two open states with different time constants, the tail current being the result of a long open channel state induced by large depolarizations. 8. When variable repolarizing potentials were applied after n +80 mV depolarization (5 s), the current-voltage relationship of the tail current was nearly linear between -60 and +30 mV. The deactivation was faster when a larger repolarization step was applied.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗