Stimulus-response function studies of esophageal mechanosensitive nociceptors in sympathetic afferents of opossum

1. Single-unit activity was recorded from afferent fibers in either the paravertebral sympathetic chain or the splanchnic nerves. Forty-three fibers that responded to distension of the smooth-muscle portion of esophagus were selected for further study. 2. Out of the 43 fibers, 27 (62%) had ongoing resting activity, and 16 (38%) were silent. The mean resting activity of these fibers was 0.28 +/- 0.06 imp/s (range, 0-2.6 imp/s). 3. Repeated distensions of the esophagus to a fixed pressure (80 mmHg) evoked spike discharge at a reproducible rate. There was no evidence of facilitation or inhibition of subsequent responses. The mean coefficient of variation (CV) was 0.17 +/- 0.05 imp/s (n = 5). 4. The stimulus-response function (SRF) to intraluminal graded distension was studied in 35 fibers. Thirty-three fibers showed linear increase in firing that did not saturate up to 120 mmHg. Two fibers reached maximal discharge rate at 60 mmHg. The mean discharge rate at 120 mmHg pressure was 14.87 +/- 1.52 imp/s. 5. Threshold pressure for activation of each fiber was calculated by a least-squares linear-regression plot of the SRF. The threshold pressure varied from 0 to 50 mmHg (mean, 16.21 +/- 2.86 mmHg). The distribution profile of the threshold values showed that there were two separate populations of mechanosensitive receptors: 1) wide-dynamic-range mechanonociceptors (WDR-MN) with mean threshold pressure of 2.89 +/- 0.75 mmHg (range, 0-7 mmHg; n = 22); and 2) high-threshold mechanonociceptors (HT-MN) with mean threshold of 33.26 +/- 2.52 mmHg (range, 19-50 mmHg; n = 13). 6. Discharge evoked by esophageal peristalsis was studied in five WDR-MN and five HT-MN units. Whereas all five WDR-MN units (threshold value, 2.6 +/- 0.96 mmHg) responded to peristalsis, none of the HT-MN units (threshold value, 31.2 +/- 4.01 mmHg) did so. The mean response to peristaltic contraction in WDR-MN units was 5.32 +/- 1.36 imp/s, which was 24.7% of the maximal response (21.53 +/- 1.92 imp/s; n = 5) at 120 mmHg. The duration of evoked response to peristaltic contraction was 10-12 s. 7. The activity profile of the units to 60-s balloon distension at near threshold and higher pressures showed three patterns: 1) rapid adaptation, 2) slow adaptation, and 3) slow adaptation with after discharge. The rapidly adapting fibers became slowly adapting with greater degrees of esophageal distension. The units that showed rapid or slow adaptation at low-distension pressure became indistinguishable from one another at high-distension pressure.(ABSTRACT TRUNCATED AT 400 WORDS)

Synthesis and pharmacological study of antihyperlipaemic activity of 2-substituted thieno(2,3-d)pyrimidin-4(3H)-ones

A series of 2-substituted thieno(2,3-d)pyrimidin-4-(3H) ones (1-15) was prepared by the reaction of thiophene ortho-aminoester (IV) with a variety of nitriles (V) under acidic conditions, and screened for antihyperlipaemic activity in various animal models. While most of these compounds were found active, 2-chloromethyl-5,6,7,8-tetrahydrobenzo(b)thieno(2,3-d) pyrimidin-4(3H)-one (5) was found to be the most active of all. The serum triglyceride lowering activity exhibited by 5 was found comparable to that of clofibrate and riboflavin tetrabutyrate. Compound 5 was also found to be safe as indicated by acute and chronic toxicity studies in mice and rats.

Mucosal peptidergic innervation of the opossum esophagus and anal canal: a comparison with snout skin

Nerves within and under the esophageal epithelium of the opossum esophagus were investigated morphologically with osmication and immunohistochemically for ten neuropeptides. The structurally similar but functionally diverse epithelia of the anal canal and snout skin, on which no immunohistochemical information exists, were similarly investigated for comparison. Total innervation was estimated from osmication, which revealed intraepithelial nerves in all three tissues in the following order of density: snout skin greater than anal canal greater than esophagus. Calcitonin gene-related peptide and substance P occurred in all three organs. The snout skin had intraepithelial galanin nerves but not vasoactive intestinal polypeptide, while conversely the esophagus and anal canal had vasoactive intestinal polypeptide but not galanin. All peptides found intraepithelially also occurred subepithelially. Calcitonin gene-related peptide, galanin, neuropeptide Y, substance P and vasoactive intestinal polypeptide subepithelial nerves occurred in all the tissues, while gastrin releasing peptide nerves occurred infrequently in the subepithelial regions of the esophagus and anal canal, but not the snout skin. As these epithelia neither secrete nor absorb, their nerves are presumably sensory. The peptides investigated could not account for all intraepithelial nerves demonstrated by osmium. Differences in the innervation of these epithelia may result from their differing sensory requirements.

Effect of bradykinin on opossum esophageal longitudinal smooth muscle: evidence for novel bradykinin receptors

Bradykinin (BK) produced a concentration-dependent contraction of the longitudinal but not the circular muscle of the opossum esophagus. The pD2 value of BK on the longitudinal muscle was 6.58 +/- 0.06 M. The maximal response of the longitudinal muscle to BK was 44% compared to carbachol. The putative B1 agonist des-Arg9-BK produced contraction of longitudinal muscle but the putative B1 receptor antagonist des-Arg9-[Leu8]-BK (20 and 50 microM) did not modify the responses to BK or des-Arg9-BK. The putative B2 antagonists d-Phe7-BK, Thi5,8-d-Phe7-BK and d-Arg0-Hyp3-Thi5,8-d-Phe7-BK (B6572) were found to be agonists in this tissue. The rank order of potency with respect to Emax obtained from cumulative concentration-response curves was BK greater than Thi5,8-d-Phe7-BK greater than B6572 greater than d-Phe7-BK and pD2 values of these compounds were 6.58 +/- 0.06, 6.30 +/- 0.28, 6.74 +/- 0.08 and 5.05 +/- 0.04 M, respectively. The excitatory effect of BK and Thi5,8-d-Phe7-BK was not modified by tetrodotoxin (1 and 10 microM), atropine (1 microM) or indomethacin (1 and 10 microM), but was significantly (P less than .001) inhibited by nifedipine (1 and 10 microM). Three putative "tissue selective" BK antagonists, d-Phe2,7-BK (B4404), d-Phe7-Hyp8-BK and Phe2-d-Phe7-BK also had an agonistic effect on longitudinal muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Serum nickle estimation in acute myocardial infarction

Serum nickle was estimated by atomic absorption spectrometer in 20 healthy controls and in 25 cases of acute myocardial infarction at 12 hourly intervals upto 48 hours, after the onset of chest pain. The mean serum nickel was 0.27 micrograms/dl in healthy controls and 0.40,050,049 and 0.30 micrograms/dl in patients of acute myocardial infarction. The serum nickel values were significantly (P less than 0.001) raised upto 36 hours in acute myocardial infarction when compared with controls.

Effect of cold temperature on membrane potential responses in opossum esophageal circular muscle

The effects of cold temperature on resting membrane potential (RMP) and membrane potential responses to depolarizing electrical current and intramural nerve stimulation were examined in opossum esophageal circular smooth muscle. Intracellular recordings were made in smooth muscle strips obtained from 7 to 8 cm (proximal site) and 1 to 2 cm (distal site) above the lower esophageal sphincter. RMP was not affected by changes in temperature between 34 and 22 degrees C. Cooling caused progressive inhibition of the amplitude and a slight increase in the duration of the spike potential produced by depolarizing current. Cooling did not modify the threshold for spike potential generation but decreased the spike amplitude from 34.0 +/- 0.5 mV at 34 degrees C to 14.1 +/- 2.2 mV at 22 degrees C (P less than 0.01). Electrical field stimulation with single electrical pulses (1.0 ms) produced tetrodotoxin-sensitive biphasic membrane responses consisting of initial hyperpolarization, or an inhibitory junction potential followed by depolarization that increased in amplitude as temperature was decreased from 34 to 26 degrees C and then decreased in amplitude as temperature was further decreased. At both proximal and distal sites cooling from 34 to 22 degrees C caused more than a twofold increase in the duration of hyperpolarization and time to peak depolarization. However, the increase in the absolute time of the duration of hyperpolarization and the time to peak depolarization was significantly greater at the distal than proximal esophageal site. Cooling to 16 degrees C decreased RMP and nearly abolished the biphasic membrane potential response.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of vagal esophageal tension-sensitive afferent fibers in the opossum

1. Single-unit vagal afferent activity was recorded from 35 fibers that demonstrated evoked response to distension in the smooth muscle portion of the esophagus in anesthetized opossums. 2. The conduction velocities, measured in 22 fibers, varied from 1.0 to 21.33 m/s. Eight fibers (36%) had conduction velocities in the range of C-fibers (less than 2.5 m/s), whereas 14 (64%) had velocities in the range of A delta-fibers (3.16-21.33 m/s). All fibers were spontaneously active with an average discharge rate of 7.3 +/- 1.0 imp/s (mean +/- SE; range, 1.2-23 imp/s). 3. Esophageal distension produced a reproducible increase in discharge rate that adapted slowly to sustained distension. The average threshold pressure of the endings was 10 mmHg. The saturation pressure was 70 mmHg with cumulative, stepwise distension and 56 mmHg with graded, discrete distensions, respectively. 4. The discharge rate at the saturation pressure was 46 +/- 7 imp/s with cumulative, stepwise distensions and was 59 +/- 4 imp/s with graded, discrete distensions. The difference in maximum discharge between these two modes of distension was not statistically significant (P greater than 0.05). 5. Esophageal peristaltic contraction was associated with bursts of spike discharge with an average rate of 53.6 +/- 4.7 imp/s. 6. Two types of fibers were identified based on their duration of spike discharge associated with peristaltic contraction. The short-activity fibers showed a short duration of response consisting of approximately 3 s of spike bursts in response to swallows. These short-activity fibers were not activated by either stretch or contraction of the longitudinal esophageal muscle. The long-activity fibers showed a long duration of response consisting of approximately 10 s of activity in response to swallows. These long-activity fibers could be activated by longitudinal muscle stretch or contraction. 7. It is concluded that esophageal tension-sensitive mechano-receptors associated with vagal afferents are activated by physiological peristalsis and are present "in series" with either circular or longitudinal muscle layers.

Esophageal responses to transient and sustained esophageal distension

With the use of intraluminal manometry in alpha-chloralose-anesthetized opossums, distal esophageal and lower esophageal sphincter responses to prolonged midesophageal balloon distension were compared with those evoked by single transient distensions, vagal efferent stimulation, and swallowing. Balloon inflation caused sphincteric relaxation that recovered during small volume but persisted during large volume-prolonged distension. The esophageal body was either quiescent or exhibited nonperistaltic contractions during prolonged distension. Balloon deflation induced non-peristaltic esophageal and sphincteric contractions as well as further sphincter relaxation. Responses to prolonged large and small volume balloon distension resembled those evoked by high- and low-frequency vagal efferent stimulation, respectively. However, vagal-stimulated "on" contractions were not seen with balloon distension, and atropine did not modify excitatory responses occurring during or after prolonged distension. Although transient distension induced peristaltic esophageal contractions, the peristaltic velocity was faster than swallow-induced peristalsis. With transient distension, atropine prolonged the latency to contraction in the mid but not the distal smooth muscle segment and thus increased peristaltic velocity. These studies demonstrate that 1) esophageal distension evokes a wide spectrum of lower esophageal sphincter and esophageal body response, and 2) cholinergic neurons play a minimal role in distension-induced responses of the distal esophageal circular muscle below the distending balloon.

Inhibitory effect of calcitonin gene-related peptide and calcitonin on opossum esophageal smooth muscle

Calcitonin gene-related peptide (CGRP) is widely distributed in the gastrointestinal nerves, including those of the esophagus. The present investigation was undertaken to examine the effect and the mechanism of action of CGRP on the lower esophageal sphincter and esophageal contractions. This peptide caused dose-dependent relaxation of the lower esophageal sphincter. The D50 for inhibitory effect of intraarterial CGRP on the sphincter was 5.0 X 10(-13) mol/kg. Calcitonin gene-related peptide is 3000 times more potent than calcitonin. The effect of CGRP on the lower esophageal sphincter was partially antagonized by tetrodotoxin or black widow spider venom. The inhibitory effect of CGRP on the sphincter appears to be exerted at two levels: (a) at the sphincteric smooth muscle, and (b) at the noncholinergic, nonadrenergic inhibitory neurons. Calcitonin gene-related peptide also exerts a potent inhibitory effect on the peristaltic contraction of the esophageal body in response to swallowing and vagal efferent stimulation. Using immunohistochemical studies we also showed the presence of CGRP-immunoreactive neurons within the myenteric ganglia of the esophagus. These studies suggest that CGRP may play an important role as an inhibitory neurotransmitter in the esophagus.

Localization of galanin immunoreactivity in the opossum esophagus

Galanin-like immunoreactivity was studied at 7 levels of the opossum esophagus, lower esophageal sphincter (LES) and adjacent portion of the stomach by indirect immunofluorescence; it was restricted to nervous structures. The majority of myenteric and submucous neurons were galanin-positive and received positive axo-somatic terminations. They also sent out axons staining positively. Galanin-positive fibers and a few atypically located neurons formed a mucous plexus at the bases of mucous glands. Varicose galanin fibers innervated the muscularis mucosae, circular and longitudinal muscle layers, while thick fascicles traversed the muscularis mucosae and circular muscle, possibly interconnecting the myenteric, submucous and mucous plexuses. Galanin-positive fibers did not supply blood vessels. There was no obvious gradient of innervation density along the esophagus, but the sphincter appeared to be more densely innervated than the esophageal body. There was no galanin-positive input to striated muscle. In view of its widespread distribution, this neuropeptide may serve multiple functions in the esophagus.

Identification, localization and classification of muscarinic receptor subtypes in the gut

Muscarinic receptors in the gastrointestinal tract are present on enteric neurons, presynaptic and prejunctional axonal endings, intramural endocrine cells as well as directly on effector cells such as smooth muscle and glandular and epithelial cells. Neural M1 stimulatory receptors are present on myenteric and submucous neurons, while neural M2 inhibitory receptors are present on their axonal endings. Muscle M2 and glandular M2 receptors are stimulatory. Functional and ligand binding studies show that there is heterogeneity among different muscarinic receptors in the gastrointestinal tract. The neural M1 muscle M2 and glandular M2 receptors are distinct from each other, but presynaptic and prejunctional M2 receptors appear to be similar to muscle M2 receptors. The relationship of the gut muscarinic receptors to the structurally-defined muscarinic receptors in the brain is unclear. However, they appear to be different from cardiac M2 and brain M2 receptors.

Effect of galanin on the opossum lower esophageal sphincter

The objective of this investigation was to examine the effect of galanin on the resting tone and neurally mediated relaxation of the lower esophageal sphincter (LES) in anesthetized opossums. Galanin caused a dose-dependent rise in the sphincter pressure when given either intra-arterially or intravenously. The D50 of intra-arterial galanin was 1.OX10(-11) mols/kg. The rise in the sphincter pressure caused by galanin was not modified by atropine, phentolamine, methysergide, pyrilamine or indomethacin. Furthermore, the contractile response of galanin on the LES was also not affected by tetrodotoxin. The fall in the sphincter pressure in response to vagal efferent stimulation, intramural stimulation or esophageal distension was antagonized by galanin. The results of these studies suggest that, 1) galanin causes sphincter contraction by its direct action on the smooth muscle, and 2) galanin suppresses LES relaxation. These studies suggest that galanin may be an important neuropeptide for the modulation of resting tone and LES relaxation.

Atypical localization of myenteric neurons in the opossum lower esophageal sphincter

This study investigated sphincter-body differences in neuronal density and morphometry between the esophageal sphincter and body with a view to determining whether previously reported differences are authentic. The anatomical limits of the opossum lower esophageal sphincter were correlated with its physiological behavior by manometric demarcation. Following this, peeled whole mounts and paraffin and cryosections were used to study the morphology and morphometry of the esophageal myenteric plexus. Thirty animals were used and seven quantitated. The plexus of the esophageal body was located as usual in a plane between the longitudinal and circular muscle, which coincided with the plane of cleavage when these muscle layers were peeled apart for studying the plexus in whole mounts. In contrast, the plexus was located in several planes in the lower esophageal sphincter, which had no cleavage plane. Therefore, peeling the sphincter removes neurons and yields falsely low counts, making peel preparations of this region unsuitable for neuronal quantitation. In paraffin sections, the neuron density in the esophageal body 7 cm above the sphincter was 6,353 +/- 850/cm2, but decreased significantly to 2,254 +/- 353/cm2 at the 1-cm segment. In the lower esophageal sphincter, the neuronal count increased again to 8,530 +/- 1,606/cm2. Flash-frozen cryosections, which produced neuronal morphology similar to the in vivo condition, showed that there was no difference in neuronal size between esophageal body and sphincter. These studies show that atypical myenteric plexus localization causes spuriously low neuronal counts reported in the lower esophageal sphincter and that reported neuronal size differences are technique-dependent.

Effects of ranitidine on the enzyme cholinesterase and the rat anococcygeus muscle

Ranitidine in lower doses, (100 ng and 1 microgram) accelerated the rate of reaction of the enzyme acetylcholinesterase with the substrate acetylthiocholine. However, in higher doses (10 micrograms and 100 micrograms) it inhibited the enzyme activity. In rat anococcygeus muscle preparation, the responses to acetylcholine were significantly inhibited in lower doses whereas in higher doses there was a dose-dependent potentiation of the responses to acetylcholine by ranitidine. The responses to carbachol were however, not affected by ranitidine in the same preparation. Our data suggest cholinomimetic as well as cholinolytic activity of ranitidine.

Intracellular studies of electrical membrane properties of opossum esophageal circular smooth muscle

It has been suggested that regional differences in membrane properties of circular esophageal smooth muscle play an important role in the mechanism of esophageal peristalsis. The purpose of this study was to examine both the passive and active membrane properties of circular smooth muscle at proximal and distal esophageal sites so as to delineate the role of myogenic properties in the intramural mechanism of peristalsis. Intracellular recordings were made in circular muscle strips taken from proximal (8 cm above the gastroesophageal junction) and distal (2 cm above the gastroesophageal junction) sites in 10 opossums using the partition method of Abe and Tomita. At both esophageal sites, determinations were made of resting membrane potentials, time constants, space constants, thresholds for action potentials, action potential amplitudes, rates of rise of action potentials, and action potential durations at half-amplitude. The values for these parameters at the proximal and distal sites, respectively, were as follows: mean resting membrane potential, 49.7 +/- 0.24 and 49.5 +/- 0.3 mV; length constant, 4.0 +/- 0.4 and 3.8 +/- 0.4 mm; time constant, 513 +/- 49 and 456 +/- 53 ms; threshold for action potentials, 9.3 +/- 0.4 and 8.8 +/- 0.3 mV; amplitude of action potentials, 36.0 +/- 5.2 and 35.3 +/- 1.7 mV; rate of rise of action potentials, 2.3 +/- 0.3 and 2.6 +/- 0.4 mV/ms; duration of action potentials at half-amplitude, 5.0 +/- 1.2 and 4.1 +/- 0.4 ms; and the conduction velocity for evoked potentials, 3.9 +/- 0.3 and 3.8 +/- 0.4 cm/s. Our studies show that there are no differences between proximal and distal esophageal sites in any of these determinations. These studies also show that regional differences in the electrical membrane properties of circular smooth muscle do not account for esophageal peristalsis.

Effect of tri-iodothyronine on cardiac responses to adrenergic-agonists in STZ-induced diabetic rats

Diabetes can produce a state of hypothyroidism which is known to alter adrenoceptor activity in rat hearts. We studied the effect of six-week STZ-induced diabetes on responsiveness to adrenergic agonists and also determined if tri-iodothyronine (T3) treatment for 6 weeks could modify these responses. T3 treatment produced a marked tachycardia and a slight but significant decrease in serum glucose and serum lipids in diabetic rat. Methoxamine produced positive inotropic and positive chronotropic effects in untreated control left and right atria, respectively. These effects were significantly increased in untreated diabetic preparations. T3 treatment for 6 weeks in diabetic rats prevented this effect. Isoproterenol also produced a dose-dependent positive inotropic and positive chronotropic effect in untreated control left and right atria, respectively. These responses were attenuated in untreated diabetic preparations. T3 treatment by itself decreased the responsiveness to isoproterenol in control left atria and further decreased the responses to isoproterenol in diabetic left atria. Similarly, in diabetic right atria T3 treatment did not produce any alteration in the responses to isoproterenol. The results indicate that only some of the diabetes-induced alterations in adrenoceptor activity can be associated with hypothyroidism.

An epidemiological study of psychiatric disorders in rural faridkot (punjab)

Epidemiological study of priority psychiatric disorders in a rural area of Faridkot it described. Prevalence is found to be 22.12 per thousand and this is comparable to figures reported by other studies. The prevalence is highest in age group of 35-44, males are more affected than females, and prevalence it more in widows and divorced. Psychiatric morbidity is found to be more in nuclear families as compared to joint families. Among various diagnostic categories prevalence of Manic depressive psychoses (13.08 per thousand) is found to be most common. The implications of the above observations are discussed and compared with the previous reported studies.

A rapid silver-free method for staining the myenteric plexus

A method is presented for the relatively rapid demonstration of the myenteric plexus. Saturated Sudan black B in 70% ethanol followed by 0.01% aqueous buffered thionein were used on intestinal peels (whole-mounts) to stain myelinated and unmyelinated fibers and neuron cell bodies, respectively. In contrast to accepted silver methods, these two kinds of fibers were distinguished clearly; Schwann cell nuclei and nodes of Ranvier were visible. Preparations had the following attributes: relatively low optical density coupled with high visual contrast, freedom from metallic "mirroring," low background staining of subjacent muscle fibers, and presentation of a polychromatic picture. The entire procedure was under the complete and repeatable control of the operator. Perikaryon and nuclear morphology were clearly demonstrated. The limitations of this method are that it does not provide good visualization of individual unmyelinated neuronal processes and does not permit preparation of permanent slides.

Experimental induction of isolated lower esophageal sphincter relaxation in anesthetized opossums

Isolated lower esophageal sphincter (LES) relaxation, defined as a transient sphincteric relaxation unaccompanied by esophageal peristalsis, has been shown to precede most episodes of gastroesophageal reflux in humans. We studied the genesis of isolated LES relaxation in anesthetized opossums by observing the response of four components of the deglutition reflex (mylohyoid electrical activity, pharyngeal contraction, esophageal peristalsis, and LES relaxation) to pharyngeal tactile stimulation, electrical stimulation of superior laryngeal nerve (SLN) afferents or cervical vagal efferents, and to balloon distention of the esophageal body. A single pharyngeal stroking evoked isolated LES relaxation in 56% of 160 instances. The proportion of isolated relaxations in response to SLN electrical stimulation varied inversely with the stimulus frequency, occurring in 64% of the responses at 5 Hz and 4% of the responses at 30 Hz. A full four-component deglutition sequence was most likely to occur at the higher frequencies of SLN electrical stimulation. Esophageal balloon distention elicited isolated LES relaxations or no response at low distending volumes, whereas at higher volumes LES relaxation and esophageal contraction predominated. Isolated LES relaxation had significantly less magnitude than relaxations accompanied by esophageal contractions. Bilateral cervical vagotomy abolished all LES and esophageal body responses induced by pharyngeal stroking and SLN stimulation, and rendered the esophageal body and LES less responsive to small volumes of distention. Vagal efferent stimulation produced isolated LES relaxation at lower frequency stimulation and LES relaxation with esophageal contractions at higher frequency stimulation. These studies show that isolated LES relaxation represents incomplete expression of either the deglutitive reflex or the peripheral reflex mediating secondary peristalsis.

Effects of hydralazine on streptozotocin-induced diabetic rats: prevention of hyperlipidemia and improvement in cardiac function

The effects of hydralazine on blood lipids, systolic pressure and cardiac performance were assessed in male Wistar rats, 6 weeks after they were made diabetic with streptozotocin (STZ). STZ-induced diabetes results in a loss of body weight, hyperglycemia and hypoinsulinemia. These effects are not altered after hydralazine treatment. STZ-diabetes also produced a significant bradycardia, elevation of blood pressure, hyperlipidemia and decreases in the levels of triiodothyronine and thyroxine. Hydralazine treatment successfully prevented all these alterations. In addition, cardiac performance was depressed in the untreated diabetic animals, but the cardiac performance of the hydralazine-treated diabetic animals showed a definite improvement. Thus, hydralazine controlled the high serum lipids and blood pressure and improved cardiac performance in STZ diabetic rats.

Role of substance P nerves in longitudinal smooth muscle contractions of the esophagus

Longitudinal muscle strips from different sites along the opossum esophagus were stimulated transmurally so as to produce neurally mediated contractions. Low-frequency transmural stimulation produced contractions after termination of the stimulus ("off" contractions), whereas high-frequency stimuli produced contractions beginning during the stimulus and extending beyond termination of the stimulus (extended-duration contractions). The intrastimulus portion of the extended-duration contraction was partially antagonized by atropine or substance P desensitization, whereas the poststimulus portion of the contraction was selectively and fully antagonized by desensitization with substance P. A combination of atropine and substance P desensitization abolished the extended-duration contraction. The amplitude of contraction was greater in the proximal than in the distal strips, irrespective of the mode of stimulation. The poststimulus portion of the extended-duration contraction was significantly longer in muscle strips taken from more distal than proximal portions of the esophagus. This gradient in duration of contractions was abolished by substance P desensitization but was not affected by atropine. Exogenously applied substance P (10 microM) produced equally sustained long-duration contractions at all sites along the esophagus. These observations suggest that a) both acetylcholine- and substance P-containing nerves are responsible for the extended-duration contraction of longitudinal muscle, and b) transmural stimulation causes an aborally directed increase in the duration of contractions; this gradient of increasing duration of contraction appears to be due to a more prolonged neural release of substance P at more distal sites.

Effects of [Na+] and [Ca2+] on the responses to milrinone in rat cardiac preparations

In the present investigation we have studied the influence of changing the [Ca2+] and [Na+] on the cardiac responses to milrinone in various preparations of rat heart. Milrinone (5 X 10(-5) to 8 X 10(-4) M) produced a dose-dependent positive chronotropic effect on right atrium and a positive inotropic effect on left atrium and papillary muscle of the rat. A decrease in [Ca2+] (from 2.2 to 1.1 mM) or an increase in [Na+] (from 120 to 60 mM) increased the milrinone-induced inotropic effect in left atrium and papillary muscle. However, in right atrium the chronotropic effect of milrinone was significantly decreased under these conditions. Opposite changes to milrinone-induced responses were observed when [Ca2+] was increased (to 3.3 mM) or when the [Na+] was decreased to 60 mM. Nifedipine (3 X 10(-3) M), a selective Ca2+ channel blocker, significantly inhibited the chronotropic response to milrinone in right atrium. However, the inotropic response to milrinone was found to be significantly greater in the presence of nifedipine. A veratridine-induced positive inotropic effect in the left atrium was also significantly increased in the presence of nifedipine. Tetrodotoxin (TTX, 1 X 10(-6) M), a fast sodium channel blocker, significantly reduced the inotropic response to milrinone in left atrium and papillary muscle. A milrinone-induced dose-dependent increase in the baseline tension was observed in the right atrium which was abolished in low [Ca2+] and significantly increased in high [Ca2+]. Our data suggest the possibility that milrinone increases Ca2+ influx in the right atrium to cause the chronotropic effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Structure-activity relationship of subtypes of cholecystokinin receptors in the cat lower esophageal sphincter

Cholecystokinin (CCK) causes relaxation of the cat lower esophageal sphincter (LES) by stimulating CCK receptors on the noncholinergic, nonadrenergic inhibitory neurons and causes contraction by stimulating CCK receptors on the sphincter muscle. Studies were performed in anesthetized cats to identify differences between the two CCK receptors by investigating the structure-activity relationships of various fragments of CCK or gastrin molecule. Lower esophageal sphincter pressures were monitored continuously, using continuously perfused catheters, and agents were administered intravenously or close intraarterially. Based on their doses and the presence or absence of tetrodotoxin pretreatment, CCK analogues produced either relaxation or contraction of the sphincter. The relative potencies of CCK analogues on the inhibitory (neural) response were CCK-8 greater than G-17-I greater than or equal to dCCK greater than CCK-4(1:1/14,000: 1/15,000: 1/335,000). Sulfated gastrin was nearly as potent as CCK-8. The relative potency of these agents on the contractile (muscle) response was CCK-8 = G-17-I greater than or equal to dCCK-8 greater than CCK-4 (1:1:1/4.5: 1/2000). Deamidated CCK-8 was inactive. Proglumide shifted the dose-response curves of the inhibitory as well as excitatory effects of CCK analogues to the right. These studies show that there are two distinct species of CCK receptors: (a) The CCK alpha receptors, present on the inhibitory neurons, are very discriminative and are critically dependent on SO4; and (b) the CCK beta receptors, present on the sphincter muscle, are not discriminative and are not critically dependent on SO4. Nonsulfated gastrin may share the CCK beta receptors with CCK.

Effects of chronic streptozotocin-induced diabetes on the cardiac responses to milrinone

We have studied the effects of milrinone on various cardiac preparations obtained from 6-week streptozotocin diabetic rats. The basal rate of spontaneously beating right atrium from diabetics was significantly lower as compared with controls. Milrinone (5 X 10(-5) to 8 X 10(-4) M) produced a dose-dependent positive inotropic and positive chronotropic effect in left atrium and right atrium, respectively. The positive chronotropic response to milrinone was slightly increased in right atria from diabetic animals. In papillary muscle neither the maximum response nor the pD2 value of milrinone was altered significantly in diabetic animals. The pD2 values of milrinone in right atrium and left atrium were found to be significantly higher in diabetic preparations compared with controls. The data indicate that the responses to milrinone are either unchanged or enhanced in hearts from diabetic animals.

Regional gradient of initial inhibition and refractoriness in esophageal smooth muscle

The influence of two successive vagal stimuli on esophageal contractions was studied by recording intraluminal pressures in the smooth muscle portion of the opossum esophagus. The esophageal contraction in response to the first or second stimulus in a pair of vagal stimuli was inhibited depending on the interstimulus interval, the frequency of the stimulus, and the esophageal site. The esophageal contraction in response to the first vagal stimulus was inhibited by a second vagal stimulus if the latter stimulus was applied before the peak of the first contraction. This phenomenon is termed initial inhibition. Initial inhibition is a graded phenomenon. It was greater at higher frequencies than at lower frequencies (p less than 0.001), and was significantly greater in the distal esophagus than in the proximal esophagus (p less than 0.01). The term "refractoriness" has been used to denote inhibition of the second esophageal contraction by the first. Refractoriness was observed during and beyond the duration of the first esophageal response. Refractoriness was also observed at all esophageal levels; however, the interstimulus intervals that demonstrated refractoriness were significantly greater in the distal than in the proximal esophagus (p less than 0.01). Refractoriness was complete (effective refractory period) during the ascending phase of the first contraction. Refractoriness was incomplete after the peak of the contraction (relative refractory period). These studies show gradients of durations and degrees of initial inhibition and refractoriness along the esophagus. The gradient is responsible for the peristaltic nature of esophageal contraction. The gradients of initial inhibition and refractoriness determine esophageal response to multiple successive swallows.

Swallow-evoked action potentials in vagal preganglionic efferents

Swallow-evoked potentials in the preganglionic vagal fibers were studied using the single-fiber recording technique in anesthetized opossums. Swallows were evoked by tactile pharyngeal stimulation or electrical stimulation of the cut central end of the superior laryngeal nerve (SLN). Swallowing activity was recorded by the mylohyoid electromyogram and esophageal motility. Sixty-six fibers were studied in which swallowing evoked action potentials. The latencies (from the onset of mylohyoid activity) of evoked responses in different fibers varied from 100 ms to 5 s. The discharge rate of the evoked response was 3-8 action potentials per burst. Each burst lasted 1.1 +/- 0.02 (SE)s. The latencies of evoked spike bursts showed a bimodal distribution. In 34 fibers the latencies were less than 1 s, and in 32 fibers the latencies ranged between 1 and 5 s; these are the short- and long-latency fibers, respectively. Short-latency fibers could easily be distinguished from long-latency fibers based on the influence of SLN-stimulus frequency. Short-latency discharges had low thresholds of activation and were sensitive to changes in the frequency of SLN stimulation, since their latencies decreased and their discharge rate increased with increasing SLN-stimulus frequency. On the other hand, the latencies and discharge rates of long-latency discharges were not modified with changing SLN stimulus frequencies. The conduction velocities of 6 short- and 9 long-latency fibers were 5.64 +/- 0.12 and 5.78 +/- 0.12 (SE) m/s, respectively (P greater than 0.05). The relationship between the latencies of swallow-evoked discharges in the short- and long-latency fibers and the esophageal smooth muscle responses suggested that the short-latency discharges may correlate with the latency of initial inhibition, and the long-latency fibers may correlate with latencies of peristaltic contractions. Based on these temporal relationships, we speculate that vagal efferent fibers showing swallow-evoked, short-latency discharges make contact with intramural inhibitory neurons. They may mediate deglutitive inhibition in the body of the esophagus, relaxation of the lower esophageal sphincter, and receptive relaxation of the fundus of the stomach. The fibers showing late discharges make contact with intramural excitatory neurons and participate in their sequential activation. This dual pathway of activation may be responsible for physiological esophageal peristalsis.

Swallowing induces sequential activation of esophageal longitudinal smooth muscle

We examined the mechanical activity of the longitudinal and circular muscles of the esophagus at three different levels (9, 5, and 1 cm above the lower esophageal sphincter) during peristalsis induced by swallows or vagal stimulation in anesthetized opossums with miniature strain gauges applied in the axis of muscle fibers. The onset of longitudinal muscle contraction occurred in an aboral sequence with swallows but simultaneously with vagal stimulation. The speed of longitudinal muscle activation with swallows was 7.6 +/- 1.7 cm/s. Circular muscle contraction occurred in an aboral sequence with vagal stimulation and swallowing with speeds of 4.1 +/- 0.8 and 2.3 +/- 0.1 cm/s, respectively. Longitudinal muscle contracted before the circular muscle at all sites. The duration of longitudinal muscle contraction increased aborally (P less than 0.05) with swallowing or vagal stimulation. These studies show that 1) during swallowing, esophageal longitudinal and circular smooth muscle contract in a sequential fashion, 2) the longitudinal muscle sequential contraction is due to central mechanisms, whereas circular muscle sequential contraction may be due to both central and peripheral mechanisms, and 3) peripheral neuromuscular mechanisms produce regional differences in the duration of longitudinal muscle contraction.

Pharmacologic identification, activation and antagonism of two muscarine receptor subtypes in the lower esophageal sphincter

Lower esophageal sphincter pressures were monitored with water-filled catheters in anesthetized opossums. Muscarinic agonists McN-A-343 and bethanechol were administered in the arterial supply of the sphincter. McN-A-343 caused relaxation after a brief contraction of the sphincter. Bethanechol caused a dose-dependent contraction. Tetrodotoxin antagonized the inhibitory effect of McN-A-343 but did not antagonized sphincter contraction caused by McN-A-343 or bethanechol. The mean ED50 values were 6.9 nmol/kg i.a. for McN-A-343-induced relaxation, 10.5 nmol/kg i.a. for McN-A-343-induced contraction and 0.4 nmol/kg i.a. for bethanechol-induced contraction. Atropine caused a dose-dependent rightward shift in the dose-response curves of inhibitory and excitatory effects of the two muscarinic agonists. Pirenzepine caused a dose-dependent rightward shift in the dose-response curves of McN-A-343-induced relaxation. Pirenzepine did not modify sphincter contraction caused by the muscarinic agonists. 4-Diphenylacetoxy-N-methylpiperidine methiodide, on the other hand, did not modify McN-A-343-induced sphincter relaxation but caused dose-dependent rightward shifts in the dose-response curves of sphincter contraction caused by McN-A-343 or bethanechol. These studies suggest that there are two distinct types of muscarine receptors in the opossum lower esophageal sphincter. The M1 muscarine receptors are present on the inhibitory neurons and participate in the synaptic transmission between vagal preganglionic and intramural postganglionic inhibitory neurons. They are activated by McN-A-343 and antagonized by pirenzepine. The M2 muscarine receptors are located directly on the sphincter muscle. They are also activated by McN-A-343, but are selectively activated by bethanechol and are antagonized by 4-diphenylacetoxy-N-methylpiperidine methiodide.

Intramural mechanism of esophageal peristalsis: roles of cholinergic and noncholinergic nerves

We examined the role of peripheral cholinergic and noncholinergic mechanisms in esophageal peristalsis. Intramural nerve elements in rings of circular muscle from six different levels of the opossum esophagus were stimulated transmurally so as to cause neurally mediated muscle contractions. Stimulus frequency was varied from 2 to 40 Hz. An increase in stimulus frequency caused an increase in latencies of contractions in rings from distal esophageal sites and a decrease in latencies in rings from proximal sites. This resulted in a marked slowing of the calculated peristaltic speed. Increasing stimulus frequency also caused an increase in duration and amplitude of contractions. These effects were reversed by atropine (0.1 microM), suggesting that higher stimulus frequencies recruited more cholinergic nerves. In the presence of atropine, increasing the stimulus frequency caused an increase in latencies of contraction at all sites, suggesting that increasing stimulation frequency applied to noncholinergic nerves causes an increase in latencies of contraction at all sites. The results of this study indicate that both noncholinergic and cholinergic nerves play a role in the peripheral mechanism of esophageal peristalsis. Cholinergic nerve stimulation reduces the latency and enhances the amplitude and duration of contractions seen with noncholinergic nerve stimulation alone. The influence of cholinergic innervation is most prominent proximally and decreases distally along the smooth muscle portion of the esophagus. This peripherally located gradient of cholinergic innervation plays an important role in determining the speed and amplitude of esophageal peristalsis.

Acetylcholinesterase and choline acetyltransferase staining of neurons in the opossum esophagus

The purpose of the present investigation was to identify and compare cholinergic intramural neurons in the lower esophageal sphincter and esophageal body by histochemical staining for acetylcholinesterase and the enzyme that synthesizes acetylcholine, choline acetyltransferase. Opossums were anesthetized and their abdominal cavity was opened by a midline incision to expose the esophagogastric junction. The lower esophageal sphincter was identified manometerically and localized in situ with markers. Tissues were removed, rapidly frozen in freon cooled with liquid nitrogen and serial cryostat sections were obtained from the lower esophageal sphincter and esophageal body. Sections were stained with one of the above histochemical procedures and adjacent sections were stained with Solachrome cyanin , which differentially stains nerve elements from muscle fibers. The muscle of the lower esophageal sphincter and esophageal body was stained with nonspecific cholinesterase with some selectivity of intensity of reaction in the various smooth muscle layers. All identifiable plexus neurons in the esophagus stained for nonspecific cholinesterase and acetylcholinesterase. Nerve fiber tracts were also stained for acetylcholinesterase within the longitudinal and circular layers of the tunica muscularis. Reaction for choline acetyltransferase showed no staining in the muscle layers or nerve fiber tracts of either part of the esophagus studied; however, selected neurons within the myenteric plexus of both regions (approximately 38%) were reactive. There was no significant difference in the number of positive choline acetyltransferase neurons in the lower esophageal sphincter or esophageal body.

Characteristics of "on" and "off" contractions in esophageal circular muscle in vitro

The prevalence, amplitude, and latency periods of "on," "off," and "intermediate" contractions in response to transmural stimulation were recorded in transverse rings of circular muscle from different levels of the opossum esophagus. Ten-second train stimuli consistently produced off contractions. On contractions were not seen at lower stimulus frequencies (2 and 5 Hz); however, their incidence approached 90% at higher frequencies (40 Hz). Intermediate contractions occurred only at stimulus frequencies of 10 Hz or greater and were less frequent than on contractions. In general, the on and intermediate contractions had significantly lower amplitudes than the off contraction. The on contraction occurred with a latency period from initiation of the stimulus. This latency was greater in the more distal sites and decreased with increasing stimulus frequency. The off contractions occurred with a latency period from termination of the stimulus. This latency was not dependent on either stimulus frequency or site along the esophagus. Atropine antagonized the on and intermediate contractions but had no such effect on the off contraction. Tetrodotoxin abolished the on, off, and intermediate contractions. This study suggests that an intramural mechanism exists that upon stimulation produces atropine-sensitive on contractions. These contractions may play a role in esophageal peristalsis.

Mechanical and electrical activity of esophageal smooth muscle during peristalsis

Mechanical events and membrane potential changes in response to evoked swallows and cervical vagal stimulation (10 and 40 Hz) were recorded in anesthetized opossums. Miniature strain-gauge transducers monitored the mechanical activity of the two layers. A suction electrode recorded from the intact esophagus, from a proximally based pedicle flap of longitudinal muscle (LM), and from circular muscle (CM). The onset of swallowing was marked by the onset of mylohyoid activity. During swallows LM contraction preceded CM contraction and was of longer duration. The latencies of LM and CM contraction were 1,980 +/- 38 and 2,250 +/- 101 ms, respectively. The durations of contraction of LM and CM were 5,590 +/- 260 and 3,330 +/- 67 ms, respectively. LM showed no hyperpolarization but showed depolarization and spike burst. The CM showed prompt hyperpolarization followed by depolarization and spike burst. Responses to vagal stimulation were qualitatively similar to swallows. The different components of the responses were quantitatively modified by changes in stimulus frequency. These studies show that, during peristalsis in response to swallows and vagal stimulation, 1) LM contraction occurs before CM and is of longer duration, and 2) unlike CM, LM does not hyperpolarize prior to depolarization.