Analysis of contractions induced by transmural stimulation in the isolated sphincter of Oddi

Exogenous purines induce differential responses in the proximal and distal regions of the possum sphincter of Oddi

1. The aim of this study was to compare the effect of exogenous ATP and adenosine on spontaneous motility of the proximal and distal regions of the possum sphincter of Oddi (SO). 2. ATP or adenosine (1 microm-1 mm) was applied to distal-SO or proximal-SO muscle rings in organ baths in the absence or presence of tetrodotoxin (TTX) or P1/P2 antagonists. 3. Both ATP and adenosine altered spontaneous activity, predominantly in proximal-SO rings. 4. Exogenous ATP induced a bi-phasic response consisting of a brief TTX-sensitive excitatory component, and a longer-lasting TTX-insensitive inhibitory component. 5. The excitatory ATP response likely involves P2X receptors, whereas the late inhibitory response likely involves P2Y receptors. 6. Exogenous adenosine decreased spontaneous SO activity, via a TTX-insensitive mechanism. 7. Exogenous purines modulate SO motility, acting primarily in the proximal region of the SO, via neural and non-neural mechanisms and multiple purine receptor subtypes.

Exogenous adenosine triphosphate and adenosine stimulate proximal sphincter of oddi motility via neural mechanisms in the anesthetized Australian possum

We aimed to determine if exogenous adenosine triphosphate or adenosine modulated sphincter of Oddi motility and involved neural mechanisms. Sphincter of Oddi motility was recorded in anesthetized possums by manometry. Adenosine triphosphate or adenosine (1 microM-10 mM) was applied topically to the sphincter before and after pretreatment with tetrodotoxin, hexamethonium, atropine, or Nomega-nitro-L-arginine methyl ester. Sphincter contraction amplitude and frequency were quantified. Adenosine triphosphate induced a concentration-dependent increase in proximal sphincter contraction amplitude and frequency (P < 0.05). This response was reduced by tetrodotoxin and atropine but enhanced by hexamethonium and Nomega-nitro-L-arginine methyl ester. Adenosine concentration dependently increased proximal sphincter contraction amplitude (P < 0.05) only. This response was reduced by tetrodotoxin, atropine, and Nomega-nitro-L-arginine methyl ester, whereas hexamethonium had no effect. We conclude that exogenous adenosine triphosphate and adenosine stimulate proximal sphincter of Oddi motility via neural mechanisms, involving cholinergic motor neurons. Adenosine triphosphate may further modulate sphincter motility via nicotinic and nitrergic pathways.

Identification of the cholinergic neurons in guinea-pig sphincter of Oddi ganglia

The muscular tone of the sphincter of Oddi (SO) can be up- or down-regulated by neurons that lie within ganglia in the wall of the tissue. Previous studies have demonstrated that neurons in the ganglia of the guinea-pig SO can be classified into two major populations, one of which expresses tachykinins and enkephalin and another which expresses nitric oxide synthase. Although results of previous pharmacological studies indicate that acetylcholine is released in the SO, the neurons that express this neurotransmitter have not previously been identified. This study was conducted to establish which neurons in the ganglia of the guinea-pig SO are cholinergic by examining the distribution of choline acetyltransferase (ChAT) immunoreactivity, since the enzyme, ChAT is necessary for acetylcholine synthesis. Choline acetyltransferase immunoreactivity was intense and widespread in the ganglionated plexus of the SO. ChAT-immunoreactive nerve fibers were present in ganglia, interganglionic fiber bundles and in the circular muscle layer. Neurons that were immunoreactive for ChAT comprised about 69% of the population and most of these neurons were also tachykinin-immunoreactive. Co-expression of ChAT and nitric oxide synthase was not observed in nerve cell bodies or nerve fibers. Data from this study support the concept that SO ganglia are largely made up of two populations of neurons, one excitatory and the other inhibitory, on the basis of their chemical coding. The excitatory neurons are cholinergic and co-express tachykinin and opiate peptides and the inhibitory neurons are ChAT-negative and express nitric oxide synthase.

Immunohistochemical identification of neurons in ganglia of the guinea pig sphincter of Oddi

The sphincter of Oddi is a smooth muscle sphincter that regulates the flow of bile into the duodenum. To identify potential chemical coding in sphincter of Oddi neurons, immunohistochemistry and histochemistry were employed to assay for putative neurotransmitters and related synthetic enzymes in wholemount preparations, with and without colchicine treatment. Immunoreactivities for enkephalin-endorphin (ENK-END), substance P (SP), nitric oxide synthase, vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), and calcitonin gene-related peptide (CGRP) were demonstrated within the ganglionated plexus. Roughly half of the neurons in the sphincter of Oddi expressed immunoreactivity for both SP and ENK-END, but not for nitric oxide synthase. About 25% of the neurons expressed nitric oxide synthase immunoreactivity as well as NADPH-diaphorase activity. This contingent of neurons was made up of two subgroups: one that expressed immunoreactivity for VIP, the other for NPY. Neurons that expressed CGRP immunoreactivity were sparse in sphincter of Oddi ganglia; however, many axons immunoreactive for both CGRP and SP were present in the ganglionated plexus. The CGRP/SP fibers are probably visceral afferents that may influence ganglionic output through axon reflex circuits. These results, along with studies of the actions of these neuroactive compounds on sphincter tone, support the view that ganglia of the sphincter of Oddi are largely comprised of excitatory (SP/ENK-END-immunoreactive) and inhibitory (nitric oxide synthase/VIP- or NPY-immunoreactive) neurons, and that sphincter of Oddi tone is controlled by the regulation of the outputs of these two groups of cells.

Regional differences in nitric oxide-mediated relaxation of the rabbit sphincter of Oddi

We studied the role of the L-arginine-nitric oxide (NO) pathway in non-adrenergic, non-cholinergic (NANC) relaxation of the rabbit sphincter of Oddi by recording changes in isometric tension in response to electrical field stimulation in two series of experiments. In a first set of experiments, biliary sphincters of Oddi removed from New Zealand white rabbits were placed horizontally in an organ bath containing oxygenized, buffered (pH 7.4) Krebs solution. Contractile responses of the whole sphincter to field stimulation were determined. In the second set of experiments, sphincter of Oddi was divided into two parts and the effects of field stimulation were studied separately on areas close to the duodenal papilla (area I) and areas close to the common bile duct (area II). In the whole sphincter of Oddi, field stimulation induced an initial twitch-like contraction followed by relaxation proportional to the number of stimuli (3 and 10 stimuli at 20 Hz, 50 V, 0.1 ms). The magnitude of the contractile responses was considerably reduced by 1 microM atropine, phentolamine and oxprenolol (NANC solution). Field stimulation produced dose-dependent contractions of both segments of sphincter of Oddi in response to the same protocol as used with whole sphincter of Oddi. However, preincubation with NANC solution produced monophasic relaxations in response to field stimulation in area I, whereas area II preparations such as the whole sphincter of Oddi responded with contractions followed by minimal relaxations. Field stimulation failed to induce either contractions or relaxations in the presence of 1 microM tetrodotoxin.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitric oxide mediates nonadrenergic, noncholinergic neural relaxation in the Australian possum

BACKGROUND

Nitric oxide has been shown to play an important role in neurally mediated relaxations of gastrointestinal smooth muscle. The aim of this study was to determine whether NO may be the inhibitory transmitter to circular smooth muscle from the sphincter of Oddi of the Australian brush-tailed possum (Trichosurus vulpecula).

METHODS

The effects of drugs on relaxations evoked by electrical-field stimulation of circular muscle strips precontracted with either erythromycin or carbachol were studied. Preparations were also processed histochemically to determine the presence of nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase reactivity in the tissue.

RESULTS

NG-nitro-L-arginine methyl ester reduced the amplitude of relaxations; this effect could be partially reversed by millimolar concentrations of L-arginine but not by D-arginine. Oxyhemoglobin also reduced the amplitude of the relaxations, and sodium nitroprusside mimicked the relaxations in precontracted strips. Histochemical processing revealed the presence of nerve cell bodies and nerve fibers associated with the circular muscle layer, which are reactive for NADPH-diaphorase and are thus likely to contain NO synthase.

CONCLUSIONS

These results are all consistent with NO released from nerve cells mediating a significant part of the nonadrenergic, noncholinergic relaxation of the circular muscle layer of the sphincter of Oddi.

Innervation of the sphincter of Oddi: physiology and considerations of pharmacological intervention in biliary dyskinesia

The sphincter of Oddi is a small sphincter which is strategically placed at the junction of the bile duct and pancreatic duct with the duodenum. It regulates the flow of bile and pancreatic juice into the duodenum and prevents reflux of duodenal contents into the ducts. The structure of the sphincter of Oddi differs from species to species and consequently its physiological action varies in different species. Anatomical and immunohistochemical investigations have demonstrated that the sphincter of Oddi is richly innervated by cholinergic, adrenergic and peptidergic neurons. In addition, neural connections exist between the sphincter, gallbladder and proximal gastrointestinal tract. These nerves in addition to hormones are important in the control of sphincter of Oddi motility and function. The normal human sphincter of Oddi is characterized by prominent phasic contractions which are superimposed on a modest basal pressure. These contractions are present throughout the interdigestive period. The contractions and basal pressure are inhibited by ingestion of a meal or infusion of cholecystokinin octapeptide, thus enhancing the flow of bile and pancreatic juice into the duodenum. Sphincter of Oddi dysfunction has been described in patients who present with recurrent biliary type pain and no evidence of a structural cause for the pain. Motility disorders characterized as an elevated basal pressure, rapid contraction frequency, paradoxical response to cholecystokinin octapeptide or excess of retrograde contractions have been identified. A number of pharmacologically active substances have been used in an attempt to treat these patients. Such pharmaceuticals include nitrites, Ca2+ channel blockers and smooth muscle relaxants. Their effect is transient and side effects relating to cardiovascular actions preclude their longterm use. Division of the sphincter either endoscopically or by open operation has been demonstrated by prospective clinical trials to be the most efficacious treatment for patients with a stenosed sphincter manometrically demonstrated by a high basal pressure. Improved understanding of the controlling mechanisms of sphincter of Oddi motility and the pathophysiology of sphincter of Oddi dysfunction should assist in the development of effective pharmacotherapy for these disorders.

Nerve-mediated contractile and electrical activity of the guinea-pig choledocho-duodenal junction

The intrinsic motor innervation of the guinea-pig choledocho-duodenal junction was investigated by recording the contractile and intracellular electrical activity of smooth muscle from different regions of this tissue. Electrical transmural nerve stimulation evoked phasic contractions in rings of muscle from the ampulla (0.45 s-1) and tonic contractions in rings of muscle from the choledochal sphincter. Intracellular microelectrode recordings from muscle strips from these two regions revealed that excitatory junction potentials (peak amplitude 7 mV) evoked by transmural nerve stimulation were more conspicuous in muscle strips from the choledochal sphincter, but inhibitory junction potentials (peak amplitude 13 mV) were of larger amplitude in muscle strips from the ampulla. Contractions and membrane depolarization evoked by transmural nerve stimulation were sensitive to 1.4 microM atropine and abolished by 3.1 microM tetrodotoxin. Histological studies on the choledocho-duodenal junction also revealed that the distribution of smooth muscle was non-uniform along the tissue. These results suggest that the two regions may have different functions in the motility of the choledocho-duodenal junction.