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Biomedical subjects

G W Scott

Publications and source records attributed to G W Scott.

At least 37 records · Page 2Linked to original sources
PubMed1984

The muscle layer of the canine gallbladder and cystic duct.

The muscle layer of the canine gallbladder wall and cystic duct was found to be a three-dimensional meshwork of smooth muscle bundles which appear loosely and irregularly arranged on the mucosal aspect and consolidate to form a homogeneous plate-like layer on the serosal aspect. The muscle bundles are tightly woven around interspersed pockets of loose connective tissue in the gallbladder wall and gradually become loosely arranged with more prominent amounts of intervening connective tissue in the cystic duct. The muscle layer is thickest in the gallbladder wall and becomes progressively thinner out into the cystic duct. No anatomic sphincter was observed. Ultrastructural organization revealed individual muscle fibers to be of irregular profile, often branching, widely spaced with intervening collagen fibers, and having few cell-to-cell contacts.

Animals↗
PubMed1984

Effects of histamine receptor stimulation on diseased gallbladder and cystic duct.

The effects of histamine receptor stimulation on the motility of diseased human gallbladder and cystic duct were studied on tissue strips in vitro. Histamine produced concentration-dependent contractions in normal tissues and in tissues from each disease group, but the sensitivity of the strips to histamine as measured by the median effective dose was dependent upon the grade of disease: normal, 90.0 microM; mild chronic cholecystitis, 32.4 microM; advanced chronic cholecystitis, 12.5 microM; and acute cholecystitis, 3.0 microM. There were no differences in histamine sensitivity among different regions (body, neck, and cystic duct) of the biliary system. Studies with receptor-selective agonists and antagonists indicated that the contractile effects were mediated via histamine H1 receptors. Histamine H2 receptor agonists caused only small relaxant responses in about 30% of strips from gallbladder body, but were without effect in gallbladder neck and cystic duct. We conclude that the effects of histamine on the motility of diseased human gallbladder may depend upon the severity of the cholecystitis.

Bile Duct Diseases↗
PubMed1983

Morphology of canine gallbladder. Scanning electron microscope observations on the epithelium.

Examination of the surface topography of canine gallbladder epithelium using the scanning electron microscope reveals subtle changes in the morphology of the cellular components between the full and empty states. In the full state large bays exist between relatively low, ridge-like crests or folds of mucosa which gradually increase in height as the gallbladder empties causing a subsequent reduction in size and volume of the bays. The relaxed gallbladder exhibits an irregular arrangement of tall, closely apposed mucosal folds with intervening deep valleys. The degree of apical convexity of individual epithelial cells will increase as the mucosal folds begin to relax. Other mucosal features most easily observed in the full state were small pit-like intraepithelial glands. The apical surfaces of the epithelial cells exhibit a densely uniform microvillus border and occasional membrane-bounded cytoplasmic protrusions (apical bullae) extending out into the lumen of the organ. The lateral cell membranes and basal lamina were also examined. Correlative methacrylate and transmission electron microscopic findings are included. The functional aspects of these morphological alterations and apical protrusions are discussed.

Animals↗
PubMed1983

Adenosine and ATP effects on isolated guinea pig gallbladder.

Effects of adenosine, ATP and several derivatives of adenosine were measured in isolated strips of guinea pig gallbladder. Adenosine caused relaxations which were antagonized by theophylline and potentiated by an inhibitor of adenosine uptake, 6-(1-hydroxy-5-nitrobenzylthio)-guanosine (HNBTG). Among several adenosine derivatives, 2-chloroadenosine and 5'-N-ethylcarboxy-midoadenosine were similarly effective while 1-N6-phenylisopropyladenosine was only a weak relaxant. None of the derivatives caused maximal relaxations at 100 microM, and thus absolute potencies could not be determined. ATP caused predominantly contractile effects, with relaxations sometimes being evident at high concentrations. Indomethacin abolished contractile effects of ATP, suggesting prostaglandin involvement, and only relaxations were evident in its presence. Adenosine deaminase abolished the effects of adenosine and partly reduced the relaxant effects of ATP in the presence of indomethacin. In view of the low potency of adenosine and ATP, physiological roles for these compounds in gallbladder motility are not readily evident.

Adenosine↗
PubMed1983

Cholecystokinin constricts the canine cystic duct.

The effects of cholecystokinin and cholecystokinin-octapeptide on the canine cystic duct have been studied. The resistance to flow through the duct in vivo, assessed by measuring the flow rate of saline that was perfused through the duct at constant pressure, was increased by cholecystokinin in a dose-dependent manner. Cholecystokinin also produced the well-recognized, dose-dependent elevations of gallbladder intraluminal pressure. Comparison of dose-response curves prepared in each animal indicated that the sensitivity of the cystic duct was significantly lower than that of the gallbladder. Isolated strips of cystic duct and gallbladder in vitro were contracted by cholecystokinin or cholecystokinin-octapeptide; again, cystic duct muscle displayed a lower sensitivity than gallbladder to the contractile effects of these agents. It is not known whether cholecystokinin can affect cystic duct resistance under physiologic conditions.

Animals↗
PubMed1982

Stimulatory and inhibitory histamine receptors in canine cystic duct.

1 The effects of histamine receptor stimulation were assessed on the resistance of the canine cystic duct in vivo and on the contractility of circular muscle preparations of canine cystic duct in vitro. 2 In anaesthetized dogs, the H1-receptor agonist, 2-pyridylethylamine (0.05 to 15 mumol, i.a.), elicited dose-dependent increases in cystic duct resistance, whereas the H2-receptor agonist, 4-methylhistamine (0.05 to 15 mumol, i.a.) decreased cystic duct resistance. These responses were antagonized by the H1-receptor antagonist, diphenhydramine, and the H2-receptor antagonist, cimetidine, respectively. 3 Histamine (0.1 to 3000 nmol, i.a.) also increased cystic duct resistance in vivo. In the presence of diphenhydramine, the stimulatory effect of histamine was antagonized and slight decreases in cystic duct resistance became apparent. Cimetidine or prazosin also antagonized the stimulatory effects of histamine. 4 Histamine (1 to 100 microM) or 2-pyridylethylamine (1 to 100 microM) contracted, whereas 4-methylhistamine (1 to 100 microM) relaxed, circular muscle preparations of cystic duct. These excitatory and inhibitory responses were antagonized by diphenhydramine and cimetidine, respectively. 5 These results indicate that the canine cystic duct possesses excitatory H1- and inhibitory H2-receptors. The predominant effect of histamine is an H1-receptor-mediated increase in cystic duct resistance. Histamine, which may be released in association with cholecystitis, may exert significant effects on the regulation of bile flow in and out of the gallbladder and may contribute to gallbladder stasis during biliary disease.

Animals↗
PubMed1980

The occurrence of postsynaptic alpha- and beta-adrenoceptors in the guinea-pig gall bladder.

1 Guinea-pig gall bladder strips were contracted by (-)-noradrenaline, 10(-5) M, and by field stimulation at 5 Hz (in the absence or presence of 10(-6) M atropine) and relaxed to 10(-5) M (-)-isoprenaline. (-)-Adrenaline, 10(-5) M, predominantly contracted, but sometimes relaxed, this preparation. 2 In the presence of 10(-6) M phentolamine, contractions to (-)-noradrenaline and to (-)-adrenaline were reversed to relaxations. The relaxations produced by (-)-isoprenaline were unaltered. In the presence of 10(-6) M propranolol, contractions to (-)-noradrenaline increased in magnitude, relaxations to (-)-adrenaline were reversed to contractions, and relaxations to (-)-isoprenaline were abolished. These results demonstrate the presence of postsynaptic alpha-adrenoceptors which mediate contractions, and postsynaptic beta-adrenoceptors which initiate relaxations, in the guinea-pig gall bladder. 3 The contractile responses to continuous field stimulation for 5 min at 5 Hz in Krebs solution alone were reduced in magnitude by propranolol, 10(-6) M. In the presence of 10(-6) M atropine (added to eliminate the cholinergic component of the response), propranolol, 10(-6) M, had no effect on responses to stimulation at 5 Hz. Thus propranolol reduced the response to cholinergic stimulation in this tissue; the basis of this effect is unclear. In the absence or presence of atropine (10(-6) M), the responses to 5 Hz were smaller in magnitude in the presence than absence of phentolamine, 10(-6) M. This suggests that the responses to field stimulation of the guinea-pig gall bladder may, in part, be due to the release of endogenous noradrenaline which acts at postsynaptic alpha-adrenoceptors.

Animals↗
PubMed1980

The effects of time and indomethacin on contractile responses of the guinea-pig gall bladder in vitro.

1. The effects of time and of indomethacin on contractile responses of the guinea-pig gall bladder were studied in vitro. 2. The tissues contracted to field stimulation at 5 Hz (in the absence and presence of atropine 10(-6) M). (-)-noradrenaline (10(-5) M), acetylcholine (10(-5) M), and adenosine 5'-triphosphate (ATP, 10(-4) M); the magnitude of the contractile responses increased with time. 3. (-)-Isoprenaline 10(-5) M either relaxed (17 of 23 preparations tested) or had no effect on gall bladder strips. 4. The responses of strips of guinea-pig gall bladder to field stimulation at 5 Hz (in the absence or presence of atropine 10(-6) M), (-)-noradrenaline (10(-5) M), and acetylcholine (10(-5) M) obtained 4 h 45 min after setting up the tissue were reduced following incubation with indomethacin (7.9 x 10(-6) M for 1 h). The responses to (-)-isoprenaline (10(-5) M) and to ATP (10(-4) M) were abolished by incubation with indomethacin. 5. These results suggest that, in the guinea-pig gall bladder in vitro, the magnitude of the contractile responses to field stimulation at 5 Hz, (-)-noradrenaline (10(-5) M), and acetylcholine (10(-5) M) and the ability of the tissue to respond to (-)-isoprenaline (10(-5) M) and ATP (10(-4) M), may be dependent on the synthesis of a prostaglandin-like substance.

Acetylcholine↗
PubMed1979

Neuroblastoma in adults.

Two cases of neuroblastoma are described in patients who were both more than 25 years old when their symptoms first appeared. The behaviour of this tumour appears less aggressive in adults than in children, but the cases presented illustrate its resistance to chemotherapy and radiotherapy, and surgery is suggested as the first line of treatment in adults, even if the growth cannot be removed completely.

Adrenal Gland Neoplasms↗
PubMed1979

Resistance and sphincter-like properties of the cystic duct.

The canine cystic duct, like that in man, has an extremely thin layer of muscle deep to the mucosal layer, surrounded by a dense layer of collagen fibers. The resistance to flow through the duct was studied in 16 anesthetized dogs by perfusing the duct with saline solution at constant pressure and recording the flow rate of the solution. The flow rate varied with respiratory movements, but there were also nonrespiratory variations which might be due to spontaneous sphincter-like contractions. Significant reductions in flow through the duct followed systemic intravenous or local intra-arterial injections of morphine or pharmacologic concentrations of adrenaline or cholecystokinin. It was concluded that an extremely small amount of muscle in the wall of the duct was capable of sphincter-like activity. The resistances to flow were the same in either direction through the duct, an indication that the prominent mucosal folds, valves of Heister, did not function as unidirectional valves. In view of the high resistance to flow through the duct and the possibility that sphincter-like activity may also occur under physiologic conditions, the function of the duct requires more attention than it has received in the past.

Animals↗
PubMed1977

Corynebacterium bovis as a cause of human disease.

Corynebacterium bovis is a gram-positive rod which can cause bovine mastitis and rancidity in cream. On only one occasion has this organism been reported to cause human disease. Six further cases are described in which infections were caused by C. bovis. In two patients the nervous system was involved; two patients had bacterial endocarditis; one had chronic otitis media; and one had a persistent leg ulcer. Five patients recovered completely from the infection; the other died from endocarditis.

Acute Disease↗
PubMed1977

Effects of adrenergic stimulation on the choledochoduodenal sphincter mechanism.

The object of this study was to access the effects of systemic bolus injections of epinephrine and of norepinephrine upon the sphincter at the choledochoduodenal junction in the cat and the dog. The bile duct was transected and the downstream segment was cannulated. Two methods were used to assess sphincteric activity. In method I the bile duct was perfused with Ringer's solution at a constant pressure and the flow rate of the solution was recorded. In method II the bile duct was perfused at a constant rate of flow and the terminal intraductal pressure was recorded. Intraduodenal pressure and respiratory movements were also recorded. There was a significant decrease in sphincteric activity following both epinephrine and norepinephrine administration in both cats and dogs, using both constant pressure and constant flow methods.

Ampulla of Vater↗