Biomedical subjects

J H Meyer

Publications and source records attributed to J H Meyer.

At least 19 recordsLinked to original sources

PubMed1992

Findings and implications from research on student learning.

This paper sets out a number of important conclusions drawn from research on student learning in higher education. Although there is an emphasis on medical education, most of the research conclusions presented are relevant to undergraduate education in general. The conclusions and accompanying questions are intended to promote debate among academic practitioners and students on how to improve the quality of student learning. In conjunction with the complementary research review by Entwistle on how departments may influence the quality of student learning, the conclusions and questions presented here formed the basis of a workshop presented at the 1991 Conference of the South African Association for Medical Education held at the University of Cape Town.

Cognition↗

PubMed1992

Sustained slowing effect of lentils on gastric emptying of solids in humans and dogs.

The distal small intestine is an especially potent site for carbohydrate-triggered intestinal inhibition of gastric emptying of solids. Poorly digestible carbohydrates, such as lentils, may escape proximal absorption, travel over time to reach these inhibitory mechanisms, and slow the gastric emptying of a later meal. A slowing effect on gastric emptying may be associated with a lowering effect on postprandial glucose. The aims of this study were to determine (a) whether lentils (a poorly digestible carbohydrate) vs. bread (an easily digestible carbohydrate) eaten as a premeal (with equal amounts of carbohydrates) slow the gastric emptying of a second solid meal taken 4.0-4.5 hours later and (b) whether a slowing effect on the gastric emptying of the second meal is associated with a lower postprandial glucose response. We found that in 7 dogs and 10 humans, gastric emptying of the second meal was delayed after a lentil premeal compared with a bread premeal. However, there was no difference in the glucose response to the second meal under the two conditions.

Adult↗

PubMed1992

Gastric emptying of solid food is most potently inhibited by carbohydrate in the canine distal ileum.

Although glucose sensors regulating the gastric emptying of liquid meals are uniformly distributed throughout the canine small intestine, some data suggest that the distal small bowel more potently inhibits gastric emptying of solid foods. The aims of this study were to compare (a) the inhibition of gastric emptying by glucose sensors in the proximal intestine with the feedback from the distal intestine, (b) these effects on the gastric emptying of solids vs. liquids, and (c) the inhibitory effect of unhydrolyzed starch with glucose. In 7 dogs with chronic duodenal fistulas, the second, third, and fourth quarters of small bowel were perfused via chronically implanted transmural catheters. Gastric emptying of either solids or liquids was tracked by gamma camera while gastric output was diverted out the duodenal fistula and the small bowel perfused with test solutions of glucose (0.06-2.0 mol/L), 0.15 mol/L NaCl, or 8.5% soluble starch. It was found that (a) gastric emptying of solids but not liquids was approximately 3 times more potently inhibited by glucose in the fourth quarter vs. the first or second quarter of small bowel, and (b) only hydrolyzed starch inhibited gastric emptying of solids.

Analysis of Variance↗

PubMed1991

Study approaches of nursing students: effects of an extended clinical context.

In the first part of this study a comparison is made between the approaches to studying adopted by failing and achieving nursing college students. It is concluded that failing students manifest approaches to studying that are, in some respects, conceptually difficult to interpret. This conclusion is presented against a background of similar findings that have emanated from other recent studies on student learning. The second part of this study investigates the influence of contextual perceptions on the manifestation of the approaches to studying adopted by achieving students. In thus exploring the manifestation of different forms of contextualized approaches to studying (which are referred to as study orchestrations) a distinction is made between the influences attributable to 'conventional' and 'clinical' sets of contextual variables. In an extension of previously reported studies, it is concluded that the combined set of these contextual variables explains significantly more of the variation in study approaches than the set of 'conventional' variables. It is further concluded that, under the influence of an extended set of contextual variables, conceptually related, but differing forms, of study orchestration may be manifested; a general form which is readily interpretable in terms associated with 'conventional' academic contextual variables and a clinical form which, in the present study, is associated specifically with a nursing academic environment. The implications of these conclusions for nursing education are discussed and areas for future research are indicated.

Concept Formation↗

PubMed1991

Effects of Furegrelate (Upjohn 63557A) on patency and platelet deposition after canine carotid endarterectomy.

Platelet deposition upon endarterectomy sites is a likely cause for early postoperative thrombosis, embolism and restenosis. Platelets aggregate by the thromboxane-prostacycline mechanism. Thromboxane synthetase inhibitors which have been safely administered to humans should reduce platelet deposition after surgical therapy and therefore reduce peri-operative mortality and the prevalence of stroke. A randomized prospective controlled trial was designed to determine vessel patency and platelet deposition associated with the use of 3 mg/kg and 30 mg/kg of Furegrelate (Upjohn U63557A) daily in dogs, who were to have carotid endarterectomy. The 46 treated and 46 control dogs had total carotid patency of 96% and 76% respectively (P less than 0.01). Fourteen dogs treated with 30 mg/kg Furegrelate had no occlusions, compared with a 19% prevalence in 13 controls (P less than 0.02). Furegrelate 10 mg/kg significantly lowered platelet aggregation. Platelet deposition was not significantly changed, however. The reason for this disparity was a probable persistence of vessel wall factors which promoted platelet deposition. This approach might therefore lower rates of peri-operative thrombosis but it would be very unlikely to alter the incidence of restenosis or embolism. Further research could be directed towards modifying the stimuli for platelet deposition upon the endarterectomy site.

Animals↗

PubMed1991

Effect of hydroxypropylmethylcellulose on gastrointestinal transit and luminal viscosity in dogs.

The effects of hydroxypropylmethylcellulose on upper gastrointestinal transit, viscosity, and water flux were studied in six dogs fistulated at the proximal duodenum and/or mid-jejunum. Combinations of different grades of hydroxypropylmethylcellulose were prepared as 2% or 3.3% solutions to yield input viscosities of low (approximately 5000 cp at 37 degrees C and 1 s-1), medium (15,000 cp), or high (30,000 cp) viscosity. Hydroxypropylmethylcellulose modified intralumenal viscosity, with a linear relationship existing between input and lumenal viscosity. With regard to transit, the lag time before the onset of chyme recovery increased linearly as a function of luminal viscosity. There was also a pronounced decrease in the first-order emptying rate constant as lumenal viscosity increased from water to low-viscosity hydroxypropylmethylcellulose, but as viscosity was further increased there was little additional change. These results indicate that water-soluble fibers can exert a significant influence on both the lumenal viscosity and the transit profile in the upper gastrointestinal tract.

Animals↗

PubMed1990

Gastric emptying of nondigestible solids in dogs: a hydrodynamic correlation.

The influence of particle size, particle density, fluid viscosity, and fluid flow rate on the gastric emptying of nondigestible solids was investigated in five dogs with chronically placed fistulas. Six hundred and fifty particles of 13 different size and density combinations were administered simultaneously with 500 ml of either normal saline or low-, medium-, or high-viscosity polymer solutions. The canine stomach was found to discriminate between these solids on the basis of size and density at all levels of viscosity above saline. The observed patterns of emptying are consistent with the hypothesis that gastric emptying of nondigestible solids is governed in part by hydrodynamics and correlate well with the gastric-emptying coefficient (GEC), a dimensionless grouping of variables that takes the form GEC = (Dpy/Dp) [g(rho f - rho p)Dp2]/[eta (nu)] where [g(rho f - rho p)] is particle buoyancy consisting of fluid (rho f) and particle (rho p) densities and g, the gravitational constant; (Dp) is the particle diameter, (Dpy) the estimated pyloric diameter, eta the fluid viscosity, and (nu) the average linear velocity of fluid exiting the stomach.

Animals↗

PubMed1990

Inhibition of gastric emptying by acids depends on pH, titratable acidity, and length of intestine exposed to acid.

Exposure of the small intestine to acid inhibits gastric emptying in a dose-related fashion that depends on titratable acidity and pH. Little information is available on the location of this inhibitory mechanism or on the relative contribution of titratable acidity and pH to this feedback control. We hypothesized that the dependence on titratable acidity is related to the length of the intestine exposed to acid and that the dependence on pH is related to the region of the intestine exposed to acid. To test these ideas, we studied 11 dogs with duodenal and jejunal fistulas. The inhibitory effects were tested when different lengths of the small intestine were exposed to test solutions of 0.03, 0.06, and 0.12 meq/ml titratable acidities. pH as an independent covariable was separated from titratable acidity by comparing the inhibition of gastric emptying of lactic acid (pH fixed to 2.4) to HCl (pH 0.96-1.6). Maximal inhibition of gastric emptying by both acids depended on acid exposure of a length of small intestine that was greater than 65 but less than or equal to 150 cm long. When acid was confined to the proximal 15 cm, increasing concentration of HCl (decreasing pH) resulted in increasing inhibition, but this effect was absent with increasing concentration of lactic acid (fixed pH). Inhibition was absent when 0.06 meq/ml HCl was infused into the intestine beyond the midintestine.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1990

Inhibition of gastric emptying by sodium oleate depends on length of intestine exposed to nutrient.

Previously, we reported that inhibition of gastric emptying by glucose or acids depends on the length of gut exposed to the inhibitor [Gastroenterology 95: A877, 1988; Am. J. Physiol. 256 (Gastrointest. Liver Physiol. 19): G404-G411, 1989]. In this study, we hypothesized that feedback control by fat may be similarly regulated. In dogs with chronic intestinal fistulas, we compared the intensity of intestinal feedback when different lengths of the small intestine were exposed to meals of 3, 9, or 27 mM sodium oleate. We found that 1) inhibition of liquid emptying was dose dependent, 2) intensity of negative feedback was dependent on both the concentration of the oleate and the length of gut exposed to fat, 3) full inhibitory effect was achieved with exposure of fat to 150 cm of gut, 4) inhibition from the distal one-half of gut was less potent than that generated from the proximal one-half of gut, and 5) on a molar basis oleate was 20 times as effective as glucose at inhibition of gastric emptying and that this difference was related to the slower rate of fat absorption.

Animals↗

PubMed1990

Influence of alumni careers and students' educational pathways on animal science undergraduate teaching programs.

In an attempt to aid the planning of courses and curricula in animal science, a survey instrument concerning careers, opinions and suggestions regarding education received was sent to 1,398 alumni who had graduated during the years 1956 to 1987. Longitudinal studies of 1972-82 entering animal science students, and a telephone survey of students who entered as freshmen in 1985-86, provided information concerning student profiles and educational interests. Fifty-two percent of alumni were women, 61% had obtained advanced degrees, about 50% were veterinarians, laboratory or medical scientists, business owners or managers, only 8% were ranch owners or managers, and the rest were engaged in a multiplicity of careers. Undergraduate experiences judged most important by alumni were obtaining academic skills, followed by advanced biology courses, animal science courses, work experience and developing the ability to continue learning. Alumni suggestions for change gave priority to offering more practical subject matter and business and economics in the animal science program, followed by more general education, research, science and theory, or no change. Approximately 30% of entering freshmen students graduated in the animal science major. Fifteen percent expressed interest in livestock, 23% in horses, 29% in companion animals, and the rest in a wide variety of animals.

Animal Husbandry↗

PubMed1989

Estradiol induces rapid remodelling of plasma membranes in developing rat cerebrocortical neurons in culture.

Exo-endocytotic images and intramembrane particles were quantitatively assessed in freeze-fracture replicas from the plasma membrane of dispersed fetal rat cortical neurons (day 16 gestation) grown for 24 days in culture. The addition of 10(-10) M 17 beta-estradiol to the culture medium resulted in a significant increase in the numerical density of exo-endocytotic images within 1 min. A further increase of the number of exo-endocytotic images associated to a significant decrease in the number of intramembrane particles was observed in cells exposed for 10 min to 17 beta-estradiol. Similar results were observed when the cells were exposed to 17 beta-estradiol for 17 days. No effects on exo-endocytotic images and intramembrane particles were observed when 17 alpha-estradiol was added, instead of 17 beta-estradiol, to the cultures. These results indicate that physiological levels of 17 beta-estradiol can have rapid effects upon the ultrastructure of the neuronal membrane of developing cerebrocortical neurons.

Animals↗

PubMed1989

Intraluminal calcium binding does not mediate fatty acid-induced pancreatic bicarbonate secretion.

Since the chain length dependency of fatty acid-induced pancreatic exocrine secretion parallels that of fatty acid-induced inhibition of gastric emptying, similar mechanisms of action may be involved. An earlier study suggested that binding of calcium might mediate fatty acid-induced inhibition of gastric emptying. This study investigated possible mediation of fatty acid-induced pancreatic secretion by calcium binding. Pancreatic secretory response to intraduodenal administration of dodecanoate and various calcium chelators (sodium EDTA, calcium-saturated EDTA, sodium dodecyl sulfate, sodium dioctyl sulfosuccinate, and sodium taurocholate) was studied in three dogs equipped with chronic pancreatic fistulae. Calcium affinity of the various test solutions was quantitated by titrating aliquots of perfusate against a standard CaCl2 solution. Sodium EDTA was found to be the most potent calcium binder (pKc 8.3); sodium dodecanoate, sodium dodecyl sulfate, and sodium dioctyl sulfosuccinate were moderate calcium binders (pKc 7.3, 7.2, 6.9, respectively), whereas sodium taurocholate and calcium-saturated EDTA were poor calcium binders. Sodium dodecanoate evoked brisk bicarbonate output (0.6-1.6 mEq/15 min). Minimal secretory responses were observed in response to all other agents tested. These findings suggest that calcium binding is not involved in mediation of fatty acid-induced pancreatic bicarbonate secretion.

Animals↗

PubMed1989

Pancreatobiliary responses to an intragastric amino acid meal: comparison to albumin, dextrose, and a maximal cholecystokinin stimulus.

Little is known about how gastric and pancreatobiliary responses differ after intake of elemental diets from responses to polymeric food. We therefore compared pancreatic and biliary secretions after gastric instillation of albumin (7 g%, with dextrose 21 g%) with an elemental diet in 6 healthy volunteers. The elemental diet contained amino acids (7 g%, with dextrose 21 g%) in the same molar composition as the albumin. Furthermore, we studied the effect of a pure intragastric dextrose solution (21 g%) on pancreatobiliary secretions, as glucose constitutes a major component of elemental diet formulas. The various pancreatobiliary responses were tested against a maximal i.v. cholecystokinin stimulus. The dextrose, amino acid, and albumin meals emptied at similar rates, and gastric emptying was completed within 3 h. Similar pancreatobiliary responses were observed after the albumin and amino acid meals, but response to both the amino acid and albumin meals was smaller than to the intravenous cholecystokinin stimulus. The glucose meal caused a marked and sustained stimulation of pancreatobiliary outputs, which did not differ significantly from the other test meals. However, lower cholecystokinin levels were observed after the glucose meal compared with distinct cholecystokinin release after the albumin and amino acid meals. We conclude first that there are no major differences in secretory responses between elemental (amino acid) and polymeric (protein) meals and second, that intragastric pure glucose meals strongly stimulate pancreatobiliary secretions. The marked pancreatic and biliary responses to intragastric dextrose cannot be fully explained on the basis of cholecystokinin release, suggesting that this response is probably mediated by neural mechanisms.

Adult↗

PubMed1989

GIP and insulin release in relation to gastric emptying of a mixed meal in man.

To clarify the role of GIP (gastric inhibitory polypeptide) as an incretin, we related temporally the gastric emptying of fat, protein and glucose to plasma levels of glucose, GIP and insulin in man. Five healthy volunteers with a multiple lumen duodenal tube ingested a mixed meal with phase-specific markers for the aqueous phase, liquid fat and the solid protein phase. Duodenal passage was determined by intraduodenal infusion of a second set of phase-specific non-absorbable markers. Plasma insulin rose rapidly from a basal value of 59 pM to 300 pM at 60 min, and then declined to reach basal levels after 180 min. By contrast, plasma GIP rose more slowly than insulin, from a basal value of 9.4 pM, and remained elevated, in the range of 14-18 pM, throughout the 240 min observation period. The time course of plasma insulin concentration paralleled gastric emptying of the aqueous phase, containing most of the meal's glucose (r = 0.952, P less than 0.001). The time course of plasma GIP concentrations paralleled the gastric emptying of fat and protein (r = 0.763-0.834; P less than 0.01-0.05). Plasma insulin concentrations showed no correlation to the rate of emptying of fat and protein (r = 0.142-0.420; n.s.) and to plasma levels of GIP (r = 0.365; n.s.). The threshold for plasma glucose at which GIP would exert an incretin effect only reached at one time point, 30 min after ingestion of the meal. Our findings of simultaneously tracked gastric emptying of meal nutrients, hormone release and plasma glucose levels do not support an important physiological role for GIP as an insulinotropic hormone after ingestion of mixed meals in man.

Adult↗

PubMed1989

Influence of the organophosphorus compound DFP on inhibitory motor systems and esterase activity in the spinal cord of cats.

In high spinal cats, the acute time-dependent changes of both the activity of spinal reflex pathways and the activity of three different esterases (acetylcholinesterase, carboxylesterase and neurotoxicant target enzyme) in the spinal cord were investigated after intravenous application of the organophosphorus compound di-isopropyl phosphofluoridate (DFP). There is no general depression of spinal reflexes by DFP. While the recurrent inhibition is completely abolished for a long time and the reflexes to a flexor (PBSt) are depressed but with a shorter recovery time, the reflexes to an extensor (GS) are distinctly less depressed or even facilitated. Reflex pathways from skin afferents to motoneurones did not react in a uniform way to DFP, e.g. inhibitory nociceptive pathways were less affected than excitatory ones. Esterase activities were heavily depressed and recovered with different time courses. The acute DFP action cannot be explained by a uniform intoxication of all spinal functions but probably emerges from a differential action on different interneuronal systems.

Acetylcholinesterase↗

PubMed1989

Alterations in digestive function caused by pancreatic disease.

Pancreatic exocrine secretion is regulated by a complex interaction of meal-stimulated neurohormonal reflexes. Pancreatic enzyme output must be reduced to less than 10 per cent of normal before fat absorption is appreciably impaired, proving that the pancreas secretes a large surplus of enzymes. Surgical therapy does not improve pancreatic exocrine insufficiency, and partial pancreatic resection frequently precipitates steatorrhea in patients with chronic pancreatitis. Therefore, pancreatic resection should be undertaken cautiously in patients who do not yet have clinically evident exocrine insufficiency. In most patients, oral pancreatic enzymes will control diarrhea secondary to steatorrhea. In others, concurrent administration of an H2 blocker is required to reduce gastric acidity and prevent enzyme inactivation in the stomach. Formulations with an acid-resistant coating are also effective in some patients. However, complete normalization of fat absorption with restoration of body weight and nutritional well-being requires careful management of multiple dietary and behavioral factors, as well as long-term follow-up. Unfortunately, this appears to be an elusive goal, as many patients with chronic pancreatitis continue to die of malnutrition.

Digestion↗

PubMed1989

Transient dyserythropoiesis occurring during the involutionary phase of stage IV-S neuroblastoma.

An acutely ill 6-month-old female infant presented with massive hepatomegaly, accompanied by severe anemia with peripheral normoblastemia and thrombocytopenia. Bone marrow examination revealed erythroid hyperplasia with gross erythroid dysplasia, reduced granulocytic precursors, and virtually absent megakaryocytes. The bone marrow also contained completely necrotic cells occurring in clumps as well as singly. The appearances suggested bone marrow involvement by neuroblastoma. Accordingly, combination chemotherapy was instituted and laparotomy was performed as soon as her clinical condition had improved. Left adrenalectomy was carried out, because a small adrenal nodule of ganglioneuroma was present. Liver biopsy showed expansion of portal tracts by loose fibrous connective tissue containing hemosiderin deposits and some degenerate cellular debris, consistent with areas of involuted metastatic neuroblastoma. Complete recovery followed, and subsequent bone marrow examination was entirely normal. It is thought that the dyserythropoiesis probably resulted from the release of toxic metabolites from regressing neuroblastoma.

Adrenal Gland Neoplasms↗

PubMed1989

Inhibition of gastric emptying by glucose depends on length of intestine exposed to nutrient.

Nutrients inhibit gastric emptying in a dose-related fashion. We postulated that load-dependent gastric emptying results from the saturation of mucosal absorptive mechanisms, so that a longer length of the small intestine is exposed to unabsorbed nutrients as more nutrient enters the intestine to participate in this negative feedback. To test this idea, we limited exposure of 0.25 to 1.0 M glucose meals to various lengths of duodenum and jejunum in 17 dogs. The effects of these limited perfusions were then compared with experiments in which the whole gut (ALL) was exposed to the nutrient. Maximal inhibition was seen with 1.0 M meal and was similar with perfusions of 150 cm and ALL. By contrast, even with the 1.0 M load, no inhibition of gastric emptying was seen when glucose meal was confined to the first 15 cm of the proximal duodenum. Only 50-60% of maximal inhibition was observed during confinement of 1.0 M meal to the proximal 65 cm. We concluded that glucose sensors are present in both the proximal and the distal gut and the inhibition was related to the length of the small intestine exposed to glucose.

Animals↗