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Biomedical subjects

J Christensen

Publications and source records attributed to J Christensen.

At least 271 records · Page 15Linked to original sources
PubMed1976

Intestinal propulsion in the dog. Its relation to food intake and the migratory myoelectric complex.

We studied electrical events and flow in the canine small intestine in vivo. The transit of a small radioactive bolus injected into the jejunum was monitored by counting from a Biebl loop. After feeding, the rate of propulsion of the bolus varied within a narrow range. When food and water were withheld for more than 12 hr, transit of the bolus hecame highly variable. The variability increased at about the same time as the onset of the migratory myoelectric complex associated with fasting. Electrical recordings from the intestinal muscle demonstrated that the bolus was propelled into the loop in advance of the band of intense spike potentials which travels along the small intestine in the fasted state. The bolus was cleared from the loop when the spike potentials reached this segment. Variability of transit after prolonged fasting can be explained by (1) variability in the rate of migration of the phase of intense spike potentials, and (2) the timing of the injection of the bolus in relation to the component phases of the electrical complex. Flow is highly dependent upon the electrical activity and the resulting contraction patterns of the small intestine, which are themselves dependent upon feeding.

Animals↗
PubMed1976

Histamine receptors in esophageal smooth muscle of the opossum.

Esophageal smooth muscle was examined for histamine receptors. The effects of histamine, the histamine analogs 4-methylhistamine (4-MH) and 2-(2-pyridyl) ethylamine (PEA), the histamine receptor antagonists mepyramine and metiamide, and the histamine-releasing substance compound 48/80, on lower esophageal sphincter (LES) and esophageal body (EB) smooth muscle of the opossum were studied in a superfused tissue bath. Histamine, PEA, an H1 receptor agonist, and compound 48/80 caused a dose-related increase in LES basal tension and in EB off response amplitude, the threshold for histamine being 6.7 X 10(-8) M and that for PEA being 6.7 X 10(-7) M. In the presence of mepyramine, and H1 receptor antagonist, the effects of histamine and compound 48/80 were reversed to inhibition of both LES basal tension and EB off response amplitude, while the effect of PEA was abolished. Metiamide, an H2 receptor antagonist, did not alter responses to histamine, PEA, or compound 48/80. The H2 receptor agonist 4-methylhistamine caused a reduction of LES tension and EB off response amplitude, but caused an increase in those parameters in the presence of metiamide. A combination of mepyramine and metiamide abolished responses to all agonist drugs. The results indicate that LES and EB smooth muscle contain both excitatory H1 and inhibitory H2 receptors for histamine. Endogenous histamine released from storage sites in LES and EB and exogenous histamine both preferentially activate H1 receptors.

Animals↗
PubMed1976

A dopamine receptor in esophageal smooth muscle of the opossum.

We examined the possibility that dopamine may play a role in nerve-mediated "off" responses of esophageal body (EB) and relaxations of lower esophageal spincter (LES) smooth muscle. The effects of dopamine, epinine, and dopamine antagonists on EB and LES smooth muscle were studied on these responses. Dopamine and epinine caused a dose-related fall in basal LES muscle tension and in amplitude of EB muscle "off" responses. Threshold dose for both was about 10(-7) M, and maximal dose was about 10(-4) M. At high concentrations, they also caused repetitive transient contractions of both LES and EB muscle after the period of inhibition. These effects were antagonized by haloperidol, 10(-5) M, and bulbocapnine, 10(-5) M, but were not influenced by propranolol, 10(-5) M, nor by phenoxybenzamine, 10(-5) M. Neither haloperidol nor bulbocapnine influenced responses to electrical field stimulation. Tetrodotoxin 10(-7) M abolished the responses to electrical field stimulation but did not antagonize the effects of dopamine and epinine. EB and LES smooth muscle contain a dopamine receptor. It is unlikely that dopamine is involved in responses to electrical field stimulation.

Animals↗
PubMed1975

An uncontrolled comparison of treatments for achalasia.

A series of 78 patients with achalasia, seen during a 10-year period, was like those reported by others with regard to age at onset, nature of symptoms, and duration of symptoms. Analysis of the results of 5 different treatment modalities administered allows an uncontrolled comparison heretofore not available from an institution at which no one treatment was favored over all others. Those who were not treated or who received only anticholinergic medication did not become asymptomatic. Those treated by single or repeated bougienage were not improved for more than a few weeks and suffered a 6% incidence of esophageal perforation. Forty-six per cent of those treated by a single pneumatic dilatation were asymptomatic for 1 year or more. Although esophagocardiomyotomy provided symptomatic relief for 1 year or more in 85%, there was a 25% incidence of gastroesophageal reflux.

Adolescent↗
PubMed1975

Pharmacology of the esophageal motor funciton.

In the striated muscle of the upper esophageal sphincter, tonic maintenance of closure is probably mediated via tonic central excitation of the extrinsic motor innervation; relaxation represents central inhibition of this mechanism. The motor nerves are probably cholinergic and act through nicotinic receptors like those of somatic striated muscle. In the striated muscle of the esophageal body, swallowing-induced contraction is also probably a cholinergic and nicotinic response. In the smooth muscle of the esophageal body, the control of contractions is cholinergic and muscarinic in part, but there is evidence for a nonadrenergic and noncholinergic component as well. The muscarinic component may arise from the cholinergic innervation of the longitudinal muscle layer. The other component may lie in the cryptic innervation of the circular muscular layer. In the smooth-muscled lower esophageal sphincter, resting closure tension appears to reflect a variety of possible control mechanisms. No single control system predominates. The evidence for muscarinic excitation is equivocal. An excitatory adrenergic alpha mechanism and inhibitory adrenergic beta receptors may contribute. A role for the polypeptide hormones from the gastrointestinal tract seems unlikely. Relaxation of the lower sphincter with swallowing seems not to involve any of these mechanisms, but is apparently accomplished by nonadrenergic noncholinergic inhibitory nerves like those present elsewhere in the gut (87). The possibility that the transmitter of these nerves is an adenine nucleotide has been raised from studies of other parts of the gut, but that hypothesis has not yet been examined critically in the lower esophageal sphincter.

Adrenergic alpha-Agonists↗
PubMed1975

Local specialization at ileocecal junction of the cat and opossum.

In 10 cats and 10 opossums, serial transverse strips of muscularis propria 2 mm wide, from about 1.5 cm above to about 1.5 cm below the ileocecal mucosal junction, were separately stretched to discover the relationship between length and tension and were separately subjected to electrical field stimulation. In both species, ileal strips showed stimulus relaxations, sometimes accompanied by contractions after the stimulus trains (off responses), whereas colonic strips generally did not. These responses were abolished by tetrodotoxin, 3 times 10-7 M in the opossum, 3 times 10-6 M in the cat. Length-tension slopes were greatest just above the ileocecal junction where stimulus relaxation occurred. Tetrodotoxin at 3 times 10-7 M raised basal tension in ileal strips in both species and in colonic strips only in the cat. Muscle of the ileocecal junction resembles that of the esophagogastric and gastroduodenal junctions in showing a relatively high degree of resistance to stretch and prominent neurogenic stimulus relaxation. However, the ileocecal junction, in contrast, also possesses a tonic inhibitory innervation.

Animals↗
PubMed1975

Longitudinal contractions in the duodenum: their fluid-mechanical function.

The hypothesis examined was that contractions of the longitudinal muscle layer occurin the duodenum which are independent of those of the circular muscle layer and that they induce flow of duodenal contents. A segment of opossum duodenum isolated in vitro was marked and photographed during periods of longitudinal muscle contraction, when the circular muscle layer appeared inactive. The prequency of longitudinal oscillation of the marked points was 20.5 cycles/min. The longitudinal displacement wave spread caudad with an average velocity of 3.27 cm/s. Frequency and velocity of electrical slow waves were determined in similiar duodenal segments. Slow-wave frquencywas 18.9 cycles/min. In a two-dimensional mechanical model, flow induced by simulatedlongitudinal muscle layer appear to be driven by the electrical slow waves of the duodenum. They are capable of inducing a pattern of flow in which ocntents flow betweenthe core and the periphery of the intestinal conduit.

Animals↗
PubMed1975

Phase lock of electrical slow waves and spike bursts in cat duodenum.

The phase relationship between slow waves and spike bursts was studied in vitro in the cat duodenum. Electrodes were arranged radially about the duodenum. Records were read for T1, the time between the slow-wave "valley" and the first spike, and T2, the time between successive valleys. The distributions of the ratio T1/T2 showed very small differences, not uniquely attributable to radial electrode position. The distribution of T1/T2 indicated that spike bursts began 58.8% of the way through a slow-wave cycle, measured from the valley. Also, electrodes were arranged longitudinally and records were read to determine deltaSW, the slow-wave delay time between adjacent electrode positions, and deltaS, the spike burst delay time between adjacent electrode positions. The correlation of deltaS and deltaSW suggested a linear relation, and a regression resulted in a good linear description. These results are consistent with an assumed phase lock of spike bursts to slow waves.

Animals↗
PubMed1975

Stochastic model of contractions at a point in the duodenum.

Contractions at one point in the human duodenum were studied as a time series. Manometric records were made over long time periods from the duodenum in fed human subjects. A 5-s grid was superimposed on the time axis of the records. Each 5-s interval was treated as a slow-wave cycle within which either a contraction or a no-contraction could occur. The resulting series of alternating runs of contractions and no-contractions was tested for the existence of trends. Trends were found indicating possible temporal dependence. A Markov-type model was used to try to generate data similar to the real data. Success was achieved by a model that assumed a probability of contraction dependent on the three previous slow-wave cycles. The frequency distributions obtained from the real and generated data were compared using Chi-square goodness-of-fit tests and found to be statistically similar. The correlations in time found for the contractions might be due to a time dependency in the controls for contraction over four successive slow-wave periods, 20 s in humans.

Animals↗
PubMed1975

Distributions of spike bursts in cat duodenum.

The histograms of spike bursts over short distances were examined in the isolated cat duodenum with multiple electrodes arranged circumferentially and longitudinally. At a single cross section of the duodenum, spike bursts occurred simultaneously in any single slow-wave cycle, but all eight monitored sites in the circumference participated simulatenously only in a bout 25% of the spike-burst cycles. There also were wide variations in the incidence of spike bursts at different locations in a planar cross section. In a longitudinal section, net level of activity over short distances varied widely. Also, spike bursts were out of phase in the longitudinal axis, appearing to spread caudad; 80% of spike burst groups involved less than an average of 5.5 consecutive electrode sites (spaced at 5-mm intervals). Since spike bursts seem to be correlated with ring contractions of the circular muscle, the fact that they appear sequentially in time along the duodenum indicates that such contractions must always be peristaltic. An estimated 80% of such contractions sweep less than about 3 cm. Records of spike bursts from a single electrode do not accurately reflect activity beyond that one point site.

Animals↗
PubMed1975

Three layers of the opossum stomach: responses to nerve stimulation.

The three muscle layers of the opossum stomach were compared in their responses to electrical field stimulation. Strips were cut from the muscular wall of the stomach with their longer axes in the direction of the longitudinal, circular, and oblique muscle layers and stimulated at 1-min intervals with 20-sec trains of 1-msec pulses at 10 Hz and supramaximal strength at 500 ma. Strips either contracted, relaxed, or did not respond during the stimulus trains. Responses were abolished by tetrodotoxin, 10(-6) M. Contractions, but not relaxations, were abolished by atropine, 10(-6) M. Relaxations were not antagonized by propranolol, tolazoline, or phenoxybenzamine. Thus, the responses represent excitation of both cholinergic excitatory and nonadrenergic inhibitory nerves. In strips cut longitudinally, cholinergic contractions occurred more frequently than in the other two kinds of strips. After atropine treatment, the incidence of relaxation was greater in strips cut in the direction of the oblique layer than in the other two groups. The results suggest that, of the two kinds of nerves, the cholinergic excitatory innervation is usually dominant in the longitudinal muscle layer, and that the nonadrenergic inhibitory innervation is more complete in the oblique muscle layer.

Animals↗