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Biomedical subjects

P Bass

Publications and source records attributed to P Bass.

At least 73 records · Page 4Linked to original sources
PubMed1987

Gastric emptying of nondigestible solids in the fasted dog.

Gastric emptying of nondigestible solid particles was studied in the fasted dog. Particles of varying sizes (0.5-6.4 mm), density (0.5-2.9 gm/cm3), and surface characteristics were coadministered orally with 50 mL of saline and collected from a permanent duodenal cannula implanted approximately 15 cm from the gastroduodenal junction. The phase of the motility pattern was ascertained by the appearance of bile, which occurs during phase II, as well as by mucus discharge, which stops at the onset of phase I. A lag phase, due to the 'quiet' phase I, was observed in the gastric emptying of coadministered saline. This is in contrast with gastric processing of large volumes (i.e., greater than 200 mL) which can usually be approximated by first-order discharge. Most coadministered saline was discharged before the solid particles. The pH of the duodenal effluent was elevated approximately 1 pH unit during mucus discharge and its pH can be as high as 8.3. In the fasted dog, gastric emptying of nondigestible particles closely followed the gastric motility patterns. The onset of discharge of the particles correlated with the late phase II and the phase III activity. Except for a few cases, which took two migrating motor complexes (MMC), greater than 90% of administered particles was discharged from the stomach after one MMC. The discharged particles were entrapped within mucous plugs. In the fasted state, gastric emptying of nondigestible particles appeared to be independent of size, density, and surface characteristics. Mucus seems to play a significant role in the distribution and discharge of the administered particles.

Animals↗
PubMed1987

Effect of chemical ablation of myenteric neurons on neurotransmitter levels in the rat jejunum.

We have quantified neurotransmitter changes in the rat jejunum in which the myenteric neurons were ablated by serosal application of benzalkonium chloride. Within 2 days after benzalkonium chloride treatment, there was a 40% reduction in the activity of choline acetyltransferase, a specific marker for cholinergic neurons, and a 25% reduction in the amount of vasoactive intestinal peptide per centimeter length of jejunum. By 15 days, levels were comparable to those in control segments, and by 45 days after myenteric neuronal ablation, levels in treated tissues were twice those in controls. In contrast, we observed no reduction in the amount of leucine-enkephalin per centimeter length of jejunum at early times after benzalkonium chloride treatment, although by 45 days, levels of this neurotransmitter in treated segments of jejunum were more than twice those in controls. Significant increases in muscle thickness and tissue weight were also observed at 15, 30, and 45 days after myenteric neuronal ablation. Thus we have observed that in response to chemical ablation of myenteric neurons in the rat jejunum, there is a thickening of the smooth muscle layers and a compensatory increase in the production of certain neurotransmitters by the surviving neuronal elements in the gut.

Animals↗
PubMed1987

Adsorption of inorganic and organic ions to polycarbophil as a means of sustained-release dosage formulation.

The adsorption and desorption of drugs and inorganic ions to and from polycarbophil (PC), a polymer, were investigated to determine if PC would be a suitable carrier for sustained-release dosage formulations. Both in vitro and in vivo experiments with a polycarbophil-atropine sulfate complex demonstrated the gradual-release properties of this system. Adsorbed Cr3+ ions, like atropine, are released slowly. In contrast, 51CrO4(2-) ions are predominantly bound in an irreversible manner. A third group of drugs minimally adsorbed to PC under the conditions studied. We conclude that PC under both in vitro and in vivo conditions is able to bind certain ions and drugs and then release them over a period of time in a predictable and repeatable manner.

Acrylic Resins↗
PubMed1987

Cyanotic tetralogy of Fallot in a 77 year old man.

We report the clinical details of a 77 year old man with classical tetralogy of Fallot. The patient had clubbing and cyanosis at birth, and exertional squatting in childhood. He was asymptomatic as an adult until the seventh decade, when he developed biventricular failure and had an episode of bacterial endocarditis. He finally died of cerebral infarction and bronchopneumonia following abdominal surgery. In spite of investigations, the diagnosis was not made in life, but only discovered at post-mortem. A persistent ductus arteriosus was also found. Increased pulmonary blood flow via the ductus is believed to have facilitated this patient's unusual longevity.

Aged↗
PubMed1987

Temporal changes in mechanical properties of rat jejunal smooth muscle after myenteric plexus ablation.

We determined length-stress properties and active tension development of rat jejunal longitudinal and circular muscle at various times after myenteric neuron ablation. Myenteric neurons were destroyed by serosal application of benzalkonium chloride. Active tension generation in response to both carbachol and barium was depressed in both muscle layers up to 7 days after treatment, at which times the responses were normal. At 15 days, circular muscle responses were still comparable to control, but longitudinal muscle responses were significantly increased. Length-stress parameters of circular muscle were minimally affected, while those of longitudinal muscle were significantly altered 15 and 30 days after treatment. These alterations include changes in resting stress and increased active stress generation at both times. Our results suggest that 1) normal myenteric innervation is necessary for normal contractile activity in rat jejunal smooth muscle and 2) changes in cellular or tissue morphology or alterations in intracellular calcium homeostasis, as seen in other tissue, may occur after myenteric plexus ablation.

Animals↗
PubMed1987

Comparative laxation of psyllium with and without senna in an ambulatory constipated population.

Our short-term study used objective and subjective criteria to evaluate the ability of two laxative preparations to relieve constipation. Forty-two adults who were constipated, i.e., had less than or equal to 3 bowel movements during 1 wk of a single-blind placebo treatment, were randomized to receive psyllium (7.2 g/day) or psyllium plus senna (6.5 + 1.5 g/day). Both laxatives increased defecation frequency and wet and dry stool weights although the added effect of the senna was clearly evident. Only the psyllium with senna increased stool moisture. Two distinct responses to the psyllium plus senna were evident; the subpopulation of high responders (n = 7) was responsible for most of the increase in stool frequency and dry weight in this group, and laxation in the subpopulation of normal responders (n = 12) was similar to that observed in those receiving psyllium alone. Both laxatives provided a similarly high degree of subjective relief and improvement in stool consistency. When constipation was assessed objectively by stool frequency and weight, laxation was attained by 63% of the psyllium plus senna group and 48% of the psyllium group.

Adult↗
PubMed1986

Differentiation between myenteric plexus and longitudinal muscle of the rat jejunum as the site of action of putative enteric neurotransmitters.

The contribution of the myenteric plexus in the mechanical responses of rat jejunal longitudinal muscle produced by several enteric nerve substances was evaluated. The myenteric plexus of a segment of rat jejunum was destroyed by serosal application of benzalkonium chloride (BAC). Fifteen days after BAC treatment, both the BAC-treated and an orad control jejunal segment were removed and the mechanical responses of the longitudinal muscle produced by the following substances were examined: substance P, acetylcholine (ACh), 5-hydroxytryptamine (5-HT), cholecystokinin octapeptide (CCK-8), norepinephrine, vasoactive intestinal peptide (VIP), bombesin, [Leu5]enkephalin and somatostatin. Our results indicate that: substance P and norepinephrine produce their mechanical responses by acting predominantly on the longitudinal smooth muscle; 5-HT, CCK-8, ATP, VIP and neurotensin act predominantly through the myenteric plexus; ACh possesses both direct and indirect actions; and because the responses to [Leu5]enkephalin, bombesin and somatostatin were equivocal, a conclusion as to their site of action could not be made with this preparation.

Acetylcholine↗
PubMed1986

Effects of laxative and nonlaxative hydrophilic polymers on canine small intestinal motor activity.

Bulk-forming laxatives increase fecal volume and elicit aborally directed colonic motility patterns. Recently, it was demonstrated that test meals of the bulk-laxative fibers (cellulose and bran) elicited organized jejunal motor activity while nonlaxative fiber meals (guar) elicited unorganized jejunal motor activity. However, whether bulk-forming laxatives, as a class of compounds, differentially affect small intestinal motility has not been studied. Therefore, a study was made of the effects of the bulk laxatives psyllium and polycarbophil and the nonlaxative pectin on canine jejunal motor activity. Psyllium and pectin are examples of dietary fiber, while polycarbophil is a synthetic polymer. Pectin and psyllium test meals presented as viscous gels. In contrast, polycarbophil meals presented as a combination of discrete particles plus meal water. After each meal, measurements were made of the jejunal motility index, the time of reappearance of interdigestive burst activity, and overall motility patterns. Pectin and psyllium meals increased in viscosity as meal fiber content increased. As meal content and hence viscosity increased, both the laxative (psyllium) and nonlaxative (pectin) fiber meals elicited increasing jejunal motor activity and delays in the reappearance of the burst interval. For both fiber types, motor activity presented as randomly appearing contractions. In contrast, meals of the laxative polycarbophil elicited no more motor activity than the saline control meal. However, this control-level amount of activity presented as propagated clusters of contractions, ie, the "laxative-induced pattern." Polycarbophil did not delay the reappearance of burst activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylic Resins↗
PubMed1986

Human electrogastrograms. Comparison of surface and mucosal recordings.

A method to record the gastric basic electrical rhythm (BER) using skin electrodes is described. Correlation is made with mucosal suction electrodes in 20 volunteers. Successful simultaneous recording from surface electrodes and mucosal electrodes is made in 16/20 subjects (80%). An increase in amplitude of the recorded gastric BER with gastric contractions is demonstrated and discussed. Five patients with gastric motility disturbances and chronic nausea are also investigated. Four of these patients had diabetic gastroparesis. Each had preservation of the gastric BER. The rate was usually normal at three per minute, but during acute nausea episodes which occurred in three of the four, an abnormally increased rate of the BER (tachygastria) was seen. This finding was also seen in a subject with atrophic gastritis and delay of gastric emptying. The surface electrogastrogram may prove to be a useful tool for the investigation of patients with suspected gastric arrhythmias.

Abdominal Muscles↗
PubMed1986

Gastric motility is a major factor in cold restraint-induced lesion formation in rats.

These studies were performed to characterize the pattern of gastric contractility associated with cold restraint-induced lesion formation. Gastric motility in the rat was examined with extraluminal transducers at three sites of the stomach. The motility was monitored in the 24-h-fasted state, the postprandial state, and during cold-water immersion restraint. Gastric acid secretion was also monitored in a separate group of animals placed in cold restraint. Both feeding and cold restraint resulted in an equivalent increase in the amplitude of gastric contractions. Prolonged cold restraint, however, resulted in a distinct contractile pattern in which contractions were 56% less frequent and 300-400% longer in duration than those stimulated by feeding. All cold-restrained animals developed multiple gastric erosions. Cold restraint was not associated with increased acid secretion. A single subcutaneous injection of papaverine HCl (50 or 100 mg/kg) suppressed cold restraint-induced high-amplitude contractions and the cold restraint-induced lesion formation without altering acid secretion. These studies suggest that the stimulation of high-amplitude, prolonged duration contractions are more important than changes in gastric acid secretion in the formation of cold restraint-induced gastric lesions.

Animals↗
PubMed1986

Pharmacological characterization of rat jejunal contractility after chronic ablation of the myenteric plexus.

The authors have pharmacologically characterized longitudinal muscle contractility of the isolated rat jejunum chronically devoid of myenteric neurons. The myenteric plexus of a 3- to 4-cm segment of rat jejunum was ablated by serosal application of the cationic surfactant benzalkonium chloride (BAC). Fifteen days after treatment, both BAC-treated and untreated control jejunal segments were removed from each animal for pharmacological studies. BAC-treated tissues did not respond to the ganglionic stimulants nicotine, 1,1-dimethyl-4-phenylpiperazinium iodide and McN-A-343 or to the acetylcholinesterase inhibitor physostigmine. Short-pulse duration transmural electrical stimulation (0.1 msec) caused a frequency-dependent, tetrodotoxin-sensitive contraction in control but not BAC-treated tissues. Long-pulse duration transmural electrical stimulation (5.0 msec) contracted both control and BAC-treated jejunum. These contractions were partially reduced but not completely blocked by tetrodotoxin. To assess smooth muscle function, the mechanical responses to the muscarinic receptor agonist carbachol were examined. Carbachol contracted both control and BAC-treated tissues with maximal responses and ED50 values that were not significantly different. In addition, the maximal tension development produced by 10(-2) M barium chloride in similar lengths of control and BAC-treated jejunal segments was not significantly different. These studies demonstrate that chronic ablation of the myenteric plexus by serosal application of BAC essentially eliminates neuronally mediated responses without a concomitant alteration in longitudinal muscle contractility. Because nerve-mediated longitudinal muscle responses are lost despite the presence of an intact submucosal plexus in the BAC-treated jejunum, our data suggest that the motor neurons innervating the rat jejunal longitudinal muscle are located in the myenteric plexus.

(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
PubMed1986

Ablation of the myenteric plexus impairs alpha but not beta adrenergic receptor-mediated mechanical responses of rat jejunal longitudinal muscle.

The mechanical responses produced by alpha and beta adrenergic receptor agonists were evaluated in control and myenteric neuron-ablated rat jejunal longitudinal muscle. The myenteric plexus of the jejunum was destroyed by serosal application of benzalkonium chloride (BAC). The beta adrenergic receptor agonists isoproterenol and sulfonterol produced a concentration-dependent relaxation of both control and BAC-treated jejunum. Dose-response curves obtained in control and BAC-treated jejunum were nearly superimposable regardless of the beta agonist used. Isoproterenol-induced relaxation was antagonized by the beta receptor antagonists propranolol and practolol but not by butoxamine. The alpha-1 selective agonists phenylephrine and methoxamine were more potent and efficacious in producing relaxation of control than BAC-treated jejunum. The relaxant responses of methoxamine and phenylephrine in control jejunum were blocked by prazosin but not by yohimbine. The supposed alpha-2 selective agonist clonidine also produced a concentration-dependent, prazosin-sensitive, yohimbine-resistant relaxation which was markedly greater in control than BAC-treated jejunum, consistent with alpha-1 receptor stimulation. Clonidine tested in the presence of prazosin and the alpha-2 selective receptor agonists UK-14,304, M-7 and B-HT 920 all produced a concentration-dependent contraction of control but not BAC-treated jejunum. The contractile response produced by UK-14,304 was antagonized by yohimbine but not by atropine. Our results suggest that in rat jejunal longitudinal muscle: beta adrenergic receptors mediate relaxation and are located on the smooth muscle; alpha-1 adrenergic receptors mediate relaxation and are located on both the smooth muscle and myenteric plexus.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗
PubMed1985

Canine gastric emptying of polycarbophil: an indigestible, particulate substance.

We tested whether indigestible solids could empty from the canine stomach independently of gastric burst motor activity. Test meals contained polycarbophil, an indigestible particulate (1-3 mm diameter) substance. Test meals were slurries of 30 or 90 g of radiolabeled polycarbophil particles in saline. Meals were administered via an oral gastric tube. After 4 h, the stomach was drained via a gastric cannula, and the percentage of meal that had emptied into the duodenum was calculated. Antroduodenal motor responses to the meals were monitored with strain-gage force transducers. The motor responses to polycarbophil meals were compared with those after canned food and saline meals. Fifty percent of the 90-g polycarbophil meal emptied by 4 h; this occurred independently of gastric burst motor activity. Both polycarbophil and canned food elicited similar indexed motor responses and both delayed the postprandial reappearance of gastric burst motor activity. We conclude that small indigestible particles can stimulate fed state-like motility and empty from the stomach independently of gastric burst activity.

Acrylic Resins↗
PubMed1985

Use of gut cyclic motor activity to evaluate a stimulant (narcotic) and inhibitor (anticholinergic) of gastrointestinal-tract activity in the unanesthetized dog.

The use of gut cyclic motor activity to evaluate both a stimulant and inhibitor of gastrointestinal contractile activity in the unanesthetized dog is described. In the interdigestive (fasted) state, there is a cyclic alternation of intense periods of contractions (burst) with quiescent periods (basal). Codeine phosphate, a narcotic agent, caused a dose-dependent increase in the number and duration of circular muscle contractions when administered in the basal phase. Hyoscine N-butyl-bromide, an anticholinergic drug, caused a dose-dependent reduction in both amplitude and frequency of burst-phase contractions. When a combination of codeine phosphate and hyoscine N-butylbromide was administered simultaneously in the basal or burst phase, the hyoscine N-butylbromide prevailed and had the dominant effect. This is a useful in vivo model to evaluate the effects of drugs on the gastrointestinal tract.

Animals↗
PubMed1985

Canine gastric emptying of fiber meals: influence of meal viscosity and antroduodenal motility.

Dietary fibers such as psyllium and guar gum have been shown to delay the gastric emptying of liquids and solids, presumably due to an increase in meal viscosity. For liquid test meals containing fats, delayed gastric emptying is associated with a reversal of the usual antral-to-duodenal contractile gradient. The present studies were performed to determine whether the gastric emptying of increasingly viscous psyllium and guar gum meals was associated with antroduodenal motility changes. Dogs were surgically fitted with mid-duodenal cannulas for the measurement of gastric emptying. Strain-gauge force transducers were used to monitor antral and duodenal contractile responses to the test meals. Low-viscosity fiber meals emptied from the stomach rapidly (E 1/2 approximately 10 min) compared with the high-viscosity meals (E 1/2 approximately 40 min). None of the test meals stimulated antral or duodenal motility despite differences in gastric emptying time. Other motor parameters such as the time of reappearance and the duration of the burst interval were also unchanged. We conclude a) as test meals' fiber content and viscosity increase, gastric emptying is slowed; and b) viscosity-related delays in gastric emptying are not due to an effect on postprandial antroduodenal motility.

Animals↗
PubMed1984

Human surface electrogastrograms: ac and dc measurements.

Both ac and dc abdominal electrical recordings were made on fasted and fed human subjects using a spatial array of 18 cutaneous, biopotential electrodes. Controlled skin puncture minimized cutaneous potentials. Pregelling electrodes minimized drift. The recording sessions were between two and three hours in length. We determined the optimal location for ac recording of a 3 cpm wave at a location on the midline approximately 5 cm below the xiphoid process. Seven cpm waves were also observed in one individual at the same location. The dc values were fed into a Hewlett Packard 1000 computer which interpolated the intermediate values and plotted two-dimensional contour plots which were examined visually. The right abdominal surface was typically 1.8 mV more negative than the left for prefeeding. The left abdominal surface was typically 4.6 mV more negative than the right for postfeeding. We propose an electrical model that explains these results during the fasted state.

Abdomen↗